From the ABC 7 Weather team

Archive for February 2014

Next storm to affect areas northwest of D.C. Tuesday night

February 3, 2014 - 02:57 PM
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As one weak storm departs the region with light snowfall in its wake for parts of the area, it's time to focus on the next system, which will enter the region tomorrow night. This new system again looks to have wintry precipitation involved, but it appears like it will hit the same places that saw today's snow and leave D.C. with less of a threat.

Winter Storm Watch for parts of the D.C. area

A Winter Storm Watch is in effect for areas northwest of D.C. once again, with the biggest threat being up to a quarter of an inch or more of ice.

The next system will be different from today's, as low pressure will ride northeast along the spine of the Appalachians west of D.C. and a new area of low pressure will eventually form and take over off the east coast. *Nerd Alert* - You can impress your friends and tell them this will be a case of Miller Type B cyclogenesis.

Forecast 12Z GFS MSLP, 6hr precip and 850mb temps (Courtesy: NEXLAB Models)

High pressure will shift to the north of D.C. tomorrow helping supply cool, dry air at the surface through the day. Winds will shift to out of the northeast and a cold pool will begin to set up east of the mountains. Precipitation often acts to strengthen the cold pool as Cold Air Damming (CAD) takes over. You can see the CAD in the kinks in the isobars just east of the Appalachians in this model forecast for late Tuesday.

Warmer air will be located above the surface, with 850mb temperatures a few degrees above freezing, but at the surface, temperatures should be at or below freezing for much of the region at the onset of precipitation. This will lead to rain falling on frozen surfaces and freezing on contact.

4km NAM Forecast reflectivity for Wednesday morning around 1am (Courtesy: WeatherBell Models)

For the D.C. Metro and points southeast, temperatures should jump above freezing by sunrise, but a few slick spots may still be possible for the commute Wednesday morning. Areas northwest will have the opportunity for freezing rain to hang on in the region even longer, and significant icing may be possible along and west of the Blue Ridge Mountains particularly in the shallow valleys where cold air gets trapped at the surface.

We'll keep a close eye on this over the next 12 hours and have the latest updates on ABC 7 News at 5, 6 and 11pm.

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Latest thoughts on snow Monday in the D.C. area

February 2, 2014 - 03:15 PM
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A Winter Storm Warning goes into effect tomorrow morning and runs through Monday afternoon for areas north and west of D.C. A Winter Weather Advisory is in effect for roughly the same time period but for areas closer to D.C. such as Loudoun, Montgomery, Howard and northern Fauquier Counties.

Winter Storm Warning and Winter Weather Advisory in effect Monday

This system is still taking shape in the Mississippi Valley region and will move to the northeast towards the D.C. Metro for the remainder of the day. A cold front is currently moving through West Virginia and Pennsylvania but hasn't reached our area just yet. It is expected to move through the region later this evening and temperatures should fall rapidly behind the front from the 50s into the 40s and 30s.

4KM NAM Model forecast temperature tonight at 11pm (WeatherBell.com)

Above is a look at the forecast temperatures from the 4km NAM Model at 11pm. Move this along to 7am and you can see how fast the cold air gets into the region below. Temperatures closer to the Metro are still expected to be above freezing at this point and rain should still be the predominant precipitation type for D.C. and points southeast. Snow will be taking over in the northwestern suburbs.

4KM NAM Model forecast temperature at 7am (WeatherBell.com)

The problem is the region has experienced such mild temperatures now for a few days, so ground temperatures will continue to be above freezing. The other question is how cold will it actually get tonight into tomorrow morning? At this point temperatures appear to stay mainly above freezing in the D.C. Metro and points southeast. Even if it were to snow, it would have to snow very heavy for accumulations to occur.

Areas northwest of D.C. even have questions with temperatures as a few models are depicting temperatures at or just above freezing which would lessen snowfall totals.

NWS Baltimore/Washington Snow forecast

At this point, we think the D.C. Metro itself will see little snow with accumulations on the grassy surfaces. Areas just to the northwest of D.C. may see minor accumulations of 1-2 inches. But locations farther northwest such as northern Loudoun and Montgomery Counties and farther have the best chance for heavier accumulations (greater than 2") given the elevation and amount of cold air.

The graphic above is one of the many graphics the National Weather Service provides on their Winter Weather Page. Our team is currently in agreement with their snow range, though we have to warn that if cold air doesn't completely take over, snowfall totals northwest will be considerably less.

Precipitation amounts should be close to an inch through much the region, but a lot of it appears like it will fall as rain. With that in mind, I hope you didn't get your car washed this weekend!

Timing

Rain should start later this evening into tonight before changing over to snow in the northwestern suburbs by early tomorrow morning. It will take longer for the changeover to occur in the D.C. Metro and it may not even occur until the late morning to early afternoon.

All precipitation should exit the region by Monday afternoon around 4pm.

Worst Effects

Heavy, wet snow is possible well northwest of D.C. and travel is expected to become hazardous and closings will be possible. Have this in the back of your mind and don't get stuck in it if you're heading out early tomorrow morning.

As always, we'll be keeping a close eye on this system and will be updating around the clock and ABC 7 News. Be sure to tune in tonight and we'll be with you as well bright and early for Good Morning Washington. Enjoy the last few hours in the 50s this afternoon!

 

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