D.C. area forecast: Mix ends this afternoon; iciness possible Tuesday night, weekend storm threat

Winter weather advisory into this afternoon for Loudoun county *

Winter storm warning far north and west including Frederick and Carroll counties  *

Link: Snowfall totals from National Weather Service

Overview points for today’s storm:

  • Mostly rain in the immediate metro region, possibly mixing with or briefly changing to sleet and snow before ending. Little or no accumulation.
  • Rain mixing with and changing to snow but just trace accumulations to a couple sloppy inches in our colder suburbs in Loudoun, northern Montgomery, and western Howard counties.
  • Accumulating snow of several inches or more in northwest Virginia and northern Maryland, including Winchester and Frederick (see accumulation forecast map in 7:35 a.m. update below)
  • Precipitation rapidly exits early this afternoon.

12:15 p.m. update: I confess, light precipitation may continue for another hour (or two northeast) longer than I thought (see previous updates) – especially in our northern suburbs – but it is generally waning in intensity.  (My earlier idea of the precipitation winding down early this afternoon was probably more accurate.)  North of I-66, a lot of the precipitation falling now is in the form of sleet and/or snow, but with the exception of western Loudoun and Frederick counties, it’s too warm and not heavy enough to stick.

To the south, steady precipitation has ended, but a few rain/snow showers may come through in the next hour or two.

This storm has been quite the rain-maker.  Reagan National has picked up 1.4″, a record for the date (besting the old record of 1.1″).  Dulles has picked up 1.29″, also a record (old record 1.07″).

As the worst of this storm has passed, this will be the last update.  We’ll have a new post on the Tuesday night and weekend winter weather threats around 1 p.m.

11:50 a.m. update: As precipitation starts to wind down, we’re getting reports of sleet and snow mixing with rain, even inside the Beltway.  There are no concerns about sticking/iciness with temperatures will above freezing. If you live south and southwest of D.C., your precipitation is more or less over – although a sprinkle or shower can’t be ruled out into the early afternoon.  North of I-66, the steadier precipitation wants to hang around a bit longer but should gradually diminish over the next hour.

Note: the winter weather advisory was dropped for Montgomery and Howard counties due to the lack of disruptive frozen precipitation.

11:10 a.m. update: One more band of moderate rain is pushing through the immediate metro region, with light to moderate snow in western Loudoun and Frederick counties.  Precipitation will decrease in coverage and intensity over the next hour from west to east.  In our northeast suburbs, it could keep going a bit after noon, but should be done by 1 p.m.

10:24 a.m. update: The storm is really moving fast and models indicate little precipitation, if any, falls after noon.  In western areas, precipitation is already beginning to taper off and could be done by around 11 a.m.  The rest of the area may well the precipitation end between 11 a.m and noon, from west to east.

10:10 a.m. update: Snowfall total reports from the National Weather Service from the National Weather Service indicate the heaviest totals have occurred in northern Maryland (as expected). In Allegany County, Maryland – where 6 to 8 inches accumulated.  In Washington and Frederick counties, generally 2-4 inches have been reported.

10:05 a.m. update: We’re getting some reports of sleet in the northern and western half of Montgomery County, and even some snow around Damascus. Although there may be some brief slushiness in this area, this shouldn’t be overly disruptive as this storm is trucking.  The heaviest precipitation has already passed to the east and we can start to see signs of the back edge along the I-81 corridor in western Virginia.  So even in areas of Frederick and western Loudoun county where it’s snowing, don’t expect a lot of additional accumulation (more than 1 inch or 2).  For a lot of the region, precipitation could even start tapering off prior to noon.

9:25 a.m. update: Let’s talk about the rain for a second. Through 9 a.m. Reagan National and Dulles airports had picked up 1.14″ and 1.15″ respectively. That would’ve been some serious snow. Speaking of snow, it continues accumulating in western Loudoun and Frederick counties.

 

 

9:00 a.m. update: The rain-sleet-snow transition area spans from near Bel Air to Reisterstown to Mount Airy in Maryland and then bends around towards Leesburg and into The Plains in Virginia. Just to the north and west of this line, conditions are starting to turn a bit slick.

 

The rain-snow line may continue to edge south-southeast towards Towson, Germantown and around Sterling over the next hour, but the wintry precipitation in this transition zone will probably more conversational than high impact (problematic on roads). To get into the more substantial snow and difficult driving conditions, draw a line from Winchester to south Frederick (Md) and up towards Westminster. Here are some photos from that zone.

 

8:05 a.m. update: We are seeing reports of snow and sleet creeping south-southeastward, with snow and sleet now advancing into Lovettsville, Purcellville, and Middleburg.  We’ve even received a report of some sleet around Gaithersburg.  In short, even though we lowered totals in some of our northern and western areas and don’t expect a high impact, wintry weather is still like there along with some slick roads over the next several hours. Meanwhile, snow continues to increase around Frederick County where several inches of accumulation are likely.

 

7:35 a.m. update: Even in our colder suburbs, temperatures are struggling to fall meaningfully, and the rain-snow line hasn’t moved much south of Frederick in Maryland or east of Clark County in northwest Virginia. In other words, this may be a bust for Loudoun County, western Montgomery County, Howard County, and western Fairfax County where we had said up to a few inches were possible. Here’s a revised accumulation potential map based on the current state of affairs (scroll farther down for our previous accumulation map to compare).


Capital Weather Gang snowfall accumulation forecast issued 7:30 a.m. Monday

For most of the area, except north and west of Frederick, this is increasingly looking like mostly a rain event, although some sleet and snow may creep southeastward and eventually reach the immediate D.C. area before ending early to mid-afternoon. For Loudoun, northern Howard and northwest Montgomery County – a little snow accumulation could still occur (and may not), but it shouldn’t cause huge problems.

Some slushiness is being reported around Round Hill in western Loudoun.

 

6:30 a.m. update: Dual polarization doppler radar has a product which provides a great approximation of the rain/snow line. (It’s called correlation coefficient, for a nice lay person’s explanation, click here). In the image below, the rain/snow line pops out prominently as the yellow line separating the two red regions – basically cutting through western Loudoun county and then into Frederick and northeast into central Carroll county.


Approximation of rain/snow line (via dual-polarization radar) at 6:20 a.m. (RadarScope)

6:15 a.m. update: Based on models and observations this morning (temperatures well above freezing, upper 30s to near 40 at 6 a.m.), we can take the “boom” scenario off the table in terms of meaningful snow in the immediate metro area and do not expect widespread road and travel concerns (although heavy rain and eventually mixed precipitation may slow things down a bit).

Snow and/or sleet that falls will likely be “conversational” (mostly not sticking, except perhaps slushiness on grassy areas) and the changeover from rain – if it occurs – may take into mid-to-late morning. In our colder suburbs to the northwest (Montgomery, Loudoun and Howard counties) in the advisory area, we favor the low end of our forecast snow totals in the map below, with a gradual transition to mixed precipitation and snow in the next couple of hours.

 

 

We continue to expect significant accumulating snow in northern Maryland, where a changeover from rain to sleet and snow is ongoing. Already, some locations in western Maryland (Allegany County) have received 1-4 inches.

5:15 a.m. update: Moderate to heavy rain is bursting into the area but temperatures – at the moment – are too warm for frozen precipitation (except in western Maryland and West Virginia, where snow has begun). At 5 a.m., Reagan National was 42, and Dulles 38, with rain. To the north and west, Frederick and Hagerstown both had rain at 37 and 33. Per our forecast below, these colder areas should begin mixing with and changing to sleet and snow over the next hour or two.

 

 

Overnight, the National Weather Service lowered its snowfall forecast around the metro region and its now more or less in line with ours – on the lower end. Still, conditions – especially our colder suburbs – will change quickly this morning, so monitor them closely and allow for the possibility you may need to allow some extra time to get places. Our next update will be in another hour or so.

*** Read below for the full forecast through the weekend, published at 5 a.m. – although note today’s forecast has been revised per updates above ***

Today’s Daily Digit

A somewhat subjective rating of the day’s weather, on a scale of 1 to 10.

2
A sloppy mix of cold rain, sleet, and pasty snow doesn’t excite this snow lover.

Express Forecast

Today: Rain, sleet, and snow, ending in the afternoon. Highs 35-40.

Tonight: Mostly cloudy. Lows: 25-30.

Tomorrow: Mostly cloudy. Highs near 40.

FORECAST IN DETAIL


Radar & lightning: Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Expect a little bit of everything  (even the unexpected?) this morning as a complex but intense storm bolts through the region. The D.C. area sits right on the rain-snow line which gradually creeps southeastward.  Rain comes first but mixes with and changes to sleet and snow, especially north and west of the Beltway, where the accumulation prospects are highest.

The storm pulls away this afternoon, but we don’t catch much of a break before the next storm system arrives Tuesday night, with more mixed precipitation possible in our colder areas.  Our respite arrives midday Wednesday into Friday, but the third in this week’s parade of storms may cause trouble this weekend.

Temperature Map

Temperatures: Latest D.C. area temperature map. See interactive map on our Weather Wall.

Today (Monday): Most everyone starts the day with rain, but in Loudoun and Frederick counties, the rain should fairly quickly begin to mix with and change to sleet and then snow between about 5:30 and 7:30 a.m.  In northern Fauquier, western Fairfax, Montgomery and Howard counties, the transition to frozen precipitation probably occurs in the 6:30 to 8:30 a.m. window. Elsewhere, the changeover to sleet and snow from rain occurs more slowly and may not complete itself, especially from downtown and to the south and east.

Precipitation falls intensely at times through late morning, and heavy, wet snow may start to pile up, especially in northwest Loudoun, Frederick and western Howard counties.  Closer to the District, accumulation prospects are  iffier and more rain/sleet may fall, but sleet could cause some slick spots, and conditions will need to be closely monitored, so stay tuned to our live updates above.

Temperatures this morning range from 31-37 (northwest to southeast) across the region.  By early afternoon, precipitation rapidly begins to taper off, with highs 35-40. Light winds from the north at around 10 mph. Confidence:Low-Medium


Capital Weather Gang snowfall forecast map issued 5 a.m. Monday morning

Tonight: Mostly cloudy skies with possible areas of fog. Lows range from the mid-to-upper 20s in the colder suburbs to 30-32 downtown. Winds are light out of the north.  Confidence: Medium-High

For related traffic news, check out Dr. Gridlock. Keep reading for the forecast through the weekend…

Tomorrow (Tuesday): Mostly cloudy (maybe some intervals of sun in the morning), and chilly, with highs near 40. Winds are light from the northeast at around 5-10 mph. Confidence: Medium-High

Tomorrow night: Rain develops between 8 p.m. and midnight, except possible freezing rain north and west of the Beltway.  Lows range from 30-34 (suburbs-city). We’re not expecting a major ice storm where freezing rain occurs, but a light glaze is possible.  We’ll have more on this after today’s storm winds down. Confidence: Medium

A LOOK AHEAD

Snow Potential Index

A daily assessment of the potential for at least ~1″ of snow in the next week, on a 0-10 scale.

5 (→) 50/50 chance of 1″+ today seems about right. Weekend storm still hanging out there.

Rain ends Wednesday morning (except freezing rain well north and west of the District in colder pockets of Loudoun and Frederick counties, perhaps) by around 10 a.m., followed by partly to mostly cloudy skies, and highs 45-50. Turning colder Wednesday night, with lows in the low 20s in the colder suburbs to the upper 20s downtown. Confidence: Medium

A quier stretch Thursday through Friday, with partly sunny skies and seasonably cool temperatures.  Highs both days are in the mid-30s to near 40, with overnight lows mainly in the 20s. Confidence: Medium

The weekend is a giant question mark right now, but low pressure developing in the Gulf of Mexico is likely to make a move northeast.  Precipitation, quite possibly in the frozen form (a wintry mix or snow) at least to start, has a good chance of moving into our area – but the timing could be Saturday or Sunday.  The exact track of the storm will determine whether and when any frozen precipitation turns over to rain.  Temperatures should remain on the chilly side, with highs in the 30s, and lows 25-30.  Confidence: Low-Medium

 

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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