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Snow Threat: Jan 26-27 (final call)

My idea of a higher snowfall band has come to fruition on the models, though not at quite the angle (or with the somewhat lower snow amounts) that I expected. After some considerable brain-wracking, this is what I’ve come up with:

The map calls for a somewhat more northerly solution than what is currently shown on the models, with some heavy influence from the GFS/ECMWF solutions. This season’s trend of fully developing the coastal low and SN/+SN zone slower than expected has led me to think that the greatest snowfall totals in the coastal area will be further north and east than the 12z NAM shows. This area will also likely have better snowfall ratios than areas to the south, which will help towards breaking into the 8-12″ totals.

Along the mountains, there is the potential for some good upslope along the eastern Apps in northern VA. The position may end up being off, but I’m fairly sure some part of the eastern slopes will get into the higher totals of 8-12″ as the onshore mid-level flow of moisture starts to push into the area and is aided by higher snowfall ratios.

EDIT to add that thundersnow is possible along the I-95 corridor!

Snow Threat: Jan 26-27 (first call)

Before I begin, I’d like to state that this forecast has fairly low confidence as we sit in the 3-4 day window with the coming coastal storm. There is still a lot of room for changes to the storm track and snow totals, so this forecast is to be taken with a grain of salt.

With a whole mess of rain and wintry weather from a wet inland solution via the 12z ECMWF, a rain/snow mix and precipitation cut-off closer to the coast on the 12z NAM, and a mostly out to sea but snowy coastal areas 12z GFS solution, which one are we supposed to pick? Using the last 1.5 months as a guideline of which way to lean, I have gone with what is basically the GFS solution with a more inland track and a more amplified cut-off of the eastern (above freezing) side of the storm that more closely resembles the NAM solution.

Rain and mixed precipitation is a huge concern for the coastal and southern parts of the region, which is the main reason why my confidence in this forecast is low. There is a very narrow area of opportunity for higher amounts of snowfall, and while I have more confidence that there will be a narrow strip of higher totals, where that ends up being remains a mystery.

EDIT to add that yes I do think this is a rather bullish/ambitious forecast, but it is still a first call and there’s plenty of room for change.

Snowfall Verification for Jan 20-21

I found a link on NCDC that can help me do snowfall verifications. I haven’t found an archive of the data yet, but at least I found a way to easily verify my forecasts.

Here is the 3-day snowfall total map, ending at 15z today:

Here is the comparison, using my contouring (with some smoothing to the actuals):

The mixing in the southern parts of the contours proved to be further north than I had originally anticipated, which was due to better-than-expected daytime heating and a slower development of the coastal low. The western side of the Appalachians got a bit more snowfall than I expected as lake-effect and residual moisture was able to have more of an impact.

Overall, not a bad forecast, but certainly one that needed improvements in some areas. Overall, I would give it about a C grade.

Snow Threat: Jan 20-21 (final call)

Final map… probably 90% the same, with some tweaks to the snowfall gradient in West Virginia, extent of 4-8″ in the west, small adjustment north in northern Virginia and small adjustment south along the coast.

Added a HHMM timestamp (GMT/UTC time) on the issuance time because it seemed warranted. Hopefully this is the final version for awhile, but I might consider adding one more contour for the mixing/under an inch area.


Snow Threat: Jan 20-21 (first call)

Another fun storm is upon us as we head into the end of the work week. Mixing will be a huge issue in Northern Virginia, DC and areas south. Ultimately, I expect DC to stay in snow for most of the event. While the QPF for this storm isn’t terribly impressive, higher snowfall ratios will be available further north and west, which will make areas of 4-8″ possible. The risk is mainly to the lower side along the southern edges of the contours.

Expect a final call either this evening or early tomorrow.

Historic winter storm ransacks the South… sets eyes on the Mid-Atlantic and Northeast

Areas have been blasted with up to a foot of snow from the ArkLaTex region through NC as far south as central AL/GA. This epic winter storm will continue to wreak havoc as it develops in the Atlantic and hits NJ/NYC/New England with heavy snows. Most of VA/MD likely spared the worst of the storm’s power (1-4″ of snow in most areas) as the complex system evolves.

Here is a map posted by Al Roker showing the snowfall totals as of ~7am this morning:

This does not include this morning’s totals in GA/NC/SC, of which parts of southeastern NC has seen over half a foot of snow already! I, as well as almost everyone who forecast this storm, did not anticipate how far south the snow line was going to form, which is resulting in a lot of busted calls from northern LA to central AL/GA and up through eastern NC, which called for mostly mixed precip. and rain. NC and southeast VA could still convert over to mixed precip., but not before 1-3″+ of snow has fallen in most areas.

This is already an epic storm in the south, and we still have snowfall on tap for the southern Midwest, Mid-Atlantic and Northeast, where NYC and southern New England could see over a foot of snow in spots before we say goodbye to this incredible winter storm.

UPDATE 6:00pm EST:

The 1-3″ call for NE NC and SE VA could be in question as the dry air over the region eats away at the possible snowfall and the mixed precip. zone creeps closer and closer. Still a chance for more snow to fall AFTER mixed precip. and/or rain works into the area, but hitting the top-end estimate of 2-3″ appears doubtful at this point.

Snow Threat: Jan 10-12 (final call)

This is going to be a very complicated event, with two low pressure centers interacting from the Midwest and Southeast up through the northern Mid-Atlantic as the coastal low takes over for New England. Mixing will be a problem for North Carolina, southeastern Virginia and southern Delmarva, which could shift a bit north or south, depending on when, where and how quickly the coastal low can develop. A quicker low development off the East Coast would draw cooler air down from the north and create more snow over the “Mixing” area highlighted on the map.

Snow totals have been bumped up for West Virginia and Pennsylvania as the low pressure center over the Midwest will be stronger than originally anticipated, which will help squeeze out more moisture in the western and northern parts of the region. This stronger Midwestern low is also what caused the mixing issues in North Carolina to jump northward, as it will create a stronger southerly flow in that area and will draw warmer mid-level and low-level air northward before the coastal low gets cranking.

As the coastal low comes in stronger than expected, higher snowfall totals are possible in the New Jersey, NYC and Southern New England areas as it progresses northeastward. NJ/NYC/SNE could see another round of 12-18+ inches of snow from this storm.