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Posted at 10:00 AM ET, 06/30/2009

Forecast: Some Sun and Some Showers

By Jason Samenow

July 4th forecast mostly dry, for now...

* Outside Right Now? See Radar, Temps & More: Weather Wall *
* VORTEX2 Wrap-Up | Later: Dew Points for Dummies *


Today: Partly sunny. 30% chance of p.m. showers. 82-85. | Tonight: Partly cloudy. 60-67. | Tomorrow: Mostly cloudy. 40% chance of showers. 79-83. | A Look Ahead & July 4th


For most of the next six days, dry weather will rule. So while you may hear a lot about rain chances, they'll tend to be low. For every three days rain is in mentioned in the forecast, you may get wet just once. The other piece of good news is that the forecast for the holiday weekend looks better than this time yesterday, with mainly dry weather an increasing possibility -- but not a done deal...

Radar: Latest D.C. area 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 (Tuesday): We'll have a few more clouds and a touch more humidity (dew points near 60, rather than the mid-to-upper 50s) than yesterday, but generally pleasant conditions. Under a mix of clouds and sun, high temperatures will aim for the low 80s. Yes, a lonely shower or thunderstorm could (30% chance) fire up in the afternoon or early in the evening. Winds will be from the west at 10-15 mph. Confidence: Medium-High

Tonight: Any evening showers will rapidly dissipate after dark. The rest of the evening will be partly cloudy, with lows near 60 in the cooler suburbs, with mid-to-upper 60s downtown Confidence: Medium-High

Keep reading for the forecast through the weekend....

Tomorrow (Wednesday): A disturbance will swing through the region, probably giving us our best chance of afternoon/evening showers and thunderstorms of the week, but just around 40%. Outside any showers/storms, we'll probably have more clouds than sun with highs in the upper 70s to low 80s depending on how much sun is able to sneak through the cloud canopy. Confidence: Medium-High

Tomorrow Night: Showers will gradually diminish after dark, with a pleasant evening thereafter. Lows will range from 60-65 (suburbs-city) under partly cloudy skies. Confidence: Medium-High


Thursday and Friday both look pretty nice. The upper level low to our north will be winding down, so afternoon shower and storm chances will drop -- down to about 20%. Both days will have considerable sunshine with partial cloud cover, and highs in the mid-80s. The overnights will be dry with temperatures 60-67 (suburbs-city). Confidence: Medium-High

The forecast for Independence Day is pretty good at the moment. A stalled front may be far enough south and east to suppress most thunderstorm activity -- though it bears watching. I'll call for partly sunny skies, with only a 20% chance of late afternoon or evening thunderstorms. Highs will most likely be in the low-to-mid-80s. Partly cloudy overnight, with lows in the 60s.Confidence: Medium

Sunday will probably also be dry, with just a 20% chance of late day storms. High temperatures may be a little warmer, climbing to the mid- or possibly upper 80s. Confidence: Low-Medium

By Jason Samenow  | June 30, 2009; 10:00 AM ET
Categories:  Forecasts  
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Next: Dictating the Superiority of Dew Point

Comments just clouded up in the hour or so I've been at my computer & watching TV...and we are now having a pretty good rain shower.

Re my separate remarks on precipitable water, please see my comments in the post on dew points. Precipitable water is a necessary but not a sufficient condition for precipitation; you also need to have a triggering mechanism. There's plenty of precipitable water in the air over the Persian Gulf, yet Kuwait, Bahrain, Qatar, the Emirates and coastal Saudi Arabia and Iran are a desert. The subtropical ridge sitting over the Arabian subcontinent keeps the triggering cold-air pools and vorticity lobes out of the Middle East, especially in summer. Thus the Persian Gulf region tends to be a mighty uncomfortable desert with high temperatures, humidities and heat indices but little upper-air instability which might serve to trigger precipitation. As for us, we're sitting under a cold air pool unusual for midsummer, and the resulting instability is causing our daytime showers as warm surface air rises into the cold pool above.

Posted by: Bombo47jea | June 30, 2009 2:06 PM | Report abuse

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