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Posted at 5:00 AM ET, 08/20/2009

Forecast: More Heat, Humidity & Storm Chances

By Josh Larson

But cooling & drying trend will begin by (late) Saturday

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Today: Partly sunny & humid. P.M. storms? Near 90. | Tonight: Mostly cloudy & muggy. Storm? Mid-70s. | Tomorrow: Mostly cloudy & humid. P.M. showers/storms probable. Near 90. | A Look Ahead


If you disliked the weather over the past few days, you won't find solace in the near-term forecast. We hold onto unpleasant humidity levels and very warm temperatures today and tomorrow. That will juice up the atmosphere for scattered showers and thunderstorms both afternoons. When does relief arrive? Our oppressive air mass will not relent until a cold front (which will keep Bill away from the mid-Atlantic), accompanied by a possible line of storms, pushes it away on Saturday.

Radar: Latest regional radar loop shows movement of precipitation over past two hours. Powered by HAMweather. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Today (Thursday): With temperatures starting off in the mid-70s in most locations, and at least partly sunny skies through much of the first part of the day, temperatures will quickly climb to near 90 (or even a degree or two above in some spots) by early afternoon. Southerly winds of 10-15 mph will aid in continuing our uncomfortably high humidity. Clouds increase and scattered showers and thunderstorms develop (30-40% chance) as the afternoon wears on, some of which may produce heavy downpours. Confidence: High

Probability: 30-40%
Coverage: Scattered

Tonight: Mostly cloudy to overcast skies along with truly muggy conditions reigning supreme tonight. Widely scattered showers and thunderstorms may linger in some spots during the evening, and perhaps even overnight. Overnight lows won't drop below the mid-70s. Confidence: High

Keep reading for the gradually improving forecast through early next week...

Tomorrow (Friday): I'd plan on mostly cloudy skies on Friday, with continued uncomfortably high humidity. A few isolated showers or thunderstorms aren't entirely out of the question during the morning or early afternoon hours (30% chance), but I think most will hold off until later in the day (60% chance), when a couple could be of the heavy, gusty variety. Despite those mostly cloudy skies, afternoon highs will still rise to near 90. Confidence: Medium-High

Tomorrow Night: I'd bring an umbrella with you if you happen to head out for the evening Friday, as some scattered thundershowers (50/50 chance) may linger into the evening hours. It'll be another muggy night with temperatures bottoming out in the low to mid-70s. Confidence: Medium


Saturday is somewhat of a transition day, as a cold front tries to push through the mid-Atlantic. The wildcard at the moment, though, is timing. It appears likely that clouds and scattered showers & thunderstorms (50% chance) may mar the first half of the day, along with slightly cooler daytime highs in the mid-80s. I think we'll begin to see a drying out trend by late afternoon, though I can't rule out a few showers lingering into the evening hours -- mainly east of town. We'll see some late overnight clearing, with more comfortable overnight lows in the mid-to-upper 60s. Confidence: Low-Medium

The cold front should push far enough south on Sunday to allow high pressure to build back over the region, fostering a return to mostly sunny skies, noticeably lower humidity levels and dry afternoon highs in the mid-80s. Still, an isolated storm isn't out of the question. Clear and dry overnight Sunday, with lows primarily in the mid-60s. Confidence: Medium-High

At this point, it appears that high pressure will remain anchored over the area on back-to-work Monday, which should produce another very pleasant, dry day of mostly sunny skies, low humidity and comfortable afternoon highs in the low-to-mid 80s, along with overnight lows in the mid-60s. Confidence: Medium-High

Updated: Thursday Aug. 20 @ 5:35 p.m.

By Josh Larson  | August 20, 2009; 5:00 AM ET
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Hey CWG...looks like the chances of rain are morely for Saturday, but also that it would likely happen in morning or midafternoon, while clearing up and cooling off later in the day. Is that accurate? Still think we'll be able to get away with having our wedding ceremony outside in georgetown? at 6 pm? Thanks guys!

Posted by: zim94 | August 20, 2009 10:10 AM | Report abuse

zim94, I'm sorry to say that the most recent computer modeling, as of this morning, appears to have slowed down the progression of the front and suggests that showers & thunderstorms may very well last well into the second half of the day Saturday...and, perhaps, (worst case scenario) even into Sunday now, especially east of town :(

Posted by: Josh-CapitalWeatherGang | August 20, 2009 11:07 AM | Report abuse

Oy vey...that's bad news. Any second opinions out there?:) Might the front speed up?

Posted by: zim94 | August 20, 2009 11:36 AM | Report abuse


I mostly concur with Josh. Since yesterday morning the models have been consistent with showing at least the potential for shower/storm activity to last into Saturday p.m. At this point I'd say it's probably a 50/50 toss-up whether they finish up by early afternoon, or linger a bit longer. Any storms on Sunday would likely be isolated in nature, but still the potential is there, at least as far as the current data shows.

Posted by: Dan-CapitalWeatherGang | August 20, 2009 1:40 PM | Report abuse

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