Tuesday, January 19, 2016

January 22-25 Potentially Historic Winter Storm

A potentially historic winter storm looks to be unfolding for portions of the Eastern U.S.

Tropical Tidbits
A low pressure system is forecasted to develop in the South US and push northeastward to the area just offshore the Mid-Atlantic, with this coastal storm fully unfolding around January 23rd-24th. The above image shows the GFS 500mb geopotential height contours and mean sea level pressure values for the morning of January 24th. We see the snowstorm located fairly out to sea, at approximately 985 millibars. This track would produce the snow map below, taking this solution verbatim.

Tropical Tidbits
This solution would bring about 6-12" of snow to the Kentucky and Tennessee region, extending into extreme southern Indiana and a good chunk of southern Ohio. We also see similar amounts into northern Arkansas and southern Missouri, as well as North Carolina. Amounts on the order of 12-24" are outlooked for West Virginia, particularly the southern part of the state, into the majority of central Virginia, New Jersey, and eastern Pennsylvania into southern New York, with some slightly lower amounts further east into Massachusetts. Long Island is also forecasted to receive upwards of 12" if this solution were to verify.

Tropical Tidbits
To emphasize how critical the placement of this system will be, take a look at the ECMWF model's 500mb geopotential heights and mean sea level pressure values for the morning of January 24th, the same timeframe as the GFS graphic. We see the system at 984 millibars, pretty similar to the GFS, but the system is clearly displaced further west. Given how anomalously warm the Atlantic currently is, this shift could easily push those two to three feet amounts inland, and leave the coastline with rainy conditions. This run of the ECMWF has snowfall amounts of over 30" in central Virginia, but lesser accumulations the further north and east you go.

Tropical Tidbits
The GEM model shows amounts in the 6-12 inch range for most of Missouri into the southern parts of Illinois, Indiana and Ohio, as well as much of Kentucky and northern Tennessee into western North Carolina. Amounts in excess of 30" are forecasted from Maryland into Pennsylvania, certainly an incredible amount of snow, but not entirely off the table given how strong and persistent this system may end up being. Again, the placement of this storm will be critical to who gets the heaviest accumulations, and we likely won't know who will receive this jackpot until the storm is actually happening.

Tropical Tidbits
One last bit of advice, do not bite on any particular model run for this storm. The strength of this storm, as well as how long-lasting it will be, among other factors, makes me way too uneasy to trust any single solution, hence why I presented a plethora of models here. The above graphic shows GFS ensemble spread in MSLP values for this storm. The warmer colors to the left and right of the system indicate increased uncertainty with where the storm will track. Again, this emphasizes how no single solution is set in stone, and thus should not be taken at face value. A lot of change will happen in the next several model cycles, and the heaviest amounts could plausibly shift a substantial bit as these changes unfold.

To summarize:

- A potentially historic snowstorm is forecasted to occur along the East Coast over the January 22-25 period.
- Currently, the Maryland/Virginia/Pennsylvania region is on track to receive the heaviest amounts.
- The heaviest accumulations could reach or exceed 30".
- Enough uncertainty still exists to change the storm track substantially, as well as shift the heavy snow axis and amounts.