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Posted at 2:15 PM ET, 08/16/2010

A new work week, another severe t'storm watch

By Capital Weather Gang

* CWG's Full Forecast | Radar, lightning & more: Weather Wall *

The National Weather Service has issued a Severe Thunderstorm Watch for the D.C. area, in effect until 10 p.m. The Storm Prediction Center places the metro area within a bull's-eye of CAPE, a measure of instability in the atmosphere. From the Storm Prediction Center:

Radar & lightning: Latest D.C. area radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.


Thunderstorms are already starting to form in southwestern Loudoun and northwestern Fauquier counties, with storm activity expected to increase and migrate eastward during the afternoon into evening. Ballpark estimate: 4-8 p.m. looks to be the busiest time for storms across the immediate metro area.

See CWG's latest Full Forecast. And check back for updates through the day.

By Capital Weather Gang  | August 16, 2010; 2:15 PM ET
Categories:  Alerts  
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For those of you wondering what "CAPE" means, it stands for "Convective Available Potential Energy." Consider anything above 2000 an indication that conditions may be conducive to thunderstorms, possibly severe.

Posted by: afreedma | August 16, 2010 2:21 PM | Report abuse

Are we talking potential for serious storms like last week? I realize that an 18-wheeler truck going 65mph can cause MoCo to have a power outtage, but seriously, is there that chance, again?

Posted by: authorofpoetry | August 16, 2010 2:40 PM | Report abuse

Probably a moot point given current readings, but we can get severe with lower than 2,000 CAPE, usually ~1,000 will do the job... of course it is only part of the equation.

Posted by: Ian-CapitalWeatherGang | August 16, 2010 2:44 PM | Report abuse

Is there a site that has the current CAPE reading for the DC area?

Posted by: snowedin85 | August 16, 2010 2:49 PM | Report abuse

What's the highest CAPE reading we're apt to see hereabouts during the course of a year? I gather a reading of 2500 isn't chump change??

Posted by: JerryFloyd1 | August 16, 2010 2:50 PM | Report abuse

snowedin85, SPC has a forecast tools page -- here is one sector that covers us. If you go to the thermodynamics dropdown and select mixed-layer cape you can pull the type mentioned here. Jerry, 2,500 is very high for around here, don't know highest but I don't really recall much or anything aboe 3,000.

Posted by: Ian-CapitalWeatherGang | August 16, 2010 2:54 PM | Report abuse

Now, these have to be taken with a grain of salt, as they tend to grossly overestimate CAPE values, but soundings that are estimated hourly from satellites are available here:

Posted by: Brian-CapitalWeatherGang | August 16, 2010 3:01 PM | Report abuse

If I recall, the massive storms that hit us last Thursday had a momentary CAPE value of over 5,700 recorded at DCA, which is astronomical for this area. Right now, They seem to be hovering around 3,000 - 3,500, which is pretty shocking too. All signs point to the possibility of damaging storms forming very quickly, but for reasons unknown to me, they are still hanging back out in the foothills.

Posted by: marklandterrapins | August 16, 2010 5:18 PM | Report abuse

I had never heard of CAPE before reading this blog. Very cool information! Now one more thing for me to obsess over...

Posted by: rosilandjordan | August 16, 2010 8:30 PM | Report abuse

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