After several days of ups and downs, we’re gaining clarity on the weekend storm.
Forecast models continue to suggest the center of the storm will track to west and north of Washington, meaning the capital will be on the warm side, where winds from the south funnel in humid, subtropical air and temperatures are too high for wintry precipitation to last long. After more than an inch of rain, gusty winds from the north will drive in bitterly cold air, sending temperatures off a cliff into the single digits, with subzero wind chills.
It’s going to be a wild weekend, and we see it going something like this:
Precipitation begins Saturday afternoon as rain and wintry mix — more wintry mix in the north and west suburbs, more rain east of Interstate 95. Precipitation in the immediate metro should change over to all rain Saturday night, and it could be heavy at times. In the colder suburbs, it could take longer for the wintry mix to change to rain.
The storm eases up Sunday morning, and temperatures begin to drop, enough so that there’s a very slight chance for snow as the storm ends, not enough for significant accumulation.
Total liquid precipitation could accumulate to around 1 to 1½ inches, although totals up to 2 inches can’t be ruled out. It will be falling on top of the remaining snow, so flooding will be an issue for creeks and streams. Hydrologists at the National Weather Service have yet to issue any statements on the prospects for river flooding, but at the very least, localized flooding and ponding is likely during the storm.
The cold front will pass over Washington on Sunday, and winds pick up behind it Sunday night. Gusts in the immediate metro area could reach 40 mph. Wind gusts in the higher elevations north and west of the Beltway will be stronger and might warrant a wind advisory by the National Weather Service.
The winds are carrying cold, Arctic air down from the north, and walking outside Monday will feel like a slap in the face. Sunrise temperatures will be in the single digits in the suburbs and about 12 degrees in Washington. The wind chill will be minus-10 to minus-15 area-wide. High temperatures will be of little relief, reaching only 20 degrees.
The bitter cold continues through Tuesday, and daytime temperatures don’t climb above freezing again until Wednesday.
Even though the weekend became much more clear as of Thursday, there are still minor uncertainties. Three things we’re still considering:
Are the models accurately capturing how cold the air will be near the ground Saturday afternoon?
Temperatures will be cold near the ground because of high pressure over the Northeast and the cold-air damming phenomenon it creates, which we mentioned in Wednesday’s forecast. Winds flowing away from the high pressure push cold air into the Washington region, which is dammed up by the mountains to the west. Because of this, Washington could get sleet and freezing rain in the immediate metro area for a brief period of time as the storm begins, before warm air from the south takes over and forces the precipitation to change to rain. How long it takes for that to happen has always been difficult to predict, and models rarely get it right.
Could rain change to snow as the storm ends on Sunday?
As of Thursday, the models seemed to rule out the possibility of a changeover to snow, but we’re unwilling to ignore it altogether, so we’re tabling it for now.
Snow showers are possible Sunday night and Monday
Whether the models say so or not, snow is possible Sunday night and Monday. A ton of very cold air will be pouring in from the northwest at high levels of the atmosphere, which can act to destabilize things and generate clouds and precipitation. It happens frequently after big nor’easters — a stream of very localized snow showers will develop somewhere in the region. If it’s heavy enough, it can even lead to accumulation, reduced visibility and travel issues. This isn’t a guarantee but something we’ll be watching for after the front passes.