Keep Calm and Carry On: weekend storm update

Good afternoon.

Given the active pattern and storm potential, until we know more, I will try to at least write a forecast every day this week. There is a lot of talk on social media right now, but not a lot of agreement. It is likely that, if this storm impacts the east coast, it will be in the Friday to Sunday timeframe. A post from Pittsburgh meteorologist Kristin Emery explains the situation well, and I am currently in total agreement.

Models all over for weekend storm. Snow could be little or huge depending on https://t.co/PHMr2Idz7I for updates. Keep calm and carry on.

Posted by Kristin Emery on Monday, January 18, 2016

It is likely that a storm will form SOMEWHERE, either on the coast or offshore, but the placement will have dramatic differences in impacts. For this post, I am mentioning several possible scenarios which I will explain in depth. Snow amounts, wind and coastal storm surges cannot be forecast this far out, it is best to ignore any such maps at this stage. After all, we don’t even know where this is going.

Scenario 1: Low exits far south and remains there (10% chance)

This is not really supported by any models other than a very small number of ensembles, particularly CMC ensembles. However, I believe it is still a viable scenario if the ridge can dig southward. In this case, there would be relatively little impact to our regions, as most of the precipitation and wind remains well south. It would be cold though!

Scenario 2: Low exits in Carolinas and then well offshore south of benchmark (30% chance)
12Z GFS ensemble member positions for Saturday afternoon (from January 18). Notice most members south of the operational.

12Z GFS ensemble member positions for Saturday afternoon (from January 18). Notice most members south of the operational.

This is supported by the ECMWF model and the GFS ensembles. The European model has had mixed results lately – it famously flopped on the blizzard last January, but also famously nailed Hurricane Joaquin. I have to put a little more weight in this forecast as a result. Given that the storm would miss the benchmark, the heaviest impact would be concentrated in the Mid-Atlantic and near coastal areas, with much less impact farther north (including in most of New England). As cold air would be rushing down, precipitation type would largely not be a factor here. However, the impact would focus farther south.

Scenario 3: Low exits in lower Mid-Atlantic, tracks just offshore near benchmark (25% chance)
12Z GFS run for Saturday afternoon (from January 18). This is a real snow maker for the entire I-95 corridor, but caution is necessary this far out.

12Z GFS run for Saturday afternoon (from January 18). This is a real snow maker for the entire I-95 corridor, but caution is necessary this far out.

Much of the hype is on this forecast run, which is shown in the 12Z GFS and other recent GFS runs. It is a reliable model, but there are many models showing other runs as well resulting in very little consistency. With cold air rushing down from Canada into the eastern US, it is likely that if this verifies, heavy snow and blizzard conditions would occur along nearly the entire east coast, with only headland areas like Montauk Point and outer Cape Cod/Nantucket experiencing mixing or rain. This would be essentially a 1996 redux. HOWEVER, I only give it a 25% chance of such happening at this time, given the enormous model spread.

Scenario 4: Low exits in upper Mid-Atlantic, tracks just off southern New England coast (20% chance)
12Z CMC run for Saturday morning (from January 18). Classic I-95 dividing line event.

12Z CMC run for Saturday morning (from January 18). Classic I-95 dividing line event.

The CMC has not budged either, with the 12Z run showing this situation. This would be a classic I-95 dividing line event, with rain on the coast changing to snow (or sleet) farther inland, along with high winds and coastal flooding. Snow there would be limited to the backside after the cold front passage. The cold air rushing south would allow for snow inland and impressive accumulations, but would not be able to penetrate to the warm air at the coastline. If cold air CAN penetrate low but is overcome by warm air aloft, some areas may even experience an ice storm, particularly in interior valleys. The CMC is not a particularly reliable model, so I believe this is somewhat less likely.

Scenario 5: Other possibilities (15% chance)

Those are not exhaustive possibilities, and something not modeled could still occur. That includes an inland low holding all the energy and pushing warm air inland, a cold air wedge scenario that results in a primarily freezing rain/ice storm event or no storm at all forming, resulting in standard winter conditions.

Conclusion

We are 4 to 6 days away from any potential storm. At this time, typically track forecasts are more useful than specifics and this is no exception. Uncertainty is still far too great to pinpoint any particular snow forecast (not until midweek at least might we be able to) and so many possibilities exist. Stick to trusted sources like NWS and reliable media outlets, and remember to keep a close eye on the forecast but avoid hype. Not worth it right now.

Once again, keep calm and carry on (as Kristin Emery said).

Forecaster Craig Ceecee (@Ceecee_Wx)

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