WASHINGTON - The D.C. region is getting set for another possible round of wintry weather as we head into the middle of the workweek. Similar in nature to the event seen around the area on Super Bowl Sunday, the main threats with the upcoming storm are sleet and freezing rain as opposed to any snowfall accumulation. Any frozen precipitation around the region should transition to rain by late Wednesday morning near the Interstate 95 corridor and by early afternoon for areas far to the northwest of town.
Temperatures play a key role in all of this. On Tuesday afternoon, temperatures are expected to approach the seasonal norms in the mid-40s around the region with limited sunshine. Areas north and west of the District will stay cooler, but should still make it above freezing with some limited sunshine. An area of high pressure will pass to our north during late Tuesday evening and overnight hours, eventually turning our winds out of southeast as it lifts through New England. It is this easterly component to the wind that can “trap” cold air near the surface against the mountains to our west, a process known as “cold air damming” because of how the mountains act like dam holding back water.
On Tuesday morning, the National Weather Service issued a Winter Weather Advisory, which will go into effect at 3 a.m. Wednesday and remain until 1 p.m. For areas north and west of town up towards the Maryland and West Virginia Panhandles, a Winter Storm Warning has been issued from 3 a.m. until 4 p.m. Wednesday.
The primary reason that the advisory was put in place for the immediate D.C. and Baltimore metro region is out of concern for the timing of the event, with frozen precipitation possibly falling during the morning rush hour. For icing events in particular, conditions can deteriorate quickly. We urge morning commuters to plan ahead and take it slow if they have to hit the roadways early tomorrow morning. Even though ice on roadways is expected to be patchy, it does not take much ice at all to cause big travel problems.
Timing wise, the National Weather Service expected wintry precipitation, perhaps even starting as some wet snow, to begin for the southern I-81 corridor between 1 and 3 a.m. Wednesday. The precipitation will spread northeast from there, and is expected to reach the immediate D.C. metro region between 3 a.m. and 5 a.m. There is some weather model debate on just how far to the east moisture will extend during the morning hours, and several model do indicate the possibility that areas east of the I-95 could stay mostly dry until later in the morning. Other models are indicating the possibility of a break in the precipitation around sunrise for a few hours, before moving back in during the morning hours. If either of these scenarios is true, it would help keep roadway conditions more stable around our area. Confidence is highest that areas west of Interstate 95 will be dealing with frozen precipitation during the pre-dawn hours of Wednesday morning.
Unlike the event on Sunday, where the center of the storm passed east of the Appalachian Mountains and many areas struggled to get their temperatures much above freezing the afternoon, confidence is higher with tomorrow’s event that the center of the storm will pass farther to the west. This has the effect of pulling in warmer air and should help the Interstate 95 corridor to transition over to all rain by the lunchtime hours. The mix will linger longer into the afternoon for areas north and west, but temperatures in these areas should rise above freezing as well and rain should take over prior to the evening commute.
A final concern comes following the event Wednesday night. As the storm continues to lift northward, winds across the region will reverse, turning from the south to out of the northwest Wednesday night. This will allow cold air bottled up to the north to spill back into our region Wednesday night into the early morning hours of Thursday. While it’s a rain event here Wednesday afternoon, the rain that does fall will likely wash away any road treatment chemicals from the morning hours. Temperatures quickly falling below freezing tomorrow night could freeze any wet areas that remain, which could lead to some issues for Thursday’s commute as well even though sky conditions will be dry.
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