Confidence increasing in a major storm, but where?

Good afternoon.

It is a busy day for all weather centers in the east, as we monitor all the weather models for any potential trends on what might be a very significant winter storm for many areas along the east coast starting Friday. However, there remains uncertainty, which makes placing forecast totals and specific impacts for individual areas a fool’s exercise, even though some models show very impressive – and potentially historic – totals for at least some areas. Hence, our confidence is much higher today that SOMEONE will see a severe to extreme winter storm, but for many areas it is still uncertain in whether or not they will be included.

It is also important to note that the upper-level energy that will be associated with the coming storm remains over the northeastern Pacific, and will make landfall later today or very early tomorrow in the Pacific Northwest. That region is very poorly sampled in terms of weather observations, and hence our confidence isn’t as high as it could be. Once it makes landfall and we get good observations from weather balloons along the west coast (the 00Z models might ingest them and the 12Z models tomorrow should have them all), we should have a much better idea. Perhaps tomorrow we may be able to pinpoint things enough to forecast for specific areas.

Upper level (500mb) energy and vorticity as of the afternoon of January 19. The energy likely to be involved in the storm is just off the Pacific Northwest.

Upper level (500mb) energy and vorticity as of the afternoon of January 19. The energy likely to be involved in the storm is just off the Pacific Northwest.

The overall synopsis remains largely the same, as it is likely a strong low pressure area will form over the southeastern US and rapidly intensify as it pushes over the eastern US and offshore. The placement of the low center is very important in determining precipitation type for marginal areas and where the heaviest snow will be, along with wind impacts. There remain several scenarios, but we are starting to hone in now. Regardless, there are dramatic differences in impacts that could be felt.

Scenario 1: Low exits far south and remains there (15% chance)
12Z GFS (January 19) ensemble run for early Saturday morning. Notice some members take the storm well south.

12Z GFS (January 19) ensemble run for early Saturday morning. Notice some members take the storm well south.

Although none of the operational models show this possibility, some ensembles, including of the GFS and CMC, are showing a very southerly track. That would largely spare most of our region, except for the southern Mid-Atlantic, of the heaviest impact snow. The greatest impact would likely be confined to areas from Virginia southward, although the impacts in those areas would likely be severe. For the rest of us, light snow and very cold weather would dominate. This is slightly more plausible IMO than yesterday due to the southerly trend in ensembles.

Scenario 2: Low exits in North Carolina/southeast Virginia, remains south of benchmark (50% chance)
12Z GFS (January 19) run for Saturday afternoon. This is a blockbuster storm especially for the mid-Atlantic who get multiple rounds of heavy snow.

12Z GFS (January 19) run for Saturday afternoon. This is a blockbuster storm especially for the mid-Atlantic who get multiple rounds of heavy snow.

Right now, this is becoming the most likely scenario, supported by the GFS and operational ECMWF. In this situation, the low pressure area rapidly intensifies near Cape Hatteras or slightly north (up to the mouth of the Chesapeake Bay) and continues on an east-northeast trajectory out to sea. This would focus the heaviest impacts in a corridor through the central and northern mid-Atlantic, including the DC and Baltimore areas and up to Philadelphia into southern Pennsylvania and southern New Jersey.

Those areas could potentially face a very crippling event with very high snow totals in at least some areas, shutdowns to commerce and grounding of virtually all travel. High winds and coastal flooding would also be possible for some areas, particularly in the mid-Atlantic coastal regions. New York City would likely be on or near the edge of the severe impacts, with parts of southernmost new England also in that position. Impacts would drop rapidly northward.

Scenario 3: Low exits in central mid-Atlantic, tracks offshore near/north of benchmark (30% chance)
12Z CMC (January 19) model run for Saturday morning. Notice the rain-snow line along the coast and pushing inland. It doesn't get too far.

12Z CMC (January 19) model run for Saturday morning. Notice the rain-snow line along the coast and pushing inland. It doesn’t get too far.

A somewhat less likely scenario also exists in which the low tracks farther north, which is supported by the CMC model and many of its ensembles. In this scenario, the low tracks across Virginia and emerges in the Delmarva or southern New Jersey, tracking east-northeast over or north of the 40/70 benchmark. This would be a massive event for the interior mid-Atlantic, especially southwestern Pennsylvania, western Maryland, eastern West Virginia and far northern Virginia, and would also result in potentially crippling impacts beginning just north and west of the I-95 corridor from the central Appalachians to interior southern New England.

In the urban corridor, however, precipitation type would be an issue, especially near the coast in areas such as Cape Cod, eastern and southern Long Island and the Jersey Shore. Since warm air may try to enter the region and temperatures may rise a few degrees above freezing into the upper 30s or low 40s during the peak of the storm, precipitation may change to rain for a while (or mix with rain or sleet), which would likely reduce snow impacts. High winds and coastal flooding would still be major problems though.

Scenario 4: Some other solution (5% chance)

No models are showing any other solutions, such as a track well to the north and inland, or no storm forming at all. Some of those were mentioned yesterday but don’t appear very likely anymore. Impacts from these alternate scenarios would vary widely, from little or no problems, to an eastern/southern New England focus if the low is far enough offshore, to warm air penetrating the region and confining snow to far inland. None of those scenarios have model support right now.

Conclusion

Confidence is increasing in a significant, possibly crippling, winter storm affecting at least some part of the Northeast or Mid-Atlantic starting Friday and lasting possibly until Sunday. That said, exact snow amounts are highly dependent on mesoscale factors and vary widely, which cannot be forecast this far out, even though some models have shown absolutely ridiculous snow totals (which I will not mention here). After all, we don’t even know who is getting what right now, although early indications have the inland mid-Atlantic (i.e. west of I-95 from central Virginia to southern Pennsylvania) at greatest risk of very severe impacts. As there is plenty of backing cold air available, precipitation type issues should largely be limited to the coast, where warm maritime flows may raise surface temperature above freezing if warm air can push in.

It is too early to panic and get crazy about this storm. However, it certainly does not hurt to make initial preparations, as the sooner you are prepared, the sooner you are ready when it actually does come – if it does. Even if it does not hit you, the supplies are useful for the next time.

Forecaster Craig Ceecee (@Ceecee_Wx)

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