* Winter weather advisory early Monday morning into Monday afternoon for Loudoun, Frederick, Montgomery and Howard counties *

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

9:50 p.m. update: The latest data suggest it’s going to be a real challenge for accumulating snow to extend inside the Beltway Monday.  Not only will ground temperatures likely remain mostly above freezing, but there may also be a warm pocket of air aloft that makes it challenging for snow to fall . Although there may be a little snow especially by late Monday morning (fat, wet flakes), rain and sleet may be the predominant precipitation types in the immediate metro area.  Still, even inside the Beltway Monday morning, expect a slow commute due to heavy rain possibly mixing with and changing to sleet. Some slick spots could develop if moderate to heavy sleet materializes.  Because we are so close to the rain/snow line and small changes could have significant impacts on the forecast, continue to monitor conditions and the latest forecast in the morning. Conditions across the region will likely vary widely with heavy snow in the northwest part of the area, heavy rain southeast, and a mixed bag in between.

If you draw a line from Leesburg, Va. to Clarksburg and head to the northwest, those are the areas with the best chance of significant snow.  In fact, our snowfall map (below) may be too conservative in northern Maryland towards the Mason Dixon line, where some double digit snowfall totals could occur.

Temperatures in the metro region at 9 p.m. still ranged between 45 and 50 degrees.  Out in Hagerstown, where heavy snow is possible, it had dropped to 42.  The cold front has come through the area (winds are now from the north), and temperatures are slowly declining, but the push of cold air probably isn’t strong enough to turn this into a big snow event in metro D.C.

We’ll provide live updates of the storm starting around 5 a.m. Monday  (we’ll only post additional updates this evening if needed).

6:00 p.m update: The afternoon models shed little light on this very complicated forecast. Our thoughts on this storm and accumulation prospects – as discussed/shown below – have not changed.  Temperatures this afternoon reached the upper 50s to low 60s –  so temperatures have a long way to cool for us to get snow. Having said that, today’s mild temperatures were expected (though they pushed a bit above forecast levels), so they don’t significantly affect our forecast for tomorrow even as they continue to represent a formidable obstacle to overcome for any accumulation in the metro area.

One thing we maybe haven’t mentioned enough is that in addition to the mix of snow and rain expected Monday morning, some areas may get periods of heavy sleet.  Heavy sleet can quickly cause roads to to become slushy/slick – something else to keep in mind.

We’ll have another update around 10 p.m. or so, after the Super Bowl. Enjoy.

From earlier this afternoon: Just what we needed — another winter storm to disrupt the beginning of a work week. We say that literally for snow lovers and school kids cheering for another delay, closure or early dismissal. And sarcastically for pretty much everyone else. Yet while accumulating snow (perhaps mixing with sleet) is possible for some late tonight into tomorrow afternoon, especially north and west of D.C., it is not a sure bet for everyone, especially from the District as well as points south and east.

Why so wishy-washy? Unlike with recent storms where it was cold enough to be sure of all snow and that all of it would stick, this time temperatures will be coming off highs in the 50s this afternoon, and it’s unclear how quickly and how far south and east into the area the colder air needed to support accumulating snow will push.

The map below shows our best guess forecast as of now. Note the relatively high “boom” and “bust” chances, because small differences in temperatures and/or precipitation intensity could make a significant difference in snow amounts either way. Also, make sure to read the timeline and key points further down.

Updated (slight changes from prior) CWG snowfall forecast for Monday Feb. 3. Issued Feb. 2 at 1:15 p.m.


6 p.m. to midnight tonight: 50% chance of light rain. Perhaps a light shower prior.

Midnight to 4 a.m.: Steadier rain becomes likely from west to east, especially after 2 a.m.

4-8 a.m.: Rain changes to snow (could mix with sleet) north and west of the Beltway, from northwest to southeast.

8 a.m.-12 p.m.: Areas inside the Beltway and to the south and east see rain change to snow (could mix with sleet) *if* cold air has enough momentum to the south and east and/or if precipitation is heavy enough. This is when the heaviest of the precipitation is likely across the area.

1-4 p.m.: Precipitation exits west to east.

Key points

*There looks to be plenty of moisture with this system, with models almost unanimously predicting near or past 1″ of liquid equivalent precipitation.

*With temperatures in the 50s to near 60 today and slowly falling into the 40s this evening, any precipitation this will begin as rain.

*A change to accumulating snow, perhaps mixed with sleet, is likely north and west of the Beltway early-to-mid Monday morning.

*Accumulating snow, possibly mixed with sleet, is a risk inside the Beltway and to the south and east mid-morning into afternoon, but not definite.

*A burst of heavy precipitation Monday morning could pull colder air down from above faster and result in more snow accumulation for everyone.

*On the other hand, if precipitation is too light, then much of the immediate metro area could see little or no snow accumulation.

*Any snow will probably be of the wet and slushy variety, not the dry powdery stuff we saw last time.

*Thanks to the wet nature of the snow, places north and west that get more than a few inches may see tree damage and power outages as time progresses.

Forecast soundings from this morning’s GFS for Monday at 7 and 10 a.m. near D.C. The thick blue line is the freezing line with the first panel a bit too warm (right of the blue line) for snow and the second likely snow (on or just left of the blue line). Very small temperature shifts, and intensity of precipitation, can make or break snow chances in the immediate area. (Twisterdata.com)

What does our Winter Weather Expert Wes Junker have to say?

The models continue to advertise a storm with an upper level pattern that favors development of a band of heavy precipitation. Our main problem remains one of trying to figure out how quickly the cold air will become deep enough to support a changeover from rain to sleet to snow. The far northwest suburbs and areas toward the Mason/Dixon line could end up with a significant wet snowstorm which could be heavy enough to cause tree damage or some power outages. However, areas inside the Beltway will probably deal with rain and sleet before a possible changeover to snow before the precipitation ends tomorrow afternoon, with only minor accumulation if any.

This is one of those cases where temperatures in the lowest 7,000 feet on various models are within a degree or two of freezing during the period of the most intense precipitation. That makes it extremely difficult to guess at exactly when any changeover might occur. Therefore, our confidence level concerning snowfall amounts in and around the city is on the low side.

We’ve opted to play our projected snowfall amounts in and around the city conservatively since this is the type of situation where we’ve been burned a few times over the past three years. In those cases either the precipitation rates never quite lived up to expectations or the cold air never reached the city quite as quickly as forecast. The December 9th storm earlier this winter is one recent example when the models spread cold air across the city much too quickly.

SchoolCast, FedCast, and TravelCast

Monday SchoolCast

(Loudoun, Montgomery, Howard, and counties N/W)

(2.5 apples) At least 50/50 chance of no school, delay, or early dismissal. Do your homework just in case, it’s not a sure thing.

(Everywhere else)

(1.5 apples) School should go on as scheduled except perhaps in counties with a history of closing or modifying the schedule for lighter amounts of snow. Keep an eye on the forecast and conditions as small changes may impact potential.

Monday FedCast

(2 domes) 50/50 chance of unscheduled leave policy. Shut down unlikely.

Monday TravelCast

(2.5 airplanes) Minor-major airport delays expected, mainly in the morning to midday.