Major Blizzard Set To Move In Tonight

Hello everyone!

We are all systems go for a major blizzard tonight and into tomorrow morning. Low pressure now forming S of Washington DC will move NE over Cape Cod and into the Gulf of Maine by early tomorrow morning. As it does this, a powerful upper level disturbance will drive explosive development of the storm, pulling it west and stalling it out for a brief time tomorrow morning over the Gulf of Maine. The storm will then slide SE offshore tomorrow during the day. Now that snow is beginning to fall over NH and SW ME, we can rely less on model guidance and more on observations to determine if we need to change the forecast at all.

1 PM Verification Of HRRR Model For Temps In PWM. Images From Weatherbell And Aviation Weather Center.
1 PM Verification Of HRRR Model For Temps In PWM. Images From Weatherbell And Aviation Weather Center.

Model guidance has pretty much locked in the amount of liquid equivalent that will fall (around an inch in the mountains and between 1.5 and 2″ along the coast) so now the snow forecast goes over to ratios. Will the snow pile up quickly with very high snow:liquid ratios or will it be sludge that hardly accumulates at all with low snow to liquid ratios? Given strong snow growth dynamics (see last night’s post), this will largely come down to surface temps. As the above image shows, temps are currently well below model forecasts across the coasts (by around 5 degrees) meaning that a drier, fluffier snow is looking likely.

WV Satellite Imagery Showing Everything Coming Together For A Major Snowstorm. Image Credit: COD
WV Satellite Imagery Showing Everything Coming Together For A Major Snowstorm. Image Credit: COD

In the upper levels, the water vapor satellite tells the story. Powerful energy is racing SE across the Great Lakes with abundant lift and moisture ahead of it. As soon as that upper level energy hits the coast, the storm will explode and snow will intensify as moisture is dawn in from the Atlantic. The upper level trough is already weakly negative and well on its way to becoming very negative as the energy works east. This is the mechanism behind the explosive strengthening of our storm.

2:15 PM Radar Showing Moderate Snow Moving In.  Image Credit: COD
2:15 PM Radar Showing Moderate Snow Moving In. Image Credit: COD

Radar this afternoon is showing bands of moderate snow working into the area from SW to NE. These will eventually overspread the entire area this evening and will continue through the overnight hours. During that time, the storm offshore will really get going and bands of snow will begin moving in off the ocean. As the storm stalls and slides out to sea, those bands will stall and then collapse SE with it. Where exactly these bands stall out tomorrow morning will determine who gets the jackpot totals. Under the heaviest bands, 30″ totals are a distinct possibility though only a few towns will see those so the general 18-24″ forecast stands.

Surface Map Showing Low Pressure Just Developing Over Virginia. Image Credit: SPC
Surface Map Showing Low Pressure Just Developing Over Virginia. Image Credit: SPC

Here’s the surface analysis from 2 PM this afternoon showing our storm beginning as a benign 1004mb low pressure system embedded within 80F temps in Virginia. From its humble origins, it will turn into an all out blizzard as it loops off the MA coast tomorrow morning. This loop/stall will be a result of the upper level low capturing the storm and pulling it west underneath the upper level low. Once the storm is “stacked” its intensification will halt as its source of energy is removed and the entire system will slide SE into the North Atlantic. This will occur midday tomorrow.

The explosively developing storm will result in very strong winds which, combined with the dry/fluffy snow will result in blizzard conditions along the coast tomorrow morning. Winds could gust to 50mph along the coast resulting in near zero visibility. For more details on the wind threat, check out last night’s post.

Updated Snowfall Forecast
Updated Snowfall Forecast

Here’s my latest snowfall forecast. I expanded the 18-24″ zone farther NW into the mountains as a very high fluff factor is forecast there and models have been hinting at a strong band setting up there. I took the coast down to a blanket 18-24″ as latest guidance has trimmed QPF back slightly though I left the potential in for up to 30/32″ in any of the heaviest bands that set up. For more on how mesoscale bands set up and why they have such an impact on snowfall, check out my post from our last major snowstorm just a few days ago!

Don’t look yet but another snowstorm is becoming more likely for Thursday. At the moment it looks like a Norlun trough type event which are notoriously hard to predict. Stay tuned for more info tomorrow and through the week!

-Jack

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