Saturday, August 31, 2013

North Atlantic Oscillation 2013-2014 Winter Forecast

This is the forecast for the North Atlantic Oscillation in the winter of 2013-2014 by The Weather Centre.

The North Atlantic Oscillation is an index known by a few, but unknowingly adored by snow lovers along the Eastern Seaboard. It can also be the source of fantasies for those in the Midwest. Regardless of where you live, chances are, when the term 'Nor'easter' comes up, it's due to the North Atlantic Oscillation.


The North Atlantic Oscillation (henceforth may be referred to as the NAO) is an atmospheric index that is determined by the pressure differences between a body of high pressure in the Atlantic and a body of low pressure over Greenland. The NAO has two phases- positive and negative. In the positive NAO, these two areas of different pressure are maximized, with the high pressure getting higher and the low pressure getting lower. The positive NAO results in warmer than normal temperatures for some in the Eastern US, and an unfavorable snow environment for many east of the Mississippi River. In the negative NAO, the low pressure over Greenland is weakened, sometimes to the point of where high pressure takes over that area. In similar fashion, low pressure over the Atlantic weakens, and the results for those in the United States are remarkable. The negative NAO sets up a pattern conducive for the formation of the 'Nor'easter' system that brings significant snow (and sometimes rain) to many in the Northeast US. The negative NAO can also bring snowstorms to the Midwest and Ohio Valley, but the negative phase is most renowned for its Nor'easter formation potential.

Now, I gathered two analog years in my Preliminary winter forecast I issued in June. I indicated my prime analog was the winter of 1962-1963. Since the release of that forecast, new data has strengthened the argument for 1962-1963 as being my top analog. Because this analog has been strengthened by new evidence, it remains my primary analog.

Shown above is a map of the mid level atmospheric flow in the winter of 1962-1963. Yellows and reds indicate high pressure, while blues and purples depict low pressure. We want to look towards Greenland at this point. When we find that land mass, we see an abnormally large area of high pressure in and just to the east of Greenland. If you recall in my explanation of the NAO, high pressure over Greenland indicates the formation of the negative NAO. Consequently, low pressure anomalies have developed over much of the Eastern and Central US. It is likely that, should my primary analog verify, the NAO would remain negative for the majority of the winter.

Despite the favorable analog positions, rather iffy sea surface temperatures and long range model forecasts tell me it will most likely not be extremely negative- a moderately negative NAO is more probable.

Here is my forecast for the North Atlantic Oscillation.

Andrew

Arctic Oscillation 2013-2014 Winter Forecast

This is the winter forecast for the Arctic Oscillation in 2013-2014 by The Weather Centre.

The Arctic Oscillation drives much of the winter, especially in the temperature department. It is one of a couple smaller-scale factors that wield major influence on the nation's weather come winter. Using data gathered over the past few months, I was able to make a forecast.

The Arctic Oscillation (henceforth referred to as the AO when mentioned) involves the strength of the jet stream encompassing much of the Arctic Circle. The AO has two phases: positive and negative. In the positive phase, the jet stream over the Arctic strengthens. In response, the cold weather is literally locked up and cannot escape the strong jet stream. Consequently, portions of Europe and many in North America observe above normal temperatures. In the negative phase of the Arctic Oscillation, the polar jet stream is abnormally weak as high pressure enters the Arctic. This allows the cold air to shift out of the Arctic and down to lower latitudes. Depending on other atmospheric factors in play at that point in time, the cold air can reach the United States, Europe, or Asia. All three could be affected, but again, other atmospheric factors will limit and enhance the extent of this cold air.

Now, I gathered two analog years in my Preliminary winter forecast I issued in June. I indicated my prime analog was the winter of 1962-1963. Since the release of that forecast, new data has strengthened the argument for 1962-1963 as being my top analog. Because this analog has been strengthened by new evidence, it remains my primary analog.

Shown above is a map of the mid level atmospheric flow in the winter of 1962-1963. Yellows and reds indicate high pressure, while blues and purples depict low pressure. We want to look to the middle of the map to find the Arctic Circle. When we see it, we come upon two large areas of high pressure that are splitting up the Arctic Circle. This is a key notice that we are observing the negative phase of the Arctic Oscillation. The two high pressure areas are not allowing the polar jet stream to strengthen, and as a result, low pressure anomalies form at lower latitudes in North America and Europe, bringing with them below normal temperatures. Considering this is currently my prime analog year, along with a couple other points that cannot be expressed right now due to the possibility of confusion, I find it very plausible we see the Arctic Oscillation average out to negative once the three winter months of 2013-2014 have come and gone.

All that said, here is my forecast.


Andrew

2013-2014 City-by-City Winter Forecasts: Idaho Falls, Redding, Green Bay, Rochester

Idaho Falls, Idaho

Temperature: Average
Precipitation: Slightly Above Average
Snowfall: Slightly Above Average
Confidence: Slightly Below Average

Redding, California

Temperature: Slightly Above Average
Precipitation: Slightly Below Average
Snowfall: Slightly Below Average
Confidence: Below Average

Green Bay, Wisconsin

Temperature: Below Average
Precipitation: Slightly Above Average
Snowfall: Slightly Above Average
Confidence: Above Average

Rochester, New York

Temperature: Below Average
Precipitation: Above Average
Snowfall: Very Above Average
Confidence: Slightly Above Average

2013-2014 City-by-City Winter Forecasts: Omaha, Pierre, Tucson, Los Angeles

Omaha, Nebraska

Temperature: Slightly Below Normal
Precipitation: Slightly Below Normal
Snowfall: Slightly Below Normal
Confidence: Below Normal

Pierre, South Dakota

Temperature: Above Normal
Precipitation: Below Normal
Snowfall: Slightly Below Normal
Confidence: Above Normal

Tucson, Arizona

Temperature: Above Normal
Precipitation: Below Normal
Snowfall: N/A
Confidence: Below Normal

Los Angeles, California

Temperature: Above Normal
Precipitation: Normal
Snowfall: N/A
Confidence: Very Below Normal

2013-2014 City-by-City Winter Forecasts: Jacksonville, Columbus, Lansing, Fort Smith

Jacksonville, Florida

Temperature: Average
Precipitation: Slightly Above Average
Snowfall: N/A
Confidence: Average

Columbus, Ohio

Temperature: Below Average
Precipitation: Average
Snowfall: Average
Confidence: Slightly Below Average

Lansing, Michigan

Temperature: Below Average
Precipitation: Average
Snowfall: Above Average
Confidence: Slightly Above Average

Fort Smith, Arkansas

Temperature: Average
Precipitation: Average
Snowfall: Average
Confidence: Below Average

2013-2014 City-by-City Winter Forecasts: New York City, Boston, Annapolis, Charlotte

New York City, New York

Temperature: Below Normal
Precipitation: Above Normal
Snowfall: Above Normal
Confidence: Above Normal

Boston, Massachusetts

Temperature: Below Normal
Precipitation: Above Normal
Snowfall: Above Normal
Confidence: Above Normal

Annapolis, Maryland

Temperature: Below Normal
Precipitation: Above Normal
Snowfall: Above Normal
Confidence: Normal

Charlotte, North Carolina

Temperature: Slightly Below Normal
Precipitation: Above Normal
Snowfall: Slightly Above Normal
Confidence: Slightly Below Normal

2013-2014 City-by-City Winter Forecasts: Chicago, Nashville, Denver, Houston

Chicago, Illinois

Temperature: Below Normal
Precipitation: Average
Snowfall: Average / Slightly Above Average
Confidence: Average

Nashville, Tennessee

Temperature: Below Normal
Precipitation: Above Average
Snowfall: Slightly Above Average
Confidence: Above Average

Denver, Colorado

Temperature: Average
Precipitation: Slightly Below Average
Snowfall: Slightly Below Average
Confidence: Below Average

Houston, Texas

Temperature: Above Average
Precipitation: Slightly Above Average
Snowfall: N/A
Confidence: Average

Official 2013-2014 Winter Forecast

 See the other winter forecasts for cities across the country, the AO, NAO and even Canada and Europe! Click Here

"Much of the nation can expect some frigid weather this winter."

Hello everyone, and welcome to The Weather Centre's Official 2013-2014 Winter Forecast. This forecast will examine the indices most likely to play a significant role in the coming winter, as well as several hints and clues we can pick up from the weather we experienced this past summer. Bear with me- this post is quite long, but I promise you it will still be easy to understand no matter how into weather you may be.

We will begin with an analysis of one of the main drivers of the seasonal climate, the El Nino-Southern Oscillation (ENSO).

This chart shows sea surface temperatures for the four regions included in the El Nino-Southern Oscillation (ENSO) phenomenon. The ENSO phenomenon involves anomalous sea surface temperatures across these four regions on the chart above. When sea surface temperatures are below normal in the second graph from the bottom, it is said that a La Nina is in place. In similar fashion, above normal sea surface temperatures (SST's) in the Nino 3.4 region correspond to the term 'El Nino'. Both the La Nina and El Nino have different effects on the United States- an El Nino brings about a snowy and cold East Coast, while allowing warm and dry weather to flourish in the Plains and Midwest. A La Nina permits cool and snowy weather to hit the Ohio Valley and Midwest, while warming up portions of the Southern US. Looking at the image above, I want to focus on the bottom chart first, labeled Nino 1+2. The Nino 1+2 area is located in the waters just offshore of Ecuador, as the image below shows:

The Nino 1+2 region has been rather significantly below normal for the past summer, at one point reaching the -2.0 level (which is very negative). The Nino 3 and 3.4 regions also were below normal for the summer, but it is apparent that the Nino 1+2 and Nino 3 regions held the brunt of the cold. Statistics from Americanwx user donsutherland1 indicate that when the Nino 1+2 region is below normal in summer, 83% of cases led to La Nina development in the winter. The other 17% of cases led to Neutral ENSO development, which means SST's are not cold enough to be a La Nina, and are not warm enough to be called an El Nino. The water temperatures are neutral.

This animation shows temperature composites for west and east-based La Ninas and El Nino's. The difference between west and east based is in the name: If you have something that's west-based, it means the temperature anomalies of an El Nino or La Nina are on the western side of the ENSO monitoring area. Likewise, an east-based El Nino or La Nina means anomalous sea surface temperature anomalies are in the eastern side of the ENSO monitoring area. Currently, if one was to classify the ENSO situation, we would be in an east-based La Nina, which would support a cooler than normal Northern US. Don't get too hung up on this item, though; the east-based region (Nino 1+2) is notorious for not affecting the weather in North America too much.


Model guidance from the ECMWF model ensemble system suggests the current ENSO state will warm up to a weak El Nino by the time winter rolls around. Due to the aforementioned statistics on a cold Nino 1+2 summer and winter consequences, as well as forecasts in the past that indicated we were supposed to be well into an El Nino by now, I'm pretty skeptical on the idea of an El Nino. Right now, I believe we will see a Neutral ENSO winter, though if water temperatures stay cold enough we could see a weak La Nina.

We now take a broader look at the sea surface temperatures around the globe to get a feel for other atmospheric patterns that rely on these sea surface temperature anomalies (SSTA's) to work. The first one we will look at is the Pacific Decadal Oscillation, or PDO.

The PDO has two phases- a positive (warm) phase, and a negative (cool) phase. In the +PDO phase, we see below normal sea surface temperatures extending from northeast Asia across the North Pacific and to the waters well offshore Western Canada and southern Alaska. Immediately offshore of these regions, we see above normal SSTA values. The opposite set-up occurs in a -PDO. In the negative PDO, we find above normal SST anomalies stretching from east Asia across much of the northern Pacific and into the Northeast Pacific. Below normal SST values are found just offshore the western coast of North America.

In the positive PDO, the Southeast tends to experience above normal precipitation, while the southern Ohio Valley will see slightly drier than normal conditions. In the temperature department, just about everyone east of the Front Range experiences below normal temperatures, except the Northern Plains, which sees above normal temperatures. The negative PDO sees the opposite of all this, with much of the US warm in a -PDO, and precipitation trends finding the Southeast in a dry area, but the lake effect snow belts in the Great Lakes at above normal precip levels. Right now, the PDO appears to be trying to switch phases from negative to positive. At the moment, I'm still expecting a negative PDO for the winter, and the chances of a neutral to slightly positive PDO this winter are low, but not completely zero.

Looking back at the global SSTA chart above, we see rather variable sea surface temperatures in the waters in northeast Canada and by Greenland. This means the positive Atlantic Multidecadal Oscillation (AMO) we have been seeing recently is losing its grip. A +AMO is defined by above normal sea surface temperatures in the Arctic Ocean, and a negative AMO sees the Arctic Ocean in cooler than normal temperatures. A +AMO tends to enhance the likelihood of a negative North Atlantic Oscillation, which then helps cold and snow enter the Northeast and overall Eastern US. If we see that the +AMO is weakening (which it has been over this past spring), it does not bode well for the chances of a negative NAO this winter. Luckily, the AMO is just one of many factors that go into the chance of a negative NAO, many of which we will discuss below. For this winter, I anticipate the AMO to be rather neutral, maybe a bit negative.

To round out this SST discussion, research I have conducted does indicate that there is a solid connection between sea surface temperatures and high/low pressure anomalies. For example, positive SSTA's lead to higher pressure, while negative SSTA's lead to lower pressure. Because sea surface temperatures take a prolonged period of time to cross the anomaly spectrum (from below normal to above normal or vice versa), we can begin looking at global SST's to find potential locations for mid level height anomalies. Right off the bat we see strong positive SST anomalies across the Pacific. This bodes well for high pressure placement in the Bering Sea and general North Pacific, something I will discuss further in my analog package discussion below. A concerning item is the above normal SST swath off the East Coast. If this body of +SST anomalies leads to high pressure formation, it could happen that we see periods of anomalously warm weather along the Eastern Seaboard that could then maximize cold weather in the Plains. But that's still a while away.

Here's the basis of why I'm issuing my winter forecast so early: my winter analog package. I took into account many factors, including the PDO, ENSO, AMO, and sunspot numbers, with many others also adding to the mix.

The years I took into account were 1962-1963 and 2008-2009. I did drop my previous analog year of 1951-1952 due to an uneasiness I had using it. These years were chosen after an initial check back in the spring for my Preliminary 2013-2014 Winter Forecast, and were recently put through a rigorous examination to assure these are the two years that fit the bill for my analog package.


The first item we will analyze is the mid level atmospheric pattern for the winters of these two analog years. Right off the bat, we note significant below normal height anomalies across North America. This bodes well for below normal temperatures in Canada, extending into the United States. Taking a glance across the Arctic Circle, we find positive height anomalies stretching from Greenland to the Bering Sea. These two positive height anomaly areas do three things that significantly impact winter weather across the Northern Hemisphere:

I: The Polar Vortex is disrupted.
Take a look at the North Pole. We do not see any significantly below normal height anomalies that are composed in one fragment over that region. Rather, we see the two aforementioned positive height anomaly areas disrupting this negative height anomaly area. Thus, the polar vortex, which encompasses a massive amount of cold air from the Arctic, is permitted to weaken and slide to lower latitudes. If the analog package verifies this winter, it is very possible the polar vortex may shift into North America.

II: Sudden Stratospheric Warming (SSW) Chances Increase.
It is well established that the Bering Sea is a favorite place for the origination of sudden stratospheric warmings (SSW's), a phenomenon that involves rapid warming in the stratosphere that then allows unusually cold air to reach the surface and lower latitudes just a couple of weeks later. Last winter, we saw a magnificent SSW originate from the Bering Sea, and other warmings attempt to take place in that same vicinity. With positive height anomalies stationed over the Bering Sea, intrusions of warm air by these positive height anomalies into the Arctic are more easily accomplished, thus increasing the likelihood of SSW events. Due to very strong +SST anomalies across the Northern Pacific and extending into the Bering Sea, chances of persistent high pressure in this area would drastically rise if the current water temperature pattern does not significantly change by the time winter comes.

III: The North Atlantic Oscillation is Negative.
The North Atlantic Oscillation (NAO) is a phenomenon that involves height anomalies across Greenland. In the negative NAO, high pressure is stationed over the land mass in a move that permits cold air and Nor'easter's to affect the Eastern US. On the other hand, a wintertime positive NAO results in a warmer United States with lower probabilities of big snowstorms for the nation as a whole. The analog package above suggests that the upcoming winter NAO will tend to be on the negative side.


Next, we'll take a look at temperature anomalies for these two analog years. It is clear that, should the analog package verify, the trend across the nation would be for below normal temperatures. These below normal temperature anomalies were mainly produced by a very cold winter of 1962-1963, which is the analog year I am favoring out of the two. The Great Lakes was hit hardest by the cold, with the Northern Plains in close second. The West US region manages to emerge from this cold nation to an above normal winter prognosis of these two analog years.



Precipitation anomalies were very dry across the nation as a whole, which I'm pretty skeptical of going into this winter. Indications are that the Southern Plains precipitation trend should verify in response to ongoing drought conditions, but I am not sure about those drier than normal anomalies stretching into the Midwest and Ohio Valley. The same goes for the Mid-Atlantic. I do anticipate either an average or slightly below average Southeast this winter. Expect a general dry trend across the West US if predicted ridging along the West Coast holds up.


Let's take a look at the stratosphere height anomalies for the two winters. It's pretty obvious that the stratosphere was not in good shape for these two winters in the sense that the polar vortex is nowhere near its normal place in the upper latitudes; rather, we find it unusually weakened and stationed in western North America. The positive height anomaly dominance, combined with favorable SSW probabilities due to the Bering Sea height anomalies tells me that the stratosphere will see the polar vortex struggling at points in the upcoming winter.

Let's take a look at why the polar vortex is so depleted here. We have already established that we have a positive QBO in place, which helps to strengthen the polar vortex. It is currently rounding out from its mature phase, which was seen in mid July. The issue here is that both of my analog years had a positive QBO, while a +QBO for this upcoming winter is to be decided by how quickly the current +QBO pulse wants to progress. If we do have a negative QBO come winter, chances are the polar vortex would be stronger than what my analogs are predicting above, but if persistent high pressure sets up in the Bering Sea, I wouldn't be too concerned. It does appear the QBO is now trying to move to a negative phase, which would allow for not as strong a polar vortex this winter. Chances are modest that we will embark upon a negative QBO by the start of winter, but the probability of getting to a -QBO in the second half of winter is much more favorable.


An item I did not previously put into my analog set is the sunspot number we have seen this past summer into fall. The chart above shows the sunspot number since 2000 to the current date. To give a little perspective on how this chart works, take a look at the line between the numbers 11 and 12, which signifies the sunspots in the year 2011. You can see a spike in sunspot numbers immediately prior to the line numbered 12, which tells us the sunspot number spiked in the fall of 2011. It's no coincidence the winter of 2011-2012 came out as a very warm winter as a result of this spiking sunspot number. We saw a spike in sunspot numbers just three or four months into this year, which led to a large heat wave in June into July. Now, as we head into the fall, sunspot numbers have plummeted. Could this lead to a cooler fall? No doubt it will not be warm, and chances are heightened that the fall season will be a bit chilly. If we see plummeting sunspot numbers continuing into the fall, I would be pretty confident in a cold winter ahead. But once again, we would need to see rather consistent low sunspot numbers.

Alright, enough of the explanations. Let's get to the forecast.

We'll start with temperatures. I anticipate a chilly winter for many in the Plains, Great Lakes and East US. Due to the likely presence of a Southeast Ridge at times, I cut off portions of the coast for these cool temperatures. The threat of ridging across the northern Atlantic adds to uncertainty for the Northeast. It is the Midwest and western Great Lakes regions that are likely to get the core of this winter's cold. A favorable analog package, combined with favorable model forecasts make me believe that it will be cities like Chicago, Minnesota, St. Louis and Dubuque that may see the coldest weather of the season. It should be noted that there is potential for this cold to be delayed until the second half of winter, should the fall pattern turn out warmer than expected. I anticipate a warmer than normal Southwest, and this may have to be extended along the West Coast in a later outlook if model forecasts remain consistent with their current outlook.

Precipitation is a wild card this year. With a ridging pattern expected along the western coast of North America, drier than normal conditions are expected. I'm not completely confident in the entire Western US receiving dry weather, which is why it is labeled 'Rather Dry' over just dry. Due to the ongoing drought in the South Plains, dry conditions are likely for that area. Such dry conditions may be maximized in Texas. Above normal precipitation should present itself across the Midwest and central Great Lakes in response to a favorable storm track, and this brings us to the Plains area. I could see this going either way. For one, if we see ridging in the West shift to the east, drier conditions would be more likely. On the other hand, if we see many pieces of energy riding the jet stream through this area, above normal precipitation may fit the bill. The East Coast should average out around normal.

And now for the forecast you have all been waiting for: the snowfall forecast. I anticipate snowy conditions across the Great Lakes, Upper Midwest and the overall Midwest. This is a combination of a favorable (and likely active) storm track across the area, and what could be a rather persistent Southeast Ridge. I would not be surprised to see multiple subsantial snow events for cities like Detroit, Chicago, Cleveland, Indianapolis, and even Green Bay. The below normal snow forecast in the Plains is a bit misleading. It goes along the lines of what I discussed with the Plains precipitation forecast and how it could go either way. So please don't get disappointed if you are in the below normal snowfall area; it is very much subject to change.

Bear in mind this is all subject to change. If you have questions, put them in comments below and I will try to answer them when I find the time. The final winter forecast will most likely come out in late October.

Andrew

Friday, August 30, 2013

Stratospheric Warming Event Taking Place

A stratospheric warming event is taking place as we round out the month of August. You may be wondering how the stratosphere can be experiencing a warming event because we are in summer and not winter. Truth be told, the stratosphere can warm at any time- the reason it warms so significantly in the winter and barely at all in the summer is because of just how dynamic the atmosphere is in the winter with the polar vortex, Arctic Oscillation and all that jazz.

Back to the point, the arrows on the images on the chart above show where this warming event is occurring. At the moment, we see the strongest activity placed between the 40N and 70N latitude areas. This corresponds roughly to the area between the southern Great Lakes and Mid-Atlantic to northern Canada when looking at the North American continent. Because this is a stratospheric warming event, I do anticipate a body of colder air to transition from the upper atmosphere down to the surface, just as what happens in a winter stratospheric warming event.

The question is, where will the cold air end up? Remember that the 40N - 70N area includes the rest of the world, and the effects of stratospheric warmings are not limited to North America. A quick glance at ensemble projections of the mid-level atmospheric height anomalies beyond the 10 day period shows a troughing pattern over the Great Lakes. This could clear the way for not only cooler weather created by the troughing pattern, but also, if the atmosphere cooperates, colder weather being shifted to the surface from this stratospheric warming event. But at of right now, this is all educated speculation.

Andrew

Official 2013-2014 Winter Forecast Comes Out Tomorrow

The Official 2013-2014 Winter Forecast comes out TOMORROW at 12:00 PM Central Time.

Also coming out tomorrow at noon are the 20 pre-selected cities' winter forecasts, and the winter forecasts for the North Atlantic Oscillation and Arctic Oscillation. 

Winter is quickly approaching!

Andrew

Monday, August 26, 2013

2013-2014 Winter Update: August 2013

With just 5 days left until the release of my Official 2013-2014 Winter Forecast PLUS 20 selected cities' winter forecasts at noon central time, I'll shed a little light on where we currently stand in the atmosphere, and what implications it could have for this winter.

Let's start off with sea surface temperatures over the world's oceans. Sea surface temperatures are significant indicators to high and low pressure formation over certain areas, so we want to be paying close attention to these SST charts as we move on through fall and into winter. There are a few areas I want to point out for this SST chart. The first region of interest is the body of above normal sea surface temperatures across the northeast Pacific. Per recent developments around the Pacific, the negative PDO regime that has been holding a grip over synoptic weather in North America for years now, dissipated. In its place, we have strong +SST anomalies. I'm feeling pretty good about the placement of those +SST anomalies, in the sense that such warm temperature anomalies could provoke persistent high pressure formation over the west coast of North America, which would go hand in hand with my analog set for this winter, which also shows high pressure straddling the west coast of North America. This persistent high pressure along the west coast of North America could very well then provoke a positive PNA pattern, which would add to cold weather prospects for the Central and East US. But of course, this is all educated speculation.
Moving on to the temperature anomalies along the Atlantic waters stretching from the Canadian Maritimes directly west to Europe, we see +SST anomalies in this area. Just like the Pacific, these +SST anomalies could provoke high pressure anomalies over the Atlantic, and this is something I have seen in another analog set I published on this blog, and do not discount the idea of such a scenario unfolding. If we look north into Greenland and the bodies of water in Canada, we see a continued trend of positive SST anomalies. If these positive SST anomalies continue into the winter, we could see the chances of a negative NAO increase, which could then lead to increased instances of coastal storms along the Eastern Seaboard. However, these coastal storms could go to the Midwest if that Atlantic ridging pattern I discussed earlier works out and expands into the East Coast. Again, it's all educated speculation.

Next, we will take a look at stratospheric temperature anomalies. The graph above comes from the Japan Meteorological Agency, and shows 30 millibar temperatures (black line) superimposed on the average 30mb temperatures for that time of year (gray line). The trend this summer has been above normal stratospheric temperatures, and the 30mb level is included in this trend. The upper stratosphere is not really included in this above normal temperature trend, but the mid and lower stratospheric levels are, and it is these two regions of the stratosphere that hold the strongest influence on the weather down here in the troposphere. This is all good news for winter weather lovers, especially if the warm stratosphere trend can continue through the fall and into winter.

This image shows zonal-averaged winds at the 30 millibar level- this is the same level we discussed in the temperature chart above. However, this zonal wind graphic has a much different bearing on winter weather. Take a look at the blue line stretching along the far left side of this chart. See those blue colors? That is a trademark sign of a westerly (positive) QBO. The QBO involves the stratospheric zonal wind pattern, and can have strong impacts on winter weather. The positive phase of the QBO means the stratosphere is less inclined to experience sudden stratospheric warming (SSW) events. If you recall from this past January, SSW events can lead to Arctic outbreaks of cold air, if the pattern is right. So, if you like winter weather, you don't want to see a +QBO for the winter. But let's look a little closer at this +QBO. As you can see, the blue strip of positive zonal wind anomalies signifying the positive QBO has been present since roughly May, and has strengthened since mid July. But look at the zonal wind chart since then. If you look closely, you can see the blue strip slowly narrowing along the 10S line on the bottom legend of this chart. Looking even closer along the EQ line right at the end of the left side of the graphic, you can see the darkest blue color is starting to become raggedy, and not as strong as it was earlier in June and July. If you didn't really see what I'm talking about, this is the point: there are small signs that the positive QBO is weakening. This would be great news for trying to break out of the positive QBO pattern and getting into at least a neutral QBO, which would enhance chances for sudden stratospheric warming events that would have otherwise been hampered by the +QBO.

All in all, there's still a lot of time until winter comes around, but current trends are rather favorable for this winter in terms of cold weather for the Plains, Midwest and portions of the East US.

Remember: The Official 2013-2014 Winter Forecast comes out at 12:00 PM Central Time this Saturday, August 31.

Andrew

Sunday, August 25, 2013

Tropical Activity About to Spike; Landfall Threat Low

Tropical activity across the Atlantic basin is about to spike, with the GFS model predicting the development of two tropical cyclones in just over a week's time.

This spike in tropical cyclone development comes as a Madden-Julian Oscillation pulse creates a favorable tropical cyclone development environment for the Atlantic. Those more familiar with the MJO may recognize this as Phase 8 and 1. As the MJO pulse pushes over the Atlantic, it is expected tropical waves shifting west from Africa will have a favorable environment to develop. When they move out to sea, it appears probable that the northern Caribbean may be scraped by the first tropical cyclone, as the GFS forecast above shows. Beyond that, the dome of high pressure stretched across the Atlantic should erode to a point where both cyclones would be able to curve north and east, away from the US Mainland.

Beyond this first spike in activity, ridging in the north Atlantic should rebuild, and any tropical cyclones that develop in the next 14+ days after these two cyclones could move west enough to threaten the Gulf and western Caribbean. Of course, this is all speculation, but we are rapidly approaching peak hurricane season, and these spikes of tropical cyclone development are to be expected as we move through the rest of August, September and even into a bit of October.

Andrew

Saturday, August 24, 2013

Significant Heat Wave Next Week May Become Prolonged

The anticipated heat wave that will begin to push east over much of the nation over the coming workweek will eventually draw back west, but will be able to sustain itself in that position.

The GFS model forecast above projects a very strong dome of high pressure over the Plains, extending its influence across much of the nation and into the Eastern Seaboard. The entrance of lower heights into the West Coast provides reason as to why the ridge of high pressure has decided to pulse east, but as soon as those lower heights shift east, it is likely portions of the East US will see a reprieve from the expected hot temperatures.

This shift of hot weather into the east US coincides with the development of a moderate to strong MJO wave that will be entering Phase 8 or 1 in coming days. Temperature composites on the left-hand side of the graphic show that Phase 1 of the MJO sees warm temperatures across much of the nation, and this will certainly be shown by this ridge of high pressure that will encompass much of the nation to kick off the workweek. Models then diverge, but the European and American ensemble suites seem to be insistent on keeping the MJO wave around Phase 1 territory. This could easily pressure the dome of high pressure into shifting east again at any time after it retreats west towards the end of the upcoming week. Basically, this could be a prolonged warm weather event. This does all depend on if model projections are correct, and we all know that high confidence in medium/long range models is playing with fire. Very long range forecasts from the European weather offices see the MJO shifting towards Phase 2, which would likely alter the weather pattern into one that sees portions of the East and Central US getting a break from the warm weather. But if the MJO stays in Phase 1, millions of people in the United States may be dealing with several days of anomalously hot temperatures.

Andrew

Tuesday, August 20, 2013

New Long Range Models Support Theory of Cool Winter

A new suite of long range models has come in, and continues to support the idea of a cold winter for the Central and Eastern US.

The image above is just one of many long range models showing a favorable atmospheric set up for the winter of 2013-2014. You may remember the following five points from a winter post I made a little while ago. While you may frown upon how this information is not 'new', the reason I do not update it is because the information here is still valid, and that's something winter weather lovers should be happy about.
These are the five things I have seen in new long range forecasts over the past week or so.

1. Active East Asian Jet Stream 
You will see a tightening of the contour lines in eastern Asia on the image above. This symbolizes the jet stream is under stress, thus increasing its strength in that area. From looking solely at the image above, it would appear pressure anomalies are below normal in East Asia, meaning more storms in that region. If you have been with this blog for a while now, you may recall the times I have brought up a correlation between storms in East Asia and storms in the East US 6-10 days later. If the tightening of the jet stream in E. Asia is due to a stormier pattern in that area, it is entirely possible we see a stormier East US.

2. Ridging Pattern in Northern Pacific 
It is well established that the Bering Sea is a favorite place for the origination of sudden stratospheric warmings (SSW's), a phenomenon that involves rapid warming in the stratosphere that then allows unusually cold air to reach the surface and lower latitudes just a couple of weeks later. Last winter, we saw a magnificent SSW originate from the Bering Sea, and other warmings attempt to take place in that same vicinity. With positive height anomalies stationed over the Bering Sea, intrusions of warm air by these positive height anomalies into the Arctic are more easily accomplished, thus increasing the likelihood of SSW events. Once again, this feature has been displayed on multiple forecasts for multiple months now. Additionally, bear in mind that these features were in the forecast when the CFS model was projecting a very cold winter. In my opinion, it could very well be that the CFS is flopping around with its temperature forecast, as is customary of long range models, while the upper level atmospheric flow really tells the story (i.e. the pattern really is favorable for cold weather, even though temperature forecasts do not reflect it). This issue may occur with other models as well, though I have yet to document such an issue in-depth.

3. Ridging Pattern in Western North America 
The image at the top of this post displays a widening of contour lines in western North America. When you get the expansion of these lines, it is typically demonstrative of high pressure anomalies present in the area. The presence of high pressure anomalies in Western Nor. America is defined as a positive Pacific-North American index (PNA) pattern. In response to high pressure in the West US, low pressure (and thus cold air) is favored in the Central and East US. It is also known that a positive PNA results in winter storms taking a track favorable for the Midwest/Ohio Valley to receive snowfall. Yet again, the June CFS forecast identified the +PNA pattern for this winter, just as the current forecast shows.

4. Low Pressure in Eastern North America
 This is kind of an extension of Number 3, in the sense of a low pressure response to positive height anomalies across the West US due to the positive PNA pattern. The new long range models are picking up on those low pressure anomalies, though some are reluctant to allow the anomalies to stretch into the United States. I believe the low pressure anomalies do actually stretch into the US, but because the forecasts are averaged out over time periods of months at a time, the anomalies are not shown correctly.  The reason why the models may be reluctant to do that on the image above is because we could see high pressure in the Bering Sea work against development of the +PNA pattern, thus preventing low pressure anomalies from reaching the US. However, we could also see the Bering Sea positive height anomalies combine with the +PNA in a favorable winter pattern.

5. High-Latitude Blocking Pattern in Greenland
 The image above shows an expansion of contour lines towards Greenland, an indicator that high pressure anomalies are favored in that area. Positive height anomalies in/near Greenland results in the negative phase of the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) is a phenomenon that involves height anomalies across Greenland. In the negative NAO, high pressure is stationed over the land mass in a move that permits cold air and Nor'easter's to affect the Eastern US. On the other hand, a wintertime positive NAO results in a warmer United States with lower probabilities of big snowstorms for the nation as a whole. I brought about the theory that averaging out one to three months in a forecast may not project the real picture, and that theory also applies here. It applies here in the sense that the NAO may be very negative at times, but may also be less negative during some times. The tendency for a more negative NAO over a less negative/more positive NAO for this three month period in winter may then lead to pressure anomalies averaging out positive over Greenland (a sign of the negative NAO), thus showing an expansion of contour lines towards that region.

With many global models continuing to support the five points above, the case continues to build in favor of a cooler than normal winter in the Central and East US. It will be critical to this cold winter theory that we see these five points continue to show up in future model forecasts through September and October. If we can still find these five items in long range forecasts by October, there would be little opposition for these five points to actually verify, and this little opposition for a cooler winter.

Andrew

Saturday, August 17, 2013

Arctic Temperatures Plummeting


Temperatures in the upper Arctic are not only below normal, but are now dropping off a cliff into deep below normal territory.

The chart above shows three lines plotted: the freezing temperature of water (shown by the blue line), the average Arctic temperature in green, and the observed Arctic temperatures in red. It has been well established that the Arctic has been in cooler than normal weather over the summer, but it is only in the last week that temperatures have seriously dropped off.

A temperature analysis chart from August 14 shows a deep pocket of below normal temperatures in northern Greenland, and it appears this pocket is the culprit behind these very cold Arctic temperatures.

Continued below-normal temperatures in the Arctic would more than likely initiate an earlier fall, and possibly an earlier winter in the upper latitudes. Should the atmosphere cooperate, lower latitudes, like the US, could see an earlier fall in the form of colder weather as a product of these extraordinarily cold Arctic temperatures.

Andrew

Friday, August 16, 2013

Invest 92 Eyeing Mexico, Texas for Landfall

As I predicted would happen a few days ago, the tropical system over the Yucatan Peninsula is going to take a westward path and threaten Mexico/Texas in coming days.

The latest suite of model guidance agrees that Texas and Mexico are at risk of this storm making landfall in the next few days, although just how intense the cyclone ends up being is to be determined. Intensity forecasts for this tropical system indicate it has a chance to strengthen to tropical storm status prior to landfall. While warmer sea surface temperatures indicate this could happen, the general trend this year is for tropical systems to not strengthen when they are supposed to. Going with the trend, I anticipate a modest tropical system (meaning some rain, some wind, but NOT a tropical storm or hurricane) to impact either Texas or Mexico.

The HWRF model, a hurricane version of the WRF forecasting model, shows a strong tropical cyclone making landfall in northern Mexico, producing significant rain and wind. It is worth noting that the HWRF is consistently over-exaggerating the strength of any and all tropical cyclones, and thus this forecast is worth little. I put it here to show not only what appears to be the strongest forecast for this invest, but also just to show how weather models are not 100% reliable.

Andrew

Thursday, August 15, 2013

New Developments Strengthen Argument for a Cold Winter Ahead

New and exciting data has been uncovered in recent days that not only has strengthened my analog set for the winter, but has also cut down on a good deal of uncertainty I had up until this point.

This image, put together by Accuweather Forum user Noreaster07, shows a total of five images. The top two images show temperature averages for the winter of 2012-2013 on the left, with the temperature average of the winters of 1982-1983, 1992-1993, and 2001-2002. Both images show a clear warm weather trend over the United States. Moving ahead to the second row of images, March-April temperature composites for this year (left) and the three aforementioned years (right) are shown. Oddly enough, there is another clear similarity between the images. On the bottom image is a composite of winter temperatures for 1983-1984, 1993-1994, and 2002-2003. If the similarity trend continues between these three years and the current year, this would only add to an increasing amount of evidence suggesting we could see a colder winter ahead.

But here's what really excites me: when compared, the winters of the fifth image on the portrait above are similar to my analog set in the mid-latitude atmospheric flow.

This image shows 500 millibar anomalies for the winters of 1951-1952 and 1962-1963 (left), which are my analogs for this winter, and the 500 millibar anomalies for the three winters shown in the last image on the picture at the top of this post. There are a few key things we see here:

1. Active East Asian Jet Stream 
You can see deep negative height anomalies in East Asia on both images in the above composite. This symbolizes the jet stream is under stress, thus increasing its strength in that area. From looking solely at the image above, it would appear pressure anomalies are below normal in East Asia, meaning more storms in that region. If you have been with this blog for a while now, you may recall the times I have brought up a correlation between storms in East Asia and storms in the East US 6-10 days later. If the tightening of the jet stream in E. Asia is due to a stormier pattern in that area, it is entirely possible we see a stormier East US. This stormier East US could also then lead to higher probabilities of Nor'easter's.

2. Ridging Pattern in Northern Pacific 
It is well established that the Bering Sea is a favorite place for the origination of sudden stratospheric warmings (SSW's), a phenomenon that involves rapid warming in the stratosphere that then allows unusually cold air to reach the surface and lower latitudes just a couple of weeks later. Last winter, we saw a magnificent SSW originate from the Bering Sea, and other warmings attempt to take place in that same vicinity. With positive height anomalies stationed over the Bering Sea, intrusions of warm air by these positive height anomalies into the Arctic are more easily accomplished, thus increasing the likelihood of SSW events. Both my analog set and the other three years are steadfast on strong Bering Sea high pressure, meaning the chances of stratospheric warming events are enhanced, thus leading to higher chances of cold weather.


4. Low Pressure in Eastern North America 
Both images show very strong low pressure anomalies across the Central and Eastern US. This comes as a result of the ridging in the Bering Sea/North Pacific and another significant high pressure anomaly in the Atlantic (for my analogs, it's over Greenland; for the other three years, it is in the north Atlantic). The most significant result of these negative height anomalies over the Central and East US is very cold temperatures, and these are seen in the last image on the picture at the top of this post, as well as in my analog set, shown below:

Andrew

Wednesday, August 14, 2013

Prospects of an Early Winter Quickly Rising

The prospects of an early winter arriving in the United States are rising, as model guidance and observed temperatures in the Arctic support a quick start to the season.

Model guidance is projecting snow cover to begin building over Canada in just several days, and intensifying towards the US/Canada border by the final days of September. Three of the four CFS ensemble members project snow cover extending across much of Canada by the end of September, but all four members are in agreement that snow cover will be building across Canada in just a week or two, and beginning its advance towards the United States by September

Aiding in prospects for an early winter is the continued observance of below normal temperatures in the high Arctic region. As the graph shows, observed temperatures have been strikingly below normal for several months now, and have recently dropped below the freezing level. If below freezing temperatures can be maintained, and the general below-normal temperature trend holds going through fall, I do not see why scenarios like an early snow pack building over Canada and Siberia are unfounded, and thus the idea of an early start to winter over the US is brought to light.

Just because this winter may start rather early does not mean the winter as a whole will be intense; recall the October snowstorm that hammered the Northeast just a couple of years ago, but then saw the rest of winter with below normal snow and above normal temperatures.

Andrew

Tropical Storm Likely to Hit United States; TX, MS, AL Threatened

It now appears that a tropical cyclone (most likely of tropical storm status) will make landfall on the United States. Among the threatened areas are Mississippi, Alabama, and Texas. Mexico is also bearing some threat of this cyclone making landfall in that country.

At this moment, it appears we will see development of this cyclone occur just north of the Yucatan Peninsula. All model guidance that is portraying TC formation does indicate it would begin in that region. From there, model guidance diverges into two clear paths: one takes the cyclone and hits Mexico or southern Texas, while the other path allows the cyclone to travel north and hit Mississippi/Alabama, and possibly a bit of Louisiana. I outlined the TX/MX landfall idea as the more likely one, mainly because of what happened recently over in Asia with Typhoon Utor. There is a theory that if a typhoon in the west Pacific does not curve away from land before landfall, a tropical cyclone in the Atlantic will also refrain from making a curve north, thus enhancing landfall potential. Since Utor did not make a curve north before hitting Asia, I anticipate we will not see a strong curve/shift north like the GFS is showing. Rather, the CMC may have the correct idea of a more west/WNW direction with this cyclone. It should be noted that model guidance is leaning towards the MS/AL landfall more than the TX/MX landfall idea, so please keep an open mind on both solutions; better to be safe than sorry.

Regardless of what happens, it is clear there is a substantial threat to life and property, as is with any tropical cyclone. I personally advise all those living along the coast of the Gulf of Mexico keep a sharp eye on this situation, but heed government notices first and foremost on this landfall threat if any are issued.

Andrew

Sunday, August 11, 2013

Model Guidance Suddenly Threatens Gulf Coast with Tropical Cyclone

The Canadian model's wind speed and sea level pressure forecast for the evening of August 17.

The American model's wind speed and sea level pressure forecast for the evening of August 17.
Model guidance is suddenly projecting a tropical cyclone to develop in the Gulf of Mexico and hit a space anywhere from eastern Louisiana to the Florida Panhandle on August 17th.

As the two images above show, there is remarkable consistency among these two models, with both forecasts having a tropical cyclone making landfall on the United States mainland at the same time (evening hours of August 17). Now, the Canadian (CMC) model is much stronger with this system, which is to be expected- the CMC model is always exaggerating storm forecasts, whether tropical or extratropical. However, with the GFS model now jumping on board with this idea of a landfalling tropical cyclone, it is time we examine just how possible this is.

Global models are indicating we will see an area of enhanced convection in the Atlantic basin, possibly into the Gulf of Mexico over the next 5-10 days. This enhanced convection pulse is timed well with the idea of tropical cyclone formation in the Gulf of Mexico. Adding to this potential is what recently happened in the Pacific waters. We saw a typhoon fail to recurve in the Pacific before hitting East Asia, meaning any tropical cyclone that forms in the Atlantic is unlikely to curve out to sea. As a result, any tropical waves or disturbances coming off Africa are more likely to shift west and thus find themselves entering the Gulf of Mexico.

Current Probabilities

Risk of Tropical Cyclone Formation: 40%
Risk of Hurricane Formation: < 5%
Risk of a Landfalling Tropical Cyclone (in the event a tropical cyclone does form): 80%

Andrew

Saturday, August 10, 2013

Long Range Hints About the Winter of 2013-2014


As I'm putting together my winter forecast (which comes out on the last day of August at 12:00 PM Central), I'm finding that things we are seeing in the late summer/early fall are already providing hints as to what we can expect this winter. Here are a few of them.

1. The Plains could receive the strongest cold over the winter season.
I mentioned this one on The Weather Centre's Facebook Page, and this stems from, among other things tha have brought this theory to the foreground, a favorable pattern in my analog package. After analysis of correlations, the analog package confirms that the mid level atmospheric flow could experience multiple bouts where the jet stream collapses south and engages the Plains in some seriously cold air.

2. The East Coast will see a temperature battle through the winter.
The temperature battle zone for the US will most likely fall along the East Coast through the winter season, as I anticipate increased probabilities of high pressure formation in the waters east of the Mid-Atlantic. Its close proximity to the US will most likely allow propagation of high pressure westward, partially on land, where it will raise the jet stream and permit warmer air to flow north. On the other hand, a rambunctious jet stream will have the tendency to fight the high pressure formation in the Atlantic, leading to a back-and-forth temperature pattern.

3. Nor'easters return in force
It is quite possible we see the emergence of a hyper-active coastal storm regime over the upcoming winter season. As I mentioned in my Preliminary winter forecast, my analog package and long range models remain steadfast on the idea of a strong East Asian jet stream this winter. A stronger jet stream would increase the potential of stormier weather in that area. Using a 6-10 day gap between a significant East Asia storm and an East US storm, the chances of more coastal storms are on the rise. Above normal sea surface temperatures off the East Coast also help these chances.

NOTE: Keep in mind these are only HINTS and do NOT resemble my current forecast at this time. They are subject to change and may very well do so before the release of my official forecast on August 31.

Tuesday, August 6, 2013

2013-2014 Winter Update: Don't Worry, Be Happy

Concerns over a recent switch by the CFS model from showing a cold East US winter to an average/slightly above normal winter are unwarranted, and the main reason why unveils five reasons to be excited about this winter.

The Big Picture
Many people are up in arms over the latest CFS model forecasts for this winter trending from a brutally cold US winter to a rather average, or even slightly above average winter in the temperature department. These are the times when people tend to show a different side- the side that tells a forecaster he/she was wrong about the CFS forecast when they posted how it was advertising a cold winter. People can get particularly nasty towards forecasters who don't deserve it. I posted about the CFS cold trend; luckily, all of you are polite folk who haven't thrown around vulgar comments like I've seen other forecasters get as a result of this sort of situation, when a model suddenly changes its forecasts. But I'm going off on a tangent now. The big picture here is that the CFS really has not changed its forecast as far as the atmospheric pattern goes. While temperature forecasts may have changed, it's pretty apparent that the CFS remains steadfast on a favorable mid/upper level atmospheric flow for the upcoming winter. You will see in the image above that I have five areas of interest numbered from 1 to 5. Each area of interest will be described below.

1. Active East Asian Jet Stream
You will see a tightening of the contour lines in eastern Asia on the image above, under the number 1. This symbolizes the jet stream is under stress, thus increasing its strength in that area. From looking solely at the image above, it would appear pressure anomalies are below normal in East Asia, meaning more storms in that region. If you have been with this blog for a while now, you may recall the times I have brought up a correlation between storms in East Asia and storms in the East US 6-10 days later. If the tightening of the jet stream in E. Asia is due to a stormier pattern in that area, it is entirely possible we see a stormier East US. Let the record show that the CFS has been adamant with this particular item for some time now: November-December-January 200mb forecast from June 2013

2. Ridging Pattern in Northern Pacific
It is well established that the Bering Sea is a favorite place for the origination of sudden stratospheric warmings (SSW's), a phenomenon that involves rapid warming in the stratosphere that then allows unusually cold air to reach the surface and lower latitudes just a couple of weeks later. Last winter, we saw a magnificent SSW originate from the Bering Sea, and other warmings attempt to take place in that same vicinity. With positive height anomalies stationed over the Bering Sea, intrusions of warm air by these positive height anomalies into the Arctic are more easily accomplished, thus increasing the likelihood of SSW events. Once again, this feature has been displayed on CFS forecasts for multiple months now, as the above link depicts. Additionally, bear in mind that these features were in the forecast when the CFS was projecting a very cold winter. In my opinion, it could very well be that the CFS is flopping around with its temperature forecast, as is customary of long range models, while the upper level atmospheric flow really tells the story (i.e. the pattern really is favorable for cold weather, even though temperature forecasts do not reflect it).

3. Ridging Pattern in Western North America
The image at the top of this post displays a widening of contour lines under the number 3. When you get the expansion of these lines, it is typically demonstrative of high pressure anomalies present in the area. The presence of high pressure anomalies in Western Nor. America is defined as a positive Pacific-North American index (PNA) pattern. In response to high pressure in the West US, low pressure (and thus cold air) is favored in the Central and East US. It is also known that a positive PNA results in winter storms taking a track favorable for the Midwest/Ohio Valley to receive snowfall. Yet again, the June CFS forecast identified the +PNA pattern for this winter, just as the current forecast shows.

4. Low Pressure in Eastern North America
This is kind of an extension of Number 3, in the sense of a low pressure response to positive height anomalies across the West US due to the positive PNA pattern. The CFS is picking up on those low pressure anomalies, though the model is reluctant to allow the anomalies to stretch into the United States. My theory on this is that, because the model is showing a forecast averaged out over 3 months, low pressure anomalies/cold weather DOES make it into the US due to the +PNA pattern. The reason why the model may be reluctant to do that on the image above is because we could see high pressure in the Bering Sea work against development of the +PNA pattern, thus preventing low pressure anomalies from reaching the US.

5. High-Latitude Blocking Pattern in Greenland
The image above shows an expansion of contour lines towards Greenland, an indicator that high pressure anomalies are favored in that area. Positive height anomalies in/near Greenland results in the negative phase of the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) is a phenomenon that involves height anomalies across Greenland. In the negative NAO, high pressure is stationed over the land mass in a move that permits cold air and Nor'easter's to affect the Eastern US. On the other hand, a wintertime positive NAO results in a warmer United States with lower probabilities of big snowstorms for the nation as a whole. I brought about the theory that averaging out three months in a forecast may not project the real picture, and that theory also applies here. It applies here in the sense that the NAO may be very negative at times, but may also be less negative during some times. The tendency for a more negative NAO over a less negative/more positive NAO for this three month period in winter may then lead to pressure anomalies averaging out positive over Greenland (a sign of the negative NAO), thus showing an expansion of contour lines towards that region.

As the title of this post says, don't worry, be happy. Concerns over the increasingly-warmer CFS forecast for this winter are unwarranted on the basis that the mid/upper level air pattern has been steadfast throughout the last few months, including the time when the CFS was calling for a brutally cold US. The five points I discussed above have been steadfast in the last few months, and those same five points, when in place during the winter, do tend to set up a favorable pattern for cold and snow in the US area east of the Front Range.

Andrew

Sunday, August 4, 2013

Tropical Cyclone Generation Likely in Caribbean in A Few Days

Ensemble forecasts are indicating the chance of tropical cyclone generation in the southern Caribbean is skyrocketing in the next 5-10 days.

The image above shows the probability of a tropical cyclone forming in the timeframe from 5 days' forecast to 10 days from now. As the graphic above shows, there is higher than a 90% probability that we will see tropical cyclone formation in the waters just north of Panama in this timeframe. Based on the tracks listed on the image, it appears any cyclone that does form in the waters immediately near Panama would drift west and cut through Central America before transitioning to the East Pacific basin.

After the medium range development chance, things still look to be trying to get going. It appears tropical waves coming off of Africa may try to make another shot at development, but we're still a good 2 weeks+ away from that potential.

Andrew

Friday, August 2, 2013

Saharan Air Layer Puts Hold on Tropical Activity


Dry air has moved off of Africa as part of the Saharan Air Layer, resulting in lowered chances for tropical activity over the next several days.

In recent days, an intense layer of dry air has shifted west from Northern Africa, resulting in not only stunning satellite images, but also a decreased chance for tropical development in the eastern Atlantic and for tropical waves coming off of Africa. I anticipate that we should see this outbreak of dry air dissipating over the next week or two, which should allow tropical waves over Africa a better chance for tropical development.

Model guidance indicates chances of tropical development will increase after the 5 day mark from today, which is roughly the time we will see the dry air moving further through the Atlantic and dissipating in the process.

Andrew