(Premium) Will There Be An East Coast Snowstorm March 4th-5th?

After the midweek storm which is likely to be all rain, we are watching for the potential for storm system to develop near the Southeast US in the March 3-5 period.

Strong high pressure with much colder air will follow behind the midweek storm. Meanwhile, a shortwave will dig downstream off the West Coast ridge over the Rockies. This shortwave will become part of the southern stream and cause a low pressure storm system to develop over the Central or Southern Plains. Models indicate this storm will track towards Southeast or Lower Mid-Atlantic coast by Friday.

It is still highly uncertain if this storm system will impact the our region. The models have differences in the timing and strength in the northern stream and southern stream shortwave energy, which results in great differences in their interaction — and even discrepancies in whether they interact at all. Today’s 12z GFS model keeps the storm over the Southeast and Lower Mid-Atlantic regions, as a stronger polar vortex keeps the southern stream energy farther south. The 12z GFS ensembles are mostly in agreement with this scenario.

The 12z GFS ensemble members for March 4-5th storm. The operation run on the top left corner. Only 2 out 11 members show any precipitation in our region. Image credit: PSU Ewall

The 12z ECMWF has a storm impacting our region. The polar vortex begins to retrograde out of Southeast Canada. This southern stream shortwave becomes embedded inside of a longwave trough and begins to amplify. As the surface low reorganizes off the Virgina coast, some light overrunning snow falls over large parts of the Mid-Atlantic and Northeast regions.

The 12z Euro showing the low near North Carolina Coast, producing overrungin precipatation.

The 12z ECMWF model showing the low near North Carolina Coast, producing overrunning precipitation. Image credit: PSU Ewall

The storm tracks more seaward from there and intensifies well offshore. The northern stream energy coming down the Northern Rockes and Northern Plains, catches up with the southern stream, which phases into a closed 500mb occurs in the Atlantic. This happens to late for Northeast and Mid-Atlantic to get a major snowstorm, except for Eastern Long Island and Southeast New England. A slightly earlier phase would have resulted in a major snowstorm for the I-95 corridor.

The ECMWF model with strong low well offshore.

The ECMWF model with closed 500mb and surface low March 5th a few hundred miles east of Long Island. Image credit: PSU Ewall

Today’s 12z European Ensembles were generally pretty robust with the storm system. Although the mean of its solutions was still a tad offshore (showed light to moderate snow for us), there were plenty of members that were closer the coast and showed large snowstorms — certainly a red flag. While there have been a few times this winter season where the European Ensembles were too amplified with storm systems, the trend lately has actually been for them (and other guidance) to not catch up on westward trends soon enough.

There are a few factors that could this cause this storm miss our area. If the polar vortex is too strong, this will lead to a compressed height field over the Eastern US. The southern stream shortwave energy would be sheared out or more suppressed. Also, the flow may be too progressive. While there are higher heights building into Greenland/Davis Strait, this is just happening just as the system reaches the east coast — usually you want the blocking pattern to have already been established for bigger snowstorms. Additionally, more Pacific energy coming into the Western US would flatten the Western US ridge, and thus could cause more de-amplfication of the southern stream shortwave as it tracks east, and thus a more progressive solution. Several model solutions have already suggested these disturbances flattening the ridge, and this would be consistent with strong El Nino tendencies to have an active wave-train in the Pacific.

On the other hand, we have seen a shorter-term trend with some of our storm systems this winter to come further northwest, due to strong ridging in the Western Atlantic, as well as the tighter wavelengths in general this time of year — a tighter trough would cause the storm to turn up the coast earlier. Additionally, while the higher heights are building into Greenland a bit later than most large snowstorm cases, it still is a somewhat legitimate -NAO, which still helps for snow more than it hurts. So this storm will need to be carefully monitored over the next few days.

This post was written and edited by Miguel Pierre and Doug Simonian 

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