March 5, 2021

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After Saturday’s ice, more winter storms line up for D.C. area – The Washington Post

3 min read

This is the same storm that may bring snow and ice as far south as Austin and Houston, but because it is slated to pass to our west as it moves along the zone of greatest temperature contrasts, it will draw mild air into the region. Washington sits at the eastern fringe of a sprawling and potent Arctic air mass, putting us in a stormy, but relatively mild, zone.

This next weather system will quickly exit Tuesday morning, when afternoon temperatures may rise into the 40s.

Then eyes turn to the next storm, on Thursday, which has more potential to offer frozen precipitation before a possible changeover to rain during the second half of the day.

Thursday wintry mix potential

Colder air will filter back into the Washington region by Wednesday in the wake of Tuesday’s storm, with highs in the 30s.

By early Thursday, a strong Arctic high-pressure system will be located over southern Canada in a favorable position to supply cold air east of the mountains. At the same time, a storm system in the Gulf of Mexico will head toward the Mid-Atlantic from the southwest.

The southwestern flow aloft ahead of that storm will be lifted over the cold dome east of the mountains, resulting in another round of wintry weather.

Computer models project that the storm will initially track to our west before reforming along the coast, arguing for a wintry mess. The scenario favors snow developing early Thursday before transitioning to ice and then rain later in the day, especially along and east of Interstate 95.

In colder areas to the west, precipitation could remain in the frozen form for the duration of the storm, with significant snow and icing. However, model projections could shift toward rainier, icier or snowier scenarios as the event draws closer. (Several weather events this winter have brought significant model shifts before storm onset.)

Most of the models are forecasting that temperatures will be in the 20s to around 30 when precipitation begins early Thursday morning, so slick conditions could develop on untreated streets and walkways. By Thursday afternoon, simulations warm temperatures into the low 30s, possibly cresting near freezing along and east of I-95.

How long frozen precipitation and freezing temperatures last will depend on how quickly the precipitation arrives and how quickly the coastal storm forms. The European and American (GFS) models differ on these details.

Many simulations in the European modeling system track the storm to our south and east and, therefore, hold on to the cold air longer, while American model simulations tend to track the storm to our west before a slower redevelopment to the east. The American model storm evolution puts us on its warm side, which allows the Arctic air mass east of the mountains to moderate more quickly, arguing for mixed precipitation that changes to rain.

The weather pattern the past two weeks has been unusually hard to predict, because the D.C. area has tiptoed on the edge of the Arctic air mass invading the middle of the nation. This may well again be the case with Thursday’s storm, meaning it could take until Tuesday or Wednesday to nail down this forecast.

How much ice fell Saturday

According to reports from the National Weather Service, about 0.1 to 0.3 inches of ice accumulated across the Washington region Saturday, with the highest amounts concentrating along and east of I-95. This was generally in line with the Capital Weather Gang’s forecast.

Bear in mind, ice amounts are difficult to measure, and not as many observers submitted reports as they typically do for snow. Reports were spotty southeast of Washington into southern Maryland, where we imagine amounts were on the high end.

In any event, the combination of temperatures from 27 to 30 degrees and a steady dose of freezing rain and sleet resulted in one of the more significant ice events in the region since Feb. 14, 2007. The Weather Service’s issuance of an ice storm warning was the first in the District since 2008.

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