9:10 a.m. update: Snow continues to advance through the area. It has been reported in a good chunk of Loudoun and parts of Montgomery counties. The snow isn’t terribly heavy to start, and the heaviest should come later today overall, but the cold readings are going to help it be fluffy and eager to accumulate. Plan on road conditions going downhill shortly after it begins.
Here’s a look at HRRR simulated radar for noon:
— Doug Clark (@stormes44) February 21, 2015
— JB (@jbrnr) February 21, 2015
8:30 a.m. update: Snow is quickly pushing into the area, and it appears it will keep running east fairly fast. Snow should be into D.C. between 9 and 10 a.m. at this rate, probably covering the whole region by noon or so. Thanks to very cold temperatures, the first flakes stick.
Snow moving into western suburbs. Should advance east across the area fairly quick. Instant sticking once it starts. pic.twitter.com/YdPCIQ6IKM
— Capital Weather Gang (@capitalweather) February 21, 2015
8:00 a.m. update: The National Weather Service extended the winter storm warning to the east overnight. It now includes all of Loudoun, Montgomery, and Howard counties as well as counties previously under warning to the north and west. The warning area snowfall numbers start at 4-6 inches and increase to 6-8 inches at peak as seen in the NWS forecast map below. Fairly similar to ours (further down this post) in most spots.
TODAY’S DAILY DIGIT
A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.
2/10: Snow on a Saturday is nice for us weather watchers. Otherwise, winter could end and I’d be OK with it.
Today: Cloudy, snow to wintry mix. Highs: Mid-20s to near 30.
Tonight: Wintry mix. Lows: Low-to-mid 30s.
Tomorrow: AM showers? Variably cloudy, breezy. Highs: Low-to-mid 40s.
FORECAST IN DETAIL
From 5:00 a.m.: Today’s forecast is a painful one. Both as a forecaster and as anyone who has to deal with it as part of their weekend planning. The evolution is still somewhat uncertain at this short range. If we went into this storm system without the extreme cold ahead of time, it would arguably be considerably easier to figure out what was going to happen. It would probably mostly be rain. Not the case here though. Snow lovers: we might as well make something of this deep chill, right?
Today (Saturday): There may be see some early a.m. sun (or a great sunrise as clouds roll in?) to start the day. If so, thicker clouds soon follow. Snow begins to advance into the area during the morning. Maybe as early as 8 a.m. west, but becoming more likely by 10 a.m. even into D.C. Everyone should see some flakes by noon or so, and they may be increasing in intensity by then as well.
Even as snow arrives, it’s a bit tricky as to the details. One thing is certain, wherever snow falls travel is likely to deteriorate, potentially becoming treacherous, and possibly staying that way for much or all of the event. It’s also likely there will be a cutoff across the region, between decent snow accumulation and much lesser snow accumulation. The heaviest snow — it could truly be heavy at times — probably comes during the afternoon. It tries to last into the evening before sleet mixes in and takes over.
There is both upside and downside potential to our 2-5 inch forecast for much of the local area (higher N/W, lower S/E), as snow can pile up quick in bursts and bursts can be fickle. Daytime temperatures peak mainly in the mid-20s to near 30, but actual Saturday highs could occur prior to midnight in the low-to-mid 30s. Confidence: Medium
Tonight: Snow changes to sleet from south to north during the evening. Best guess for now in D.C. is that the change occurs somewhere in the 6 p.m. to 9 p.m. range, give or take. Even as this changeover occurs, temperatures should be very slow to rise, and roads are likely to be a mess across the region into the night. Ultimately, much of the area goes over to plain rain after a period of freezing rain, but it may even stay mostly frozen once you’re a bit north and west of the city.
Enough ice to cause very slippery conditions could also occur in and around D.C. before a change to rain. Temperatures either stay steady overnight or slightly rise. So, lows are pretty similar to late-night readings in the near 30 to mid-30s range. Confidence: Medium
For related traffic news, check out Dr. Gridlock. Keep reading for the forecast through the weekend…
Tomorrow (Sunday): If you’re looking for a break from the extreme cold, this is your day! The storm system moves away, although a few showers may persist early. Otherwise, we trend clearer, just probably never fully clear. Even partly cloudy might be pushing it. Temperatures strive toward normalcy (mid-to-upper 40s these days), but snow pack may hinder that journey a bit. Mainly low-to-mid 40s still seems safer than going all in on “warmth” for now. Confidence: Medium-High
Tomorrow night: Missed the cold wind? It’s coming back as another Arctic front passes by overnight. There could be a few snow showers or a squall on this line, but likely of considerably less interest than prior snow squall events. Anyone who sees snow could pick up a dusting or so though. Lows dip to the mid-teens to low 20s across the area. Wind chills are probably mainly back in the single digits to near zero. Joy. Confidence: Medium-High
A LOOK AHEAD
On Monday, we take the brunt of the next Arctic attack. The main good news with these cold February days is that they’ve been rather sunny, and the sun is noticeably stronger this time of year than in January. Victories where we can get them! Highs may struggle for 20 in the suburbs while probably heading for the low-or-mid 20s downtown. Wind chills are low, apparently as usual. Confidence: Medium
Coming off lows in the single digits and teens, it’s another cold one Tuesday. We should again see a lot of sun, and probably less wind than Monday. Afternoon readings are in the upper 20s and low 30s. Comparatively balmy! Confidence: Medium
SNOW POTENTIAL INDEX
A daily assessment of the potential for at least 1 inch of snow in the next week, on a 0-10 scale.
9/10 (↑): Light to moderate snow accumulation is a strong bet today before an icy mix into tonight.