From the ABC 7 Weather team

Snow chances in D.C., MD and VA over the next few days

January 11, 2012 - 04:44 PM
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More snow looks possible in the coming days in the D.C. area. Here's what you can expect.

It's been a nasty day in the D.C. area with periods of rain and chilly temperatures but it's the forecast ahead that's very unique with big temperatures swings and the chance for some more flakes adding up to the second or possibly even third time this week!

First things first, check out the size of this system that's bringing all of this rain. Check out the video of it as well, really neat. Ok weather nerds out there, this could be a little on the lengthy side, so hold on to your hats.

850mb Temps for this morning

I wanted to show you a couple maps we typically look at to show why this is an interesting set up. There are numerous factors at play right now including 2 surface lows, a strong upper-level low, and another following trough that will eventually give the D.C. area the chance for some white stuff. Above is the 850mb Temperature map for this morning. The colors denote the temperatures, which you can see are relatively mild on the east coast and much colder through the Northern Plains. The light blue area over Mississippi is where the upper-level low was located.

500mb Vorticity Plot from this morning

Now take a look at the 500mb vorticity plot from the same time period. This shows areas of strong vertical motion in the atmosphere and generally denotes where areas of unsettled weather will be given the right conditions. As expected, this corresponds nicely with the colors from the 850mb temperature map, with strong rising motion over the upper-level low around Mississippi as well as where the trough is diving into the Northern Plains.

850mb temps early Friday morning

Three more maps to go through to give you an idea of our thoughts. We now fast forward to Friday morning just after midnight to the 850mb temperatures. The main thing we see is the progress of that extremely cold air originally over the Northern Plains. The upper-level low and it's surface counterpart have set up over the Great Lakes, helping to circulate that colder airmass around the low into our region. The surface cold front will be knocking on our doorstep and there's plenty of energy associated with it.

Vorticity map early Friday morning

Now check the same time period with the 500mb vorticity map. What a difference a little more than a day makes! See that tiny little blip just to the northeast of Maine? Yea that's what's left of the low from Wednesday. The northern Plains energy has formed into a massive trough which was originally positively tilted and now is beginning to change to a negatively tilt which shows signs of strengthening. With all of that energy located just to our west, there will be plenty of rising motion which could mean precipitation for our area. That is really where the main question lies. With strong southwesterly winds and temperatures above freezing at 850mb (see above) any precipitation appears like it will begin as rain, but as that cold front moves into our region temperatures will take a dive in a hurry and rain may change to snow at the worst possible time.

Surface map early Friday morning

We'll get to something a little less weather-nerdy now, as the surface map above shows the predicted features Friday morning. Note the green area just to the northwest of D.C. where much of the energy is associated with that strong vort to the west. We think there is the potential for some of that precipitation to change over from rain to snow as the front moves east. The exact pinpoint location of this will vary but we should tie it down by tomorrow afternoon.

My Main Thoughts and Concerns:

The chance for snow will be very brief and only light amounts will be possible (below an inch). Any higher amounts (MAYBE an inch or more) will be in the higher elevations to the north and west of the city. Drastically higher amounts will be likely for the ski resort areas on the western slopes of the Alleghenies.

What do we have going for us? Temperatures overnight Thursday into Friday morning should be quite warm and road temperatures should be well above freezing when and if snow begins to fall. Precipitation should also begin as rain before changing over, making for wet roadways which will make it tougher to support measureable snow.

What concerns me? Uhh, it's Friday the 13th people. Doesn't that concern us all? Ok, not only that but snowfall could occur at the worst possible time during the day, just prior to the morning commute around 4am. This means if there is a strong enough burst, there may be the potential for snow to coat a few of the roadways and possibly some of the local bridges and overpasses. That would mean one heck of a bad way to start your Friday, which is why I took the time to tell you all of this in a short, concise blog post. We'll have much more on this tomorrow.

Quick Outlook Beyond: Friday looks windy and cold with highs only near the 40 degree mark. The weekend will see more of the same with highs probably only in the upper 30s each day and another chance for flurries with a clipper on Sunday.

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