Wednesday, July 30, 2014

Fall 2014 Seasonal Forecast

This is the outlook for Fall 2014.

We will begin by analyzing the temperature outlook from a trusted long-range ensemble guidance system.

For the August-September-October period, the ensemble system shows an outlook of warmer than normal temperatures across the Western US and portions of the Northeast, with darker shadings indicating higher confidence in that forecast anomaly. The warmest temperatures appear to be centered over Montana and Idaho in this outlook, as well as portions of New York and towards Maine. The big story here, however, is the anomalous cold shown in this outlook. We see below normal temperature anomalies extending from the Canada/US border, all the way down to the US/Mexico border. The core of the cold looks to be across the Plains and Midwest, with higher confidence in cold weather displayed by the dark blues. These dark blues look to be most prevalent in the Midwest, Plains, Great Lakes, Ohio Valley and Mid-Atlantic.

If we fast-forward to the October-November-December temperature forecast, we find a similar outlook as the one we just analyzed for the August-September-October period. In this forecast graphic, we see cold weather forecasted across most of the nation. The cold extends from the Pacific Coast to the Carolinas, with the deepest cold weather displayed over the North and Central Plains, as well as the Southwest US. Most of the coastal Eastern Seaboard looks to be in slightly above normal temperatures, though confidence in this is rather low.

After a cold winter, spring and summer, a cold outlook for fall is something that makes sense. We are still seeing that persistent pool of warm waters in the northeast Pacific, which has allowed these seasons to be so chilly. As a result, we should be wary of a chilly fall this year, something that could continue into the winter.

Let's now examine the precipitation outlook.

The precipitation outlook for August-September-October from this long range ensemble system has a variety of conditions across the country. We see a general dry trend over the Southwest, unfortunately worsening the already-catastrophic drought in California and other states. The Pacific Northwest is showing a variable signal. The North Plains are exhibiting above-normal precipitation anomalies in rather high confidence for this timeframe, and this trend continues into the Midwest and Great Lakes. A stark dry trend is observed in the Southern Plains with enhanced confidence, and a similar story can be found in the upper Midwest. In the East US, we see mainly variable conditions that cannot let us determine a particular forecast for this area. Beyond this forecast period, the precipitation outlook exhibits too low of confidence to determine a thorough forecast.

Because we don't know what the El Nino situation will do for this fall and winter, it's hard to see how reliable this precipitation outlook is. The drought conditions in the Southwest should allow for a general dry trend there by process of a feedback loop, unless we see a sustained El Nino arise. I do believe we see conditions in the Midwest and Great Lakes a bit drier than they are projected to be, with conditions along the East Coast averaging around normal or slightly above normal.


Monday, July 28, 2014

Updated Thoughts on 2014-2015 Winter Outlook

This post will show my personal thoughts on the upcoming winter. In the past, I've put out posts focusing on one or two mechanisms that may influence the winter, but this article will show you what my personal thoughts are.

We're going to begin with a discussion focusing on sea surface temperature anomalies. We've gone over this quite a bit so far this summer, but I haven't really put my two cents into those posts.

Looking at this chart, I see a few things to keep an eye on. Primarily, the warm pool in the northeast Pacific must be watched closely. In the winter of 2013-2014, we saw persistent ridges of high pressure forming along the West Coast, leading to strong upper level lows dropping south into the Central and East US. This pattern allowed extreme cold to be pumped mercilessly into the United States. The warm pool has not dissipated from last winter to this winter, so my concern for another cold winter automatically rises.
I believe that mechanisms upstream (to the west) of the United States influence the weather pattern more than mechanisms more downstream (to the east), primarily because the upstream factors are almost guaranteed to affect our weather based on their location. A prime example is that ridging due to the warm pool in the northeast Pacific last winter. This allowed for a cold winter. However, the lack of persistent ridging over Greenland last winter would have typically argued for a warmer winter, especially in the East US. Did this happen? No, we still received record-breaking cold. You can point to the upstream location of that warm pool of water as a reason why we didn't see warmer weather prevail. All in all, my point is this winter has substantial potential to be cold once again. If those warm waters persist in the northeast Pacific into the winter months, it's probably a good bet you'll need those extra blankets to keep warm for December through February.

Something that has me concerned, however, is the large presence of warmer than normal water anomalies around Greenland and in the waters around northeast Canada, all the way to Europe. What could happen this winter is that we see persistent ridging in the northeast Pacific, but also in the northern Atlantic. From there, the question shifts to if we will see a persistent upper level low in North America, or not. The lack of an upper level low would likely place the US under predominantly zonal flow, something that would result in a warm winter. However, the presence of a strong upper level low could easily make for relentless cold in portions of central and eastern North America. This isn't subtracting from the overall likelihood of a cool winter based on the water anomalies in the northeast Pacific, but it is something to keep an eye on.

In a way, we haven't really seen last winter's pattern leave us. The image above shows 500mb wind speeds in the shaded regions, with wind barbs and pressure contours spread across the image. This graphic is valid for early this afternoon, on July 28, 2014. Even though it's July, you might notice some similarities to the upper air flow from January 2014. We still see strong ridging over the Western US, and an anomalous upper level low in Canada allowing cold air to dig into the North US. If this pattern continues into the fall months, the chances for a cold winter increase greatly. This is something that will have to be monitored closely.

Refresh this page if the animation stops looping.
The big discussion in the weather world revolves around the situation unfolding in the Pacific. Earlier this year, a record-breaking Kelvin Wave brought about the prediction of a moderate or strong El Nino event for this winter, with calls for Super El Nino-like conditions also being heard (admittedly, from me, too). The Kelvin Wave did hit the surface and brought about significant warming to the eastern Pacific waters. However, as we progressed into summer, these warm water anomalies seemed to evaporate overnight, the culprit seen as the band of below-normal waters about 100 meters down from the surface in the animation above. As of now, we are counting on the mass of slightly above-normal temperature waters in the western part of the animation to push east and hit the surface to make another push at an El Nino. It remains to be seen how this will all play out. One possibility is that the warm waters can hit the surface and induce a weak El Nino event. Another possibility is that the cold waters eat away at the warm waters and eliminate the chances for an El Nino this winter.

My current thoughts on the matter are that we are likely to see a weak El Nino this winter. The dissipation of the strong Kelvin Wave has left us with nothing to support a moderate or strong El Nino, so the most likely scenario is a weak El Nino, if we are to see one at all. I'm uncertain as to how those cold water anomalies will react to when/if the warm waters push east; it'll be something to monitor closely this fall. When all is set and done, however, I'm supporting a weak El Nino. A weak El Nino set-up would resemble something like this, as the image below shows.


To summarize:

I expect that we see a cooler than normal winter for many across the North US, primarily the Great Lakes, Upper Midwest, and Northeast. This comes as a result of the warm waters in the northeast Pacific, as well as the expectation for a weak El Nino. Temperatures should be warmer in the West US once again. I do think we see the drought in the Southwest US ease up at least a bit, but until we can nail down the presence (or lack thereof) of an El Nino, it's up in the air.
Precipitation looks to be on the above-average side around the Great Lakes again, thanks to lake effect snowfall, with the same outlook pegged for the Northeast. This comes from the warm waters off the East Coast likely interacting with cold air from Canada to produce the chance of precipitation. Conditions in the South Plains and Gulf Coast are likely to be slightly wetter than normal, with the opposite anomaly predicted for the North Plains. The Midwest and Ohio Valley ought to see around normal anomalies, as things look right now.

Bear in mind this is not my final forecast. It is merely an update with my personal thoughts, in advance of the 2014-2015 Official Winter Forecast to be issued in October.


Saturday, July 26, 2014

Extensive Damaging Wind Episode Expected Today

A severe weather episode, comprised of tornadoes, large hail, and potentially extensive damaging winds, will take place today.

The Storm Prediction Center has issued a Moderate Risk of severe weather for a portion of the Midwest, including much of central and southern Illinois and southwest Indiana. A Slight Risk of severe weather extends from extreme southeast South Dakota to far western West Virginia. It is expected that a swath of severe thunderstorms, capable of damaging winds, as well as an isolated tornado, will traverse the aforementioned risk areas. The Moderate Risk outline highlights areas where the threat is greatest.

The above outlook is superimposed on the latest infrared satellite imagery on the graphic shown here. On this graphic, we see a complex of thunderstorms moving into Iowa from South Dakota, sending cloud cover off to the east into the Great Lakes, likely limiting any severe threat that was there to begin with. We also see clouds in the western half of the Slight Risk area, and this is something that has been limiting instability so far today. Unless that cloud cover evaporates fairly quickly, I am concerned that severe weather will not be favored for Iowa, Nebraska, Missouri, and western Illinois. On the other hand, the Moderate Risk area is experiencing only sporadic cloud cover, with much of that area cloud-free. This re-assures me that severe weather is still expected today, and this is confirmed by rising instability values over that cloud-free zone.

Those in the Moderate Risk area today should prepare for the following:
• An isolated tornado or two.
• Large hail, possibly damaging to vehicles and property left outside.
• Damaging winds, potentially on a large scale, with significant damage possible in some areas.


Wednesday, July 23, 2014

Current Water Temperatures Support Southeast Ridge Next Winter

Current sea surface temperature anomalies are supportive of the dreaded Southeast Ridge making an appearance next winter.

The image above shows sea surface temperature anomalies from July 11, 2014 to July 18 2014, projected across North America. In this image, we want to focus on the anomalies around the Southeast United States and up through the East Coast.

We see a general presence of slightly to well above normal sea surface temperature anomalies when examining the waters to the west and east of Florida. In those regions, we can observe widespread anomalies over one degree K above normal. Looking up along the East Coast, we see these warmer than normal anomalies still present, though not as intense as those near Florida and the Bahamas.

While this feature may not be as significant when compared to those features in the Pacific, it does hold substantial weight when analyzing the expected climate of the United States this winter. Depending on a multitude of conditions in the atmosphere, there is the potential for a semi-permanent ridge of high pressure to form in the Southeastern United States during the cold season. The durability and strength of this ridge varies on a case-by-case basis, but its presence can never be overlooked when it appears. The ridge allows the storm track to be deflected northward, sometimes bringing winter storms into the Plains if the ridge is strong, and other times into the Midwest and Ohio Valley if the ridge is weaker. What is clear, however, is that this phenomenon spells bad news for winter weather fans residing along the East Coast. This ridge almost always delivers warm, quiet, snow-less weather to those in the East. Unfortunately, if the latter description sounds like you, the chances of these conditions arising this winter have been raised.

The winter weather fans in the East Coast may not want to hear this news, but those in the Plains and Midwest should thoroughly enjoy this latest news, even if it may just be a flash in the pan. We'll have to see how the El Nino situation evolves this fall, hence the flash in the pan reference.


Tuesday, July 22, 2014

Weak Upwelling, Hostile Environment Could Spell Weak El Nino Ahead

A weak episode of upwelling in the eastern Pacific, combined with a continued hostile environment with respect to El Nino formation, could indicate that a weak El Nino may be in store for the future, rather than previous projections of moderate and strong El Ninos.

Michael Ventrice
Shown above is what the concepts of upwelling and downwelling look like. Imagine, for a moment, the eastern Pacific is completely flat, no perturbations or disruptions in the surface or underwater currents. Imagine that the western portion of the water begins to rise. In the Pacific, Kelvin Waves can propagate from west to east along the Equator, bringing about a rise in sea surface temperatures and in the actual water height. As a result, we see water levels in the east drop ever so slightly, likely not even recognizable. As time progresses, in the Pacific, the Kelvin Wave will eventually push east, and the warm waters will push to the surface. As the third panel shows, this sort of motion is referred to as "upwelling", where the subsurface waters push to the surface. In response, a body of water nearby (in this case, the Central Pacific) will exhibit "downwelling" characteristics, where water temperatures will either warm or cool, the opposite temperature anomaly as the anomaly involved in the upwelling incident.

If that was confusing, don't worry, we can explain it better below.

The image above shows the anomalous depth of the 20º Celsius isotherm below the surface in the eastern Pacific. In layman terms, positive anomalies on the chart above mean warmer than normal waters, while negative anomalies mean colder than normal waters. Check out how we've seen a series of cold and warm episodes across the Pacific in the last year. In October 2013, we saw cooler than normal water temperatures shift east with time (hence the slanting down and east with time (left legend) and direction (bottom legend)). In an interesting correlation of how upwelling episodes seem to determine the strength of the following downwelling episode, we saw warmer than normal waters follow quickly in its footsteps around November 2013. This was a classic example of upwelling and downwelling. We saw upwelling occur with the below normal waters in October, as cooler waters were brought from underwater to the surface, and the resultant downwelling episode occurred in November, when surface-originated waters were forced underwater and eastward. We saw an even stronger occurrence of this in January 2014, when upwelling occurred, and then our historic Kelvin Wave induced the upwelling in February and March 2014.

So, it would only be natural to expect an even stronger upwelling phase now, right? Wrong. Looking at that chart above, now that our Kelvin Wave has passed, we see barely any evidence of sustained upwelling. If we consider that the strength of the upwelling episodes (cool anomalies) could actually predict the strength of the downwelling episodes (warm anomalies), one might think that the upcoming downwelling episode may result in more of a weak El Nino than one of a stronger magnitude. Although the correlation discussed isn't exactly how the upwelling/downwelling episodes work, it's worth seeing if such a correlation might be even remotely successful at predicting the upcoming El Nino.

The El Nino has been difficult to come by. This most recent Kelvin Wave, expected to bring us that strong El Nino, couldn't hold its ground and ended up dissipating. Add to that the atmosphere never exhibited El Nino characteristics, and it's all-around bad luck. Some change is on the way, however.

Kyle MacRitchie
The image above shows the long range forecasted MJO phase from the CFS model, from Kyle MacRitchie. This forecast has the Madden Julian Oscillation moving into Phases 8, 1 and 2 by the early and middle parts of August. In simpler terms, this forecast suggests that we will see enhanced convection over the western portion of Oceania and around the Indian Ocean in August. Why is this important? When we see tropical convection in those areas, the atmosphere can respond by pushing this convection eastward into the open Pacific, possibly as far as into South America. If this convection can reach the Indian Ocean and around Oceania, it can create westerly winds from that area into the east Pacific, setting up a favorable environment for El Nino formation. If the convection can actually move into South America, the potential of El Nino-like conditions forming greatly rises. The gist of all of this is, the tables could be turning in favor of an El Nino, after a long time of suffering quite an uphill battle.

To summarize, the upwelling-downwelling pattern we discussed earlier tells us that only a weak El Nino could be in the cards down the road. However, after examining the projected placement of tropical convection in the Indian Ocean, El Nino formation could actually be favored, even if it's only favoring a weak or possibly moderate El Nino (I would place my bets on the former option, however).


Monday, July 21, 2014

First Full Winter Forecast from Long Range Climate Models Released

The first forecast encompassing the entirety of the 2014-2015 winter season has been released from the major long range climate models. Today, we will discuss the three-month averages of temperature and precipitation anomalies. Future posts will break down these averages into month-by-month increments.

The first graphic we will look at shows temperature anomaly forecasts averaged out over December-January-February. In this image, we do see a variety of solutions, with the majority of them supporting a warmer than average winter. The CFSv2 model, the long range forecast from the American weather services, inundates Canada and the United States with a well-above average winter. Only Mexico is safe from the extreme warmth here. The two Canadian weather service projections, labeled CMC1 and CMC2, show different projections. The CMC1 forecast keeps most of the nation warmer than normal through February, only sparing the Four Corners region in the United States, while the CMC2 projections has much of the Central and East US in below-normal temperatures for the winter. Alaska and western Canada look to experience warm weather. Rounding out the top row, the GFDL_FLOR, a version of another American model, has the Plains/Rockies in for a chilly winter, while keeping the North US warm.

Along the bottom row of forecasts, we begin with the GFDL model, a variant of the GFDL_FLOR model we just analyzed. This forecast keeps most of the nation warmer than normal during December, January and February, though a cool reprieve is given to those in the south-central Plains. The NCAR model, another American climate model system, turns on the oven for the Lower 48 while locking Alaska and northern Canada in the freezer. A variant of this NCAR model, the NCAR_CCSM, has nearly all of North America seeing warm readings on the thermometer this winter. Lastly, the NASA model, yet another American-based forecast, shows a cold Central & East US winter, with a warm West Coast, not unlike what we saw last winter.

As for precipitation, the picture is much less clear. The CFSv2 model has a dry Pacific Northwest and New England, but finally brings wetter conditions to the drought-stricken Southwest and South Plains. Additional wet weather continues into the Gulf Coast region. The CMC1 has a snowy winter for the Great Lakes while continuing the above-normal precipitation trend in the Plains, but the CMC2 model brings this moisture to the Ohio Valley, leaving the Pacific Northwest with the driest outlook. The GFDL_FLOR resembles the CFSv2 forecast, drying out the Pacific Northwest, moistening up the Southwest and South Plains, but this time extending this moisture into the East Coast.

Along the bottom row, the GFDL model has a nightmare forecast of wet conditions in Oregon and Washington state, resulting in yet another dry winter for California and the Southwest. Texas and the southern Plains see their winter forecast with added precipitation, but negative precipitation anomalies hold over the Ohio Valley and Northeast. For the NCAR forecast, the entire West Coast observes a very wet winter, also seen in the Eastern US. Only the Central US is kept out of this above-normal precipitation inundation. The NCAR_CCSM forecast brings above normal precipitation to nearly everyone in the Lower 48, except for the Pacific Northwest. Lastly, the NASA model has a very dry West Coast winter, reciprocated along the Midwest and Ohio Valley. Wetter than normal conditions are observed along the Gulf Coast.

Breaking it down, I want to first throw out the NCAR, NCAR_CCSM and NASA model forecasts, as they are known to exaggerate anything they forecast, and generally retain a very poor track record. I feel the general consensus of climate models is too warm, mainly because the primary factor that brought us a cold winter last year is still in place today. I realize that this factor can't control the entire atmosphere, but if anything's going to have a synoptic impact this winter season, it'll be the warm waters in the Northeast Pacific, bringing cold air down south from Canada into the US.
It is rather likely we will see a wetter than normal Southwest, South Plains and Gulf Coast, but beyond that, precipitation anomalies for other areas of the United States are in question. I'm not confident in the East Coast snowy anomalies, nor the both positive and negative anomalies seen across the Midwest and Great Lakes. We will need more time to figure that portion of the forecast out.


Saturday, July 19, 2014

'Death Ridge' to Make First Appearance This Summer

The infamous ridge of high pressure which frequently forms over the Plains in the summer months, nicknamed the 'Death Ridge', will be taking up position this week for the first time this season.

The above image shows forecasted 500mb height contours, wind barbs, and wind speeds in the shaded colors. The forecast image comes from the ECMWF model, and is valid on Wednesday evening. Here, we see a body of strong high pressure originating in the Four Corners region, at a strength of about 597dm, as the contour shows. We see the ridge extending well into Canada, setting up sustained northwest flow over the Midwest and Great Lakes in the process.

Model guidance agrees that we will see multiple disturbances traversing the northern fringes of this ridge, swinging up into Canada and eventually down into the Great Lakes, towards the Ohio Valley. As the systems swing down into the Great Lakes, I expect we will see opportunities for severe weather. These opportunities could be plentiful, depending on the number of disturbances expected to rotate along the perimeter of this large high pressure system.

The GFS model's forecast of the Lifted Index, shown above, also valid on Wednesday evening, gives a good idea of where we might expect some active weather to form. The Lifted Index gives forecasters the ability to see how unstable the air is. Negative LI values indicate increasingly unstable air, and values below roughly -6 can indicate the potential for some substantially active weather. In this forecast image, we see LI values in portions of Ohio and Indiana exceeding -12, highlighting the presence of extremely unstable air. Considering this is a low-resolution model, it could very well be exaggerating how unstable the air will be. Nevertheless, this is a testament to what we may see next week, when some parts of the Central US may be affected by severe weather.

Lastly, we see the GFS forecast for temperatures just a few thousand feet off the ground on Thursday evening. This image gives one example of the areas expected to be hit the hardest by this hot weather, with portions of the Rocky Mountains into the Plains on the receiving end of the worst weather. If you live in the aforementioned regions, prepare for this hot weather by stocking up on water for you and your pets, as well as limiting outdoor activity and making sure your air conditioning unit is up to par.


Wednesday, July 16, 2014

Long Range Climate Models Show Snowy Eurasia in October

Long range models are giving indications that the coming October may feature above normal precipitation in the Eurasia area, something that could then favor a colder than normal winter for the United States.

The image above shows a global probability of above, below, and neutral precipitation anomalies. We can focus in on many areas of the world and try to decipher what they mean for the coming winter, but today, we’re going to keep our attention on the forecast over Russia and the general north Asia area.

This forecast, a probability forecast using a combination of roughly six or seven different climate models from various global meteorological agencies, shows a swath of above normal precipitation probabilities across a good portion of central Russia. In the forecast, we see the precipitation anomalies extending north of the 60N longitude line, an important line in our situation.

A few years ago, Dr. Judah Cohen created the Snow Advance Index, abbreviated as the SAI. Dr. Cohen claimed that by measuring snow cover anomalies in Eurasia, namely north of the 60N parallel, one could decipher temperature anomalies for the upcoming winter. For example, an October with sustained below-normal snow cover anomalies would favor a warmer than normal winter. Similarly, above-normal snow cover in Eurasia for the month of October would then tell us to anticipate a colder than normal winter. In past winters, I have seen the SAI perform quite well, the only exception being this past winter. Thus, I hold this index in fairly high regard in terms of accuracy.

As of now, guidance does favor a wetter than normal October over Eurasia, with some of that likely putting down snow cover in the process. While this is expected to change in the future, this could be an indication that we may expect a snowy October in Russia, which may lead to a colder winter here in the United States.


Tuesday, July 15, 2014

2014-2015 Winter Forecast Update; Colder Outlook Now Favored

This post will examine the factors being analyzed for the upcoming winter, their impacts on the cold season, and anything that may have changed from the issuance of the Preliminary 2014-2015 Winter Forecast to today.

After going over the factors presented in our Preliminary winter forecast, and examining new data presented to me, I’m electing to favor a colder outlook to this winter, over the original warmer projection earlier this summer.

The above image shows observed sea surface temperature anomalies across the globe from July 1, 2014, to July 8, 2014. In this image, we notice three particularly interesting features. One of these features is the pool of well above normal water temperatures in the Northeast Pacific into the Gulf of Alaska. This particular mechanism is one of substantial importance, given it also played a significant role in our last winter.

In the winter of 2013-2014, we had this warm pool present throughout the entire season, and it was quite possibly the most influential factor in making that winter as cold as it was. The warm water enabled strong high pressure to form over the Northeast Pacific, something that is continuing even to this day. See the examples below.
The image above shows mid-level geopotential height anomalies in early January 2014. Cold colors indicate the presence of strong low pressure, hence below normal temperatures. The yellows and reds indicate high pressure, and warmer than normal weather. This image was recorded in the middle of the extreme cold spell that kicked off the new year, also spawning the ‘polar vortex’ hype. In this graphic, we can see the polar vortex located somewhere in south-central Canada, bringing that extreme cold to much of the United States. We also saw strong high pressure centered over Nova Scotia, and quite extensive high pressure from the Southwest United States to Alaska. It was this second body of high pressure that formed as a result of those aforementioned warm waters in the northeast Pacific, and we saw this ridge stay in place consistently throughout the winter. Now, with the warm waters in the Gulf of Alaska still in place a good year later, I am significantly concerned with the idea that we could see this extensive ridge forming yet again this coming winter.

Building off of this idea, in addition to the water temperature pattern in the Pacific going relatively unchanged since last winter, the upper air flow has remained relatively unchanged as a result.

Tropical Tidbits
This forecast image, valid on Monday, July 14, shows the same 500mb geopotential height concept that we saw earlier in this post, with blues indicating low pressure and reds indicating high pressure. In this forecast image, once again, we see strong high pressure stretching along the western coast of North America, with another body of high pressure being observed over Nova Scotia and far eastern Canada. And in a situation just like the polar vortex plunge last winter, we see anomalous low pressure crashing into the United States. This upper air pattern is almost (keyword almost) exactly like the one we saw last winter, bringing into question if we could see this pattern persist into next winter as well. In my opinion, if the sea surface temperature anomalies remain the same into next winter as they are now, I see no reason to discount the idea that the coming winter could be like last winter; a cold, potentially brutal one.

Adding to the pieces of this puzzle is the body of significantly above normal temperature anomalies near Greenland. This is a change in what we saw from last winter. This past cold season, we observed primarily below-normal water temperatures near Greenland, resulting in some very stormy periods in the northern Atlantic. However, now that we’ve entered July, we now find ourselves with a formidable body of positive water temperature anomalies, something likely to change the game for the coming winter.

When warmer than normal water temperatures exist near Greenland, it provides a similar opportunity to that in the northeast Pacific, where high pressure can form. In this instance, high pressure can form over Greenland, and actually force the jet stream to buckle in the East US, resulting in an influx of colder than normal air to that area, as the image below shows.

 We didn’t have that warm water in place last year, meaning such a sequence of events couldn’t happen often, if at all. However, now that the anomalies have reversed, we’re in a much better position to see the jet stream buckle more frequently over the East US, resulting in another cold winter.

On a side note, we also see persistent above normal water temperatures near Nova Scotia, which could provide the mechanism needed to create high pressure in that area. This could then combine with the warm SSTs in the northeast Pacific to create an environment very similar to the one observed with the polar vortex incident.

We now continue on with a look at temperatures in the Arctic Circle. The graph above shows observed temperatures in Kelvin over the Arctic Circle (colored red), from the first day of 2014 to present day. We also see a green line, indicating the average Arctic Circle temperature for that given day, allowing us to compare with the observed temperatures to detect any anomalies. The consistent blue line highlights the freezing temperature mark. On this image, we see Arctic temperatures have been steadily below normal this summer, something that does not bode well for us in North America.

In order for winter to even be cold to begin with, one needs cold air. It seems simple to understand, but now we need to understand where this cold air will come from. By using this graph above, we can get an early glimpse at how much cold air the upper latitudes may be storing up for this winter. In this instance, below-normal Arctic temperatures in the summer might tell us to prepare for a cooler than normal winter ahead, while a warm Arctic summer could indicate a warmer winter ahead. Going by this guideline, we might be best off preparing for a chilly winter.

Now, last but definitely not least, we will go over the evolving situation in the Equatorial Pacific.
The image above shows equatorial upper-ocean heat anomalies, in Celsius. This means that the temperature anomaly for the upper portion of the Equatorial Pacific is calculated, giving a helpful indicator to the state of the El Nino-Southern Oscillation (ENSO) phenomenon. In this case, positive anomalies indicate the presence of warmer than normal waters, and potentially an El Nino. Similarly, below normal upper ocean heat anomalies highlight below normal water temperatures, potentially also the presence of a La Nina.

Looking at this graph over the past year, particularly since February 2014, we see that the upper ocean heat anomalies have skyrocketed, up to abut 2.0º Celsius above normal in late March 2014. It was at this time that we were expecting a strong El Nino to evolve for the coming winter. Things have certainly changed since then. The warm waters began to hit the surface this past spring, but couldn’t hold their ground, per se. As a result, we have seen the positive anomalies drop off to neutral territory, indicating that any possible El Nino no longer theoretically exists. Time will tell if we see another body of warmer than normal water temperatures pushing to the surface, possibly creating an El Nino. If that does not happen, we can expect the winter pattern to be dominated by more mesoscale (smaller-scale) features, such as the bodies of warm water temperatures in the northeast Pacific and around Greenland. This could then lead us into - you guessed it - a cold winter.

All of this is expected to change as we progress through summer and into fall; this is merely an update to the situation, since many things have changed since the initial issuance of our Preliminary 2014-2015 Winter Forecast.


Thursday, July 10, 2014

Upcoming Winter Shaping Up Similar to Last Winter; 2014-2015 Could Be More Severe

Note: The idea of this winter being more severe than last is a preliminary finding based on the work presented in this post. It is by no means set in stone, and is subject to revision.

After a look back at July 2013, I'm finding that July 2014 sea surface temperature anomalies are not only similar to last July, but could be foreshadowing a more severe winter than last.

Shown above is a reanalysis image of sea surface temperature anomalies from July 1, 2013 to July 8, 2013. During that timeframe, we saw a large body of warmer than normal waters controlling the northeast Pacific into the Gulf of Alaska, even stretching down towards the coastal waters near southern California. We also saw a pocket of well above normal water temperatures west of Japan, with opposing cooler than normal waters to the east. We also saw the La Nina-like water pattern along the Equatorial Pacific, which helped keep us in a Neutral-ENSO winter for this past cold season. Transitioning to the Atlantic, we saw a snaking line of below normal SST anomalies, occasionally interrupted by small bodies of positive water temperature anomalies, which were mainly confined to the northwestern Atlantic.

Now, let's compare all of that to what we've seen so far this year.

The image above now shows sea surface temperature anomalies, still on the same intervals, but now valid from July 1, 2014 to July 8, 2014. Looking to the northeast Pacific, we see that the large body of above normal-temperature waters has not only persisted, but has now intensified and expanded its influence. This was a major factor in last winter's atmospheric flow, and I don't expect things to be any different this winter. We now see the Bering Sea flooded in warmer than normal waters, though just what impact this particular feature may have is unclear right now. We see a similar opposing water temperature pattern to the west and east of Japan, though a substantial change in the Equatorial Pacific is the presence of warmer than normal water temperatures as opposed to the below normal temperatures last year at this time. This would typically indicate the presence of an El Nino, but with uncertainties as to if it will sustain itself, and if the atmosphere will actually "recognize" the presence of an El Nino, some things still need to be sorted out.

Now that we've gone over the similarities, why am I thinking that this winter could be more severe than last?

1. Above Normal Water Temperatures in the Northeast Pacific
Last winter, we experienced extreme bouts of cold, many of which were due to the proximity of the United States to the polar vortex, a massive, semi-permanent low pressure system stationed over the Arctic Circle. The polar vortex was persuaded to dip south into North America, thanks in large part to a massive ridge that constantly formed and re-formed along the west coast of the continent. Because the jet stream went up with the ridge pushing northward, it had to also dip down somewhere, and that somewhere became the United States. The big ridge originated from the body of warm waters in the northeast Pacific last winter, which is why I'm so concerned seeing that mechanism still in place today. If those warm waters stay in place in the northeast Pacific into the winter, they could make that big ridge re-appear, possibly stronger than last winter, leading to an even colder winter this year.

2. Above Normal Water Temperatures near Greenland
Something we didn't have last winter was a swath of above normal water temperatures near Greenland. This prevented high pressure from forming over that area, something that would have raised the chances of an even colder winter than what we ended up seeing. This year, as the July 2014 SST image shows, we do now have a large body of above normal SST anomalies near Greenland. This significantly raises the potential of high pressure forming in that area, buckling the jet stream to the west and resulting in an even colder winter possible. This is just another mechanism I'm watching this winter that could cool down the temperature forecasts even further.

Whether all of this ends up happening, or doesn't happen at all, is yet to be seen. The point is, based on sea surface temperature anomalies, this year is looking a lot like last year at this time. And according to preliminary looks at some key SST anomaly features, things could be more rough than last winter.


Midwest, Ohio Valley Threatened by Significant Cold Blast Next Week

The upcoming cold blast is expected to drop temperatures into levels more akin to those observed in the fall season.

The Climate Prediction Center's 6-10 day temperature anomaly outlook shows significant warm temperature anomalies, centered over Washington, Oregon, Idaho and Nevada. These warm anomalies look to be produced by strong high pressure building up across the West Coast into Canada. As a result of this strong ridge, a strong low pressure system looks to drop south into the United States. This system looks to be the summer version of the infamous polar vortex, and even though the harsh cold is reduced due to the summer season, anomalous cold is still expected. For this reason, we see below normal temperature anomalies stretching from Montana to the Atlantic Ocean, maximized over Minnesota, Wisconsin, Michigan, New York, Pennsylvania, Ohio, Indiana, Illinois and Iowa. These aforementioned states could see temperatures drop into the low-40s, or even an isolated upper-30 degree reading.

Drag me to storm models
On the morning of July 16th, we see the cold blast taking hold over much of the country. Lows below 60 degrees extend from Montana to North Dakota, down to Kansas and West Virginia. We then see the core of the cold slamming the Plains and Midwest, where lows in the 40s can be expected in many spots. Towards the Great Lakes in the Upper Peninsula of Michigan, lower-40s may be possible.

Drag me to storm models
By the morning of July 17th, the cold is beginning to recede from the western Plains, but is only intensifying in the Ohio Valley. We still see lows around the mid-40s around Iowa, Minnesota, Wisconsin and Michigan, with lows flirting with 50 degrees closer to Missouri, Nebraska and Kansas. The coldest weather now stretches into the Northeast, with states like Pennsylvania, New York, Vermont and New Hampshire experiencing lows deep into the 40s. The mountainous regions of West Virginia could actually see lows nearing 40 degrees, or even into the upper 30s.

Make sure any sensitive outdoor plants are prepared for this cold blast, as damage could be done due to the longevity and pure anomaly of this cold weather event.


Tuesday, July 8, 2014

Unseasonable Cold Blast Looming; Pattern Similar to Last Winter

An unseasonably cold airmass looks to wash over the northern United States, in a pattern eerily similar to the one seen this past winter.

The Climate Prediction Center's 6-10 day temperature outlook shows significantly above normal temperatures across the West US, most severe over Washington, Oregon, Nevada, Idaho and California. In response to this warmth, we see a deep airmass of unseasonably cool temperatures pushing south across the Midwest, with states like Minnesota, Wisconsin, Illinois, Iowa, South Dakota, Nebraska, Kansas and Missouri all affected on the highest level. Warmer than normal weather looks to retreat to the Gulf Coast and coastal regions along the Eastern Seaboard, but the main story here is indeed the colder than normal weather.

Drag me to storm models
Shown above is a long range forecast of temperatures on the morning of July 15th, in the middle of this unusually cold spell. We see temperatures on this morning plummeting to as low as the mid-40s in the Midwest, where the heavy blankets might need to make a surprise appearance. Temperatures in the far northern Plains into the upper Midwest might even flirt with the low-40s, possibly even into the upper-30s if there will be clear skies. Those finer details will need to be ironed out in days to come, but the general idea is that things are looking pretty cold for a wide swath of the country in the next week or two.

Oddly enough, the atmospheric pattern behind this expected cold blast is quite similar to the pattern we observed this past winter. On the top-left image, we see the mid-level atmospheric flow valid on July 14th. Here, we can see a strong vortex dropping anomalously south from Canada, nearly pushing into the United States. If you recall, we had the polar vortex take a very similar path down south more than once last winter, which is how the weather got so cold so often. So what's provoking this to happen again, only this time in mid-July? The same thing that made it happen six months ago. We see a very strong ridge pushing north across the northeast Pacific and into the Gulf of Alaska, which is how the West US should end up with those much warmer than normal temperatures. And, bringing things back full-circle, that ridge is likely being caused/enhanced by the body of above-normal water temperatures in the Gulf of Alaska that we targeted as the mechanism responsible for the brutality of last year's winter. The latest water temperature anomaly image is shown below, which identifies the body of much warmer than normal water in the northeast Pacific.


Monday, July 7, 2014

El Nino in Serious Trouble; Upcoming Winter In Question

The El Nino that has been widely discussed across the meteorological community appears to be in serious trouble.

If we look at a graph of upper-ocean heat anomalies, one way to measure the water temperature anomalies near the surface, we can see the evolution of the projected El Nino this past spring. We see how heat anomalies soared as Kelvin Wave-induced warm waters began hitting the surface after posting record-breaking numbers underwater weeks earlier. However, beginning in May, we began to see heat anomalies drop off, and it is only recently that we have seen oceanic heat anomalies plummet to levels that indicate the El Nino is no longer present. This comes as a shock to the system, after we observed that record-breaking Kelvin Wave this past spring.

Refresh page if animation is not looping
An animation of water anomalies on a depth-by-latitude chart reveals this dramatic reversal of water anomalies in the Pacific. We saw how the record-breaking Kelvin Wave began hitting the surface in May, but from there, cooler than normal anomalies are seen about 100-150 meters down just eating up the warmth. Now, as we start off the month of July, we find ourselves with barely anything to hang onto that would allow us to call this a potential El Nino.

All of this brings the upcoming winter into question, creating what could be a whole new ballgame. If this El Nino fails to form, which is becoming more and more of a possibility with each passing week, we're looking at a drastically-altered landscape in terms of expected precipitation and temperature anomalies over North America. 

This situation will be revisited in coming weeks.


Saturday, July 5, 2014

Severe Weather Discussion for Sunday, July 6th

Severe weather is possible on Sunday, July 6.

The Storm Prediction Center has highlighted portions of Wisconsin, Minnesota, Iowa, Illinois, Indiana, and Missouri for severe weather on Sunday. Within the aforementioned regions, northwest Illinois, Wisconsin, northeast Iowa, and extreme southeast Minnesota look to have the highest severe weather potential.

Projections of convective available potential energy (CAPE), a measure of how unstable the atmosphere is projected to be for Sunday night, give away the reason the aforementioned states have an elevated risk. We see CAPE values exceeding 5000 j/kg over Iowa and Wisconsin, nearly encompassing the entirety of that 30% severe weather risk area. It is apparent that high instability will be the focal point of Sunday's severe weather event. While the highest threat should remain over IA/IL/WI, I'm seeing continued high instability readings across Missouri and Illinois, areas that should also see some active weather tomorrow.

I am concerned that convection in northern Illinois and southern Wisconsin may not be fully realized after analyzing projected atmospheric soundings. Soundings valid for Sunday evening show that temperatures needed for thunderstorms to form in northern Illinois will need to break into the low 90s, even though the high temperature in Chicago is projected to be 88. I do believe active weather will go through these regions, but I wanted to voice my concerns of a potential letdown, per se, of any potential severe weather in these areas.