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Posted at 02:15 PM ET, 07/11/2011

Heat advisory Tuesday, storm threat tonight

Heat advisory noon to 8 p.m. Tuesday

Area covered by heat advisory Tuesday afternoon.
A heat advisory has been issued for the metro region from noon to 8 p.m. Tuesday. High temperatures are likely to reach the upper 90s to around 100. Factoring in the humidity, it is projected to feel as hot as 102 to 106.

Before this heat takes hold, a complex of thunderstorms, with a long history of producing damaging winds, could impact the region tonight.

The storm complex, or mesoscale convective system, is currently moving through central Ohio. If it holds together, it would probably impact the metro region some time between 7 p.m. and midnight.

There is 70% chance of the presence of ingredients needed to support severe thunderstorms this evening (NOAA Storm Prediction Center, SREF model)
The storms probably won’t be as intense as they were in Chicago and Detroit, as they’re going to run out ahead of the upper level support that helped energize them. Nevertheless, several indices which help forecasters assess the risk of thunderstorms based on a combination of factors suggest the storms still could be severe.

The illustration to the left illustrates that there is 70% chance of the presence of the ingredients - namely instability and wind shear - needed for severe thunderstorms this evening around the region (i.e. that the Craven-Brooks significant severe weather parameter will exceeed 20,000 m3/s3). Note: this does not mean there is a 70% chance of severe thunderstorms - it just means there’s a good chance the atmosphere could support them if they survive their journey through the mountains - about a 40-50% chance.

Dew points at 2 p.m.
Any storms will have plenty of low level moisture to work with - as you can no doubt tell by the sky high humidity levels around here. Dew points today are in the low-to-mid 70s - with even some upper 70s to the south.

If you’ve forgotten how to interpret dew points, here’s a chart we posted a couple years ago which serves as an easy-to-understand guide:

Dew point
How Humid it Feels (and subjective description)
Below 55 Dry (Pleasant)
55-60Hint of humidity (Still comfortable)
60-65Moist (Tolerable)
65-70Sticky (Becoming unpleasant)
70-75Muggy (Gross)
Above 75 Sultry (Oppressive and unbearable)

Humidity levels will be similarly high tomorrow, and the storm risk returns. Of course, many will anxiously await the storms to snap what could be record-breaking heat. Tuesday’s record highs of 99 (from 1908) at Reagan National, and 97 at BWI and Dulles (from 1908 and 1986) will all be in play.

By  |  02:15 PM ET, 07/11/2011

Categories:  Latest, Extreme Heat

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