From the ABC 7 Weather team

Archive for December 2014

Coastal Storm Brings Wet Weather Beginning Monday Night

December 7, 2014 - 05:58 PM
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It's been a grey start to December, but we finally saw a nice, clear day today.  This was the first fully sunny day since November 21st!  Soak up the sun early tomorrow morning because clouds will quickly thicken, as our next weather system approaches the area.

A developing area of low pressure, off the coast of the Carolinas, will increase cloud cover through the day Monday.  With the clouds, temperatures will only reach the mid 30s by the afternoon.  Here is a look at forecast highs on Monday.

Forecast Highs Monday

Both the morning and evening commutes will be dry, with wet weather from the coastal storm arriving after 8 PM.  Temperatures won't fall much overnight Monday into Tuesday, in fact, temperatures may actually climb a few degrees with an easterly wind component.  Check out our local simulation of radar at 10 PM Monday (1st image below) and 6 AM Tuesday (2nd image).

Local RPM Model Monday 10 PM
Local RPM Model Tuesday 6 AM

This model depicts all rain, which seems to be the trend among most guidance.  As the coastal low tracks farther north Tuesday, there may be a brief transition to snow late Tuesday night well NW of D.C.  Little to no accumulation is expected.  In fact, by Tuesday at 8 PM the coastal storm will be greatly impacting New England.  Here is a simulation of the coastal storm at 8 PM Tuesday.

Surface Features Tuesday at 8 PM

This will be a predominately rain event for us with the greatest snow potential over interior New England.  Check out forecast snowfall accumulations by Thursday afternoon.  Areas shaded in pink could receive over 10" of snow.

WxBell GFS Forecast Snow Total By Midday Thursday

The area of low pressure will get cut-off from the jet stream midweek and will spin freely over New England through at least Thursday.  That means added clouds for us Wednesday and Thursday with possible light rain and snow showers. 

There are still uncertainties to the forecast, since the coastal storm has yet to develop.  The Stormwatch weather team will continue to update the forecast, as new information becomes available. 

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More unsettled weather for the weekend ahead

December 3, 2014 - 05:34 PM
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The pattern doesn't appear like it will change anytime soon after bringing nearly an inch of rain to parts of the region Monday night into Tuesday and clouds on Wednesday. Thursday should experience a lull in the action, just in time for the National Christmas Tree Lighting, which Chief Meteorologist Doug Hill will be out live broadcasting tomorrow evening.

At this point we are expecting some sunshine in the morning hours followed by afternoon clouds as the next system pushes in from the west. A few models have depicted the chance for a few showers late tomorrow night into Friday morning, but this should be a low probability at this point with the best chance south and west of D.C.

Water Vapor image with tomorrow's disturbance and Saturday's disturbance

Looking west, an area of low pressure has been bringing inches of rain to parts of California over the past few days. A bit of energy and associated moisture has spun off this system and will help bring clouds to our region Thursday afternoon through Friday night.

Thursday rainfall totals as of 5pm for parts of California

Another area of energy will push into Southern California tonight into Thursday morning. This disturbance will move across the U.S. and into the Mid Atlantic this weekend, increasing chances for rain Friday night into the day Saturday.

Precipitation forecast for Friday through Saturday evening

Beyond Saturday, there are stark differences in model depictions, with a few models spinning up additional areas of low pressure off the east coast and socking the region in clouds and precipitation Sunday and Monday, and another completely clearing the region out Sunday with sunshine and mild temperatures. We will get a much better handle on this forecast in the next 12-24 hours but at this point are content on keeping the rain chances in for Sunday and again Monday.

Forecast precipitation Saturday through Monday Evening

 

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Winter Weather Advisory for parts of the D.C. area Tuesday

December 1, 2014 - 03:27 PM
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A cold front will sweep through the region on Monday afternoon/evening. Temperatures will fall behind the front, eventually ending up in the 30s for overnight lows!

Cold front will move through Monday afternoon/evening bringing a threat of isolated showers and dropping temperatures.


Eventually that front will stall just to the south of the region. An area of low pressure will ride along the front Monday night into Tuesday bringing precip with it. At the same time, high pressure will move front the Great Lakes region to the New England area. Eventually this evening, our winds will shift to the north and east bringing moisture and cooler air off the Atlantic Ocean and right into our area. What happens is, that moisture banks up against the mountains to our west creating a “cold air damming” affect or CAD. This set up generally makes forecasting that much more difficult, especially when determining precipitation types because that colder air will slide right under the warm air aloft which would make the precip type more of that of a wintry mix (freezing rain/sleet).

Winter Weather Advisory from 1am Tuesday to 1am Wednesday

Just around daybreak and into the morning commute, we will start to experience some spotty sleet and freezing rain, mainly north and west of D.C. (Loudoun County and Central and Western Montgomery County and points northwest). Inside the beltway, along I-95 and areas to the south and east, this event mainly looks like a very cold rain event but I can’t rule out some isolated pockets around D.C. of the wintry mix.

This is NOT looking like a major event but since it comes for the morning rush, there could be some problems (as there tends to be, even if it is just plain rain). And we are really not expecting that much to accumulate at all, perhaps just a glaze in some areas. Surface road temperatures, especially around the D.C. area, are above freezing so just like last Wednesday, any frozen precip that falls will have a hard time sticking. However, north and west of town on some rural roads, elevated surfaces (bridges and overpasses) and even exits could have some slick spots.

In-house model of Tuesday morning (rain = green, wintry mix = pink)


Again, I do not think this is going to be a huge event but I don’t want it to take anybody by surprise when our temperatures do not make it out of the 30s tomorrow (considering we are around 70 in a lot of the area on Monday).

Warm air will start to erode the shallow layer of cold air and any wintry mix will turn to plain rain by the afternoon hours. Most of the precipitation should move north around the kickoff of the evening commute but I do expect there to be some drizzle and fog around the region – there could even be some freezing drizzle at the high elevations). Temperatures rebound into the lower 50s on Wednesday but another bout of precipitation could be on the horizon for Friday.

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