Livin On The Edge of a Glorious Snowstorm

Hello everyone!

We’re about 8-12 hours away from the onset of snow here in the area which means it’s time for one last crack at this forecast before we sit back and see what happens.

On a large-scale, the forecast outlined this time yesterday is more or less on track.

via COD NEXLAB

The swirl we were tracking across TX/OK yesterday is now moving northeast through TN/KY and moisture is streaming north out ahead of it. Meanwhile, our Arctic airmass is well-entrenched and saves us the hassle of worrying about a rain/snow line. The problem is that said airmass might be a little too entrenched and it’s as dry as it is cold. Therefore, snow is going to struggle to make it to the ground over most of the area tonight and perhaps for much of tomorrow too.

Here’s a look at regional radar imagery and surface precipitation observations as of 4 PM. Snow is falling west and south of NYC with some rain/ice mixing in east of I-95 south of Philly. Farther north, low-level dry air is preventing snow aloft from making it to the ground.

The big question is just how stubborn that dry air is going to be over the next 24 hours.

via Levi Cowan/Tropical Tidbits

The trend in high-resolution weather model guidance over the past day or so has been towards that dry air being more stubborn than originally forecast. This is supported by surface observations today showing the area of high pressure over Quebec a bit stronger than expected. It also fits a bit better with what’s historically expected from a setup like this. Remember in yesterday’s forecast we talked a bit about how the fact that this storm was weakening and not strengthening as it approached the region gave some pause about the higher-end snow forecasts. Sure enough, it appears that skepticism was warranted.

With all this in mind, here’s one last crack at a snowfall accumulation map for the area.

I’m still quite confident that the heavier bands will be able to work their way into southern NH and York County ME. That’s where the jackpot will be for this storm and over a foot is likely here. The mountains seem likely to miss out almost entirely which is a real bummer for those of us hoping to ski some fluffy snow this weekend. The forecast challenge is really figuring out points in between. I suspect the real gradient will be a lot sharper than it appears on the map here. You might only have to drive 10-20 miles to get from dustings to nearly a foot, but beyond the idea that this is most likely to happen somewhere between Fryeburg-Lewiston-Camden, there’s no way of knowing exactly which towns will fall on which side of that gradient.

Snow is still on track to start in SW NH later this evening before struggling northeast into SW Maine tomorrow morning. Snow will reach its maximum northern extent sometime midday tomorrow before departing to the east tomorrow afternoon.

Whatever snow is able to fall will not hesitate to become airborne once again as northeasterly breezes pick up and the frozen ground prevents much if any melting.

-Jack

Calm Before the Storm Today

Hello everyone!

The nor’easter discussed in great detail yesterday afternoon is still on track to arrive late tonight from southwest to northeast with moderate/heavy snow. Before the first flakes fly, we’ll enjoy quiet and cold weather today thanks to a strong area of Arctic high pressure.

A quick look at surface analysis and observation data this morning shows that big high pressure area over Quebec while our developing storm is currently split into two components over TN and off the SC coast. All the little numbers you see are temperature observations. If you haven’t yet stepped outside this morning, make sure to bundle up when you do so! Temps across the region range from around 10 below up north to around 10 above in the south.

Skies right now are mostly clear, but morning sunshine won’t last long as clouds approach from the southwest ahead of the storm. By mid-afternoon, the entire region should be seeing overcast skies.

As we move into the later afternoon hours, calm conditions will gradually give way to light northeasterly breezes as the storm’s snow shield gets closer.

While not shown on this map, I’m thinking ocean effect snow showers are possible along the NH Seacoast and adjacent parts of York County starting around 4-5 PM. We don’t quite have enough of an easterly component to the winds for much accumulation but an early dusting is possible in some spots before the primary round of snow arrives later tonight.

By 9 PM, snow should begin falling over far southwestern NH while the rest of the area remains cold and dry. Snow will slowly struggle northward overnight as low-level dry air erodes. Just how fast and far north this process can occur will determine snowfall totals especially for spots north of Brunswick-Lewiston-Fryeburg.

Here’s an updated look at what I’m thinking for snowfall totals from this system. There really haven’t been any significant changes from yesterday’s forecast, though I trimmed amounts back a smidge on the northern edge. When all is said and done, the observed snowfall map will have a really sharp gradient somewhere near where my 4-8″ swath is. Amounts north of that may struggle to reach 2-4″ while points just south could exceed 12″. Unfortunately there’s just not quite enough confidence to try and pin down that gradient location more precisely. Perhaps we’ll get some more clues with today’s model guidance and observational data. If that information indicates that noteworthy changes might be needed to this snow map, I will have another update this evening. Otherwise, we’ll go with this forecast and wait to see how it turns out.

Another aspect of the storm worth mentioning is the possibility for near-blizzard conditions as our fluffy snow is blown around by gusty northeast winds tomorrow.

This map depicts the chance that a given point will see <0.5 mile visibility with snow and winds over 30 mph. Because this product uses sustained winds instead of gusts, the highest probabilities are concentrated heavily offshore but coastal spots particularly in southeastern NH and south of Portland in Maine are likely to make a run at blizzard criteria (visibility <=0.25 miles with frequent gusts >=35mph for three or more hours) tomorrow morning. We might fall just short (hence the lack of blizzard warnings from the NWS) but the impacts will be similar regardless.

-Jack