Tuesday, January 9, 2018

January 12-14 Potentially Significant Winter Storm

A potentially significant winter storm is expected to impact the Ohio Valley and Northeast in the January 12-14 period, with all modes of wintry precipitation possible.

As of this morning, a strong upper level low was located offshore California, moving into the Southwest. As discussed in a previous post about the January 10-12 Winter Storm, this upper level low will actually be torn into two pieces by January 11th, as a piece of energy currently skirting the U.S. / Canada border near the Pacific Northwest will help a portion of the upper level low to become negatively-tilted and create the winter storm over the 10th through the 12th. This process is shown below.

As this piece of the low is taken northward and creates that winter storm, however, a deep positively-tilted trough is left behind in the southern Plains. This will be the energy that creates the January 12-14 potentially significant winter storm, expected to primarily affect the Ohio Valley and Northeast with wintry precipitation.

By Friday evening on January 12th, the aforementioned energy in the southern Plains is forecasted to move east into the Southeast and strengthen, to the point that it becomes negatively-tilted (shown in the northwest-to-southeast orientation of the vorticity maxima), indicating a mature storm system at peak / near-peak strength.

Tropical Tidbits
A few hours before that image is valid, the surface low will have already formed and is projected to be near eastern Tennessee by Friday afternoon. The swath of warm air that the January 10-12 Winter Storm had to deal with will again be present in the Northeast, allowing this event to begin as rain for the entirety of the Northeast and portions of the Ohio Valley. Northern Ohio and portions of Indiana may be able to retain temperature profiles cool enough to support wintry precipitation for nearly the entire event, but I have a feeling that will be more of a "nowcasting" determination.

Tropical Tidbits
By Saturday morning, as the trough continues to be at its peak intensity, the surface low is projected to be moving northeast and strengthening below the 1000-millibar level. As such, the deformation zone looks to be well-developed and producing heavy wintry precipitation from Kentucky through Ohio, much of New York, and slivers of Pennsylvania, Vermont and New Hampshire. As the graphic shows, a region of significant sleet and/or freezing rain is being outlined in eastern Ohio, northwest Pennsylvania and western New York at this time. I personally see freezing rain and, to a lesser degree, sleet as precipitation types that can only be accurately predicted immediately prior (i.e. 24 hours or less) to the event, simply because more factors are involved in getting freezing rain relative to the factors involved in producing snow or rain. So, while I will refrain from calling for a significant ice event from this storm, I certainly recognize the possibility of such an outcome, and model guidance on ice accretion will be analyzed further shortly.

Tropical Tidbits
By Saturday morning, the surface low is forecast to have strengthened further, with the deformation zone now in place from the northern Ohio Valley along the Great Lakes into extreme southeast Canada. Again, the GFS here anticipates a not-insignificant region of freezing rain and/or sleet, particularly from New York through northern Vermont and New Hampshire, as well as a good section of Maine.

In terms of accumulations, everything but the kitchen sink looks to fall from this storm.
Pivotal Weather
The heaviest accumulating snow is expected to fall from Kentucky into Ohio, with the highest totals projected in southern Canada along the Great Lakes. As is generally the case with dynamic winter storm forecasts more than 48 hours out, snow accumulation forecasts are rife with caveats. While it is wise not to see these numbers as written in stone, it is also wise to believe that this storm has the potential to produce significant snow totals in excess of 12". Exact amounts and the location of relative maxima in amounts will change as we get closer to the event, but it is quite apparent that this storm has the ability to lay down a swath of over 12" of snow across a sizable section of the Ohio Valley.

Pivotal Weather
I show this image of forecasted freezing rain accumulations as a word of caution more than anything. First, notice how jagged and strange the placement of these accumulations are, almost like a contorted snake. This is a symptom of the GFS being unable to resolve the environment to a fine enough degree - whereas the NAM model has far higher resolution (that's why NAM hi-res graphics look so pretty), the GFS and other global models have lower resolution, simply because they forecast for the entire world, as opposed to the NAM, which forecasts for the United States. If the GFS model was made to create global forecasts at the NAM's resolution out to 384 hours, the forecast run could take hours to complete! So, let's take a look now at the NAM's forecast for freezing rain accumulations.
Be warned, the NAM does not yet have the full timeframe of this storm in its sights yet, so ice accumulations will seem far lower than they may actually turn out to be.

Pivotal Weather
Now that's a lot easier on the eyes, isn't it? The NAM's ice accumulation forecast has a swath of freezing rain that looks far smoother, far less jagged and contorted than the GFS' image. Again, however, I post this partially as a word of caution. The NAM is notorious during the winter season for amplifying wintry precipitation accumulations beyond what they end up being. For example, in previous seasons it hasn't been uncommon for the NAM to project 8" of snow in one area while the GFS and ECMWF support up to 4" at best. This applies to freezing rain as well, and I believe that while the NAM is almost certainly over-doing ice accumulations here, it gives a good idea of where freezing rain *could* accumulate when this storm begins. Areas from northern Mississippi and eastern Arkansas through western Tennessee, western Kentucky, Indiana and Ohio could all be at risk for some ice from this storm. I'm a bit skeptical of the projected freezing rain in Louisiana, but with a storm system this dynamic it certainly bears watching.

To Summarize:

- A potentially significant winter storm is expected to impact the Ohio Valley and Northeast in the January 12-14 timeframe.
- While these regions will initially experience rain, a heavy snow event is expected for portions of Kentucky, Indiana, Ohio, and Canadian areas near the Great Lakes.
- Given the dynamic nature of this storm and the body of warm air affecting a region that only recently escaped from a "deep freeze", accumulating freezing rain is possible, particularly in a zone from western Tennessee/Kentucky and eastern Arkansas into Indiana, Ohio, and northern portions of Pennsylvania, New York, Vermont, New Hampshire and much, of Maine.
- While amounts will be refined in coming model runs, snow accumulations in excess of 12" are possible, particularly in Ohio and southern Canada.
- While amounts will likely be determined only shortly prior to the event, ice accumulations in excess of 0.25" are possible, particularly in Ohio, northern Pennsylvania, New York, Vermont, New Hampshire, and Maine.


1 comment:

Anonymous said...

andrew, thanking you for sharing your forecasting talent and skill
with "we the peeps" !!! your timely warnings are really appreciated...
gives all of us in the impact zone more than adequate warning