The Washington PostDemocracy Dies in Darkness

Washington receives first measurable snow in 372 days, with another threat looming Sunday

A coating of snow and sleet covers the ground in Logan Circle in the District on Tuesday morning. (Joe Flood/Flickr)

Washington was officially coated by 0.3 inches of snow and sleet Monday night, ending its third-longest streak on record without measurable amounts. More wintry precipitation could fall in the region Sunday into early next week as another storm approaches.

The 0.3 inches of slop at Reagan National Airport, the official observing site for Washington, was not enough to put an end to the District’s longest period on record without receiving at least a half-inch of snow, which stands at 705 days and counting.

Monday night’s wintry mix generally produced a coating to an inch of snow and sleet from the District northward. Most of the precipitation fell between about and 6 and 9 p.m., after which the precipitation tapered off to light freezing rain and drizzle, offering a glaze of ice (between 0.05 and 0.15 inches) north and west of the Beltway.

The amount of snow and sleet that fell inside the Beltway, around a coating, was consistent with Capital Weather Gang’s low-end forecast for the area. To the north, amounts between 0.5 and 1.0 inches were a bit below the predicted 1 to 3 inches.

Rain, which moved into the region around sunset, changed to a wintry mix as predicted, but the intensity and overall amounts were somewhat less than models indicated.

The wintry mix slicked untreated roads and sidewalks, but treated and well-traveled roads mostly remained wet.

Sunday-Monday storm potential

Computer models are advertising the potential for the next bout of wintry weather Sunday into early next week. Depending on which model you believe, it could be a minor event or perhaps something more significant.

Interestingly, the responsible storm is the same one predicted to bring blizzard conditions to the Sierra Nevada in California on Wednesday and Thursday.

Atmospheric river in California poses debris-flow threat from wildfire scars

The American modeling system leans more toward a minor event, whereas the UKMet, Canadian and European models suggest a moderate to major winter storm.

These international models track the storm far enough south to pose a snow threat in the region. They forecast a zone of low pressure ejecting from the Southwest United States to end up between Kentucky and Ohio late Sunday before a new low-pressure center forms over eastern North Carolina. That secondary low will help hold the cold air in across our area, yielding a mostly snow scenario.

However, even if the secondary low forms to our south along or near the coast, how quickly it develops and exactly where it tracks would determine how much snow we see. Anytime the primary low tracks as far north as Kentucky or Indiana, we have a steep hill to climb to garner significant snowfall. Lots of pieces have to come together.

The European model Tuesday showed a rather extreme forecast, with an intense secondary low-pressure zone developing in eastern North Carolina on Sunday night before stalling near the Virginia Tidewater on Monday, and then crawling up the coast of the Delmarva Peninsula through Tuesday, just offshore. Its solution produces tremendous and historic snowfall in the Mid-Atlantic. However, with the storm five to seven days away, such a forecast must be considered with skepticism.

The European model ensemble, a set of 50 simulations with slight tweaks to each one to capture uncertainty, is not quite as extreme as its main simulation about the snow potential. If you take the average of the simulations, it indicates about one-third the amount of snow as the main simulation, but that’s still not insignificant (around 8 to 10 inches).

The latest American model forecast doesn’t show the necessary ingredients for a major snow event. It tracks the low-pressure zone to our northwest, which usually is not favorable for snow as it draws mild air into our region. That said, the model still predicts some snow in the storm’s initial phase early Sunday before the cold air is scoured out and precipitation changes to a wintry mix and rain, not unlike the storm system Monday night.

The key differences in the model forecasts are apparent in their ensemble systems, which illustrate the range of storm track possibilities. As shown in the image below, the American modeling system simulates more northerly storm tracks, less favorable for snow, compared with the European modeling system.

Recall that the American model struggled in its prediction for Thursday’s weather, at first calling for a major snowstorm, whereas the European model correctly called for the storm to miss to our south. Snow lovers might hope that the European once again carries the day.

At this point, it’s too early to determine which model will win out. We’ll be monitoring the potential storm over the next couple of days while waiting for the models to converge on a solution.