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PM Update: Chance of a storm this evening, cooling down some Wednesday

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Our first 90-degree day of 2014 is in the books, but this surge of heat will prove short-lived.  A back door cold front slipping through the region tonight cools us down 10-15 degrees or so by Wednesday.  Before it passes, a thunderstorm is possible this evening.

Through Tonight: There’s a 30-40 percent chance of storms this evening, with the highest chances west of I-95.  Some of the storms could produce very heavy rain and strong wind gusts.  (See additional discussion below).  After sunset, the storm threat fades, with partly to mostly cloudy skies and mild conditions.  Lows drop to near 60.  Towards morning, some fog is likely to develop.

Tomorrow (Wednesday): Thanks to a marine layer (from moist flow off the ocean), expect low clouds, fog, and even some drizzle when you get up and head out.  Skies gradually brighten into late morning and midday, and some sunshine may emerge in the afternoon.  Highs are mostly in the 70s (lower 70s to the northeast and near the Bay and upper 70s southwest), but may push 80 with enough sun (especially southwest).  Late in the afternoon and early evening, there’s a 20 percent chance of a few showers and storms, especially in the western and southwestern parts of the region.  Winds are from the east at 5-10 mph.

See Matt Rogers’ forecast through the weekend. And if you haven’t already, join us on Facebook and follow us on Twitter . For related traffic news, check out Dr. Gridlock.

Pollen: Tree counts are HIGH at 421 grains per cubic meter.  Grass counts are MODERATE-HIGH, mold counts are MODERATE-HIGH and weed counts are LOW.

More on tonight’s storm potential:  CWG severe weather expert Jeff Halverson shares the following thoughts…

1.  Plenty of convective available potential energy has built in over our region but it appears to be capped – we are sitting in the center of a ridge, likely with some degree of subsidence warming and drying;

2.  Backdoor front is approaching Baltimore/Bay region and the Bay Breeze front is pushing west across Prince George’s County/eastern Montgomery (you can see these boundaries in visible satellite loop) – these could be triggers for convective activity;

3.  Mountain thunderstorms will probably remained anchored to the western slopes;  activity could still develop along eastern slopes, but as it drifts off it may fizzle

Bottom line:  Atmosphere is unstable but the ridge is suppressing convection broadly.  Boundaries and terrain will be key triggers;  activity that does fire likely to sit in place and rain heavily.

Cool animation of the back door front moving westward today from Delaware and northeast Maryland: While it was near 90 in D.C., the temperature in Ocean City, Maryland dropped into the high 50s.  You can see the progression of the front this afternoon in the animation below, generated by AccuWeather’s Jesse Ferrell…



Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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