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Posted at 05:55 PM ET, 07/22/2011

PM Update: Historic heat and humidity broil region; excessive heat warning Saturday

Raising 2011 Sweat Ceiling, Dulles Airport sets all-time record high of 105; BWI’s 106 second highest all-time; isolated severe storms this evening

Excessive heat warning tonight and Saturday
Air quality Saturday: Code orange, unhealthy for sensitive groups
Heat wave & hot weather guide | Submit your hot weather photos

Record heat updates from 3:30, 4:00 and 5:20 and 5:30 p.m.: Dulles and BWI airports blew by old record high temperatures for the date (of 98 and 101) this afternoon, reaching 105 and 106, respectively. Dulles’ 105 is the hottest temperature ever recorded there, passing 104 from July 16, 1988. BWI’s 106 is the second hottest all-time there (it’s all-time hottest temperature is 107 from July 10, 1936) . Reagan National reached 102, one shy of its record. All three airports set (or tied, BWI) record high minimum temperatures this morning (barring an unforeseen cool down this evening). But the air temperatures are just part of the story. Reagan National’s heat index, factoring in humidity, reached 121 at 3 p.m., the highest known level since 122 on July 16, 1980. Excessive heat warnings remain in effect through 10 p.m. tonight and from 10 a.m. to 8 p.m. Saturday when dangerous heat is once again likely.

Forecast through tonight: A few strong storms may (20-30% chance) produce some cooling dowpours and gusty winds through this evening, primarily over the north and northwest suburbs (e.g. Loudoun, northern Montgomery, Frederick and Howard counties). Earlier storm updates But most places stay dry. Like last night, the combination of heat and humidity is oppressive well past midnight. In urban areas, temps stay in the 90s through around midnight with heat indices above 100. After midnight, temps slowly cool to the upper 70s in the cooler suburbs to the low 80s downtown. Record high minimum temperatures of 81, 79, and 73 at DCA, BWI, and Dulles are all in jeopardy.

Forecast for tomorrow (Saturday): One more brutal day. High temperatures sizzle to 99-103, with heat indices of 110-117. Towering cumulus may develop in the afternoon with scattered thunderstorms possible (30% chance) late and into the evening. Some of these storms may be strong to severe given all the instability. Record highs Saturday are 101 at National, 102 at BWI and 99 at Dulles.

See Camden Walker’s forecast through early next week. And if you haven’t already, join us on Facebook and follow us on Twitter

New York/New England heat: The furnace-like heat blasted its way up the coast, with triple digits already observed in the Boston area, in addition to DC, Baltimore, Philly, and the New York metro area. Newark, NJ smashed its all-time record high temperature of 105, and stood at 108 degrees at 3 p.m. That is just 2 F shy of the all-time state record for New Jersey, which is 110 F. According to a tweet from @weatherchannel, New York City’s Central Park stood at 104 F at 3 PM, which is the hottest reading there since 1977, and the 104 F reading in Atlantic City, NJ was the hottest there since 1969. Boston hit 103, its hottest day in 85 years. And Hartford’s 103 was an all-time high for that city. - Andrew Freedman, Jason Samenow

Pollen update: From Walter Reed - “Nettle family, plantain and the chenopod/amaranth (lambs qtr/pigweed) pollen group continues to dominate the pollen count in spite of the heat wave. Our weed count is LOW (NAB range) at 7.35 gr/cubic meter, which is moderate for our local area count. There has not been any ragweed pollen spotted yet, however, ragweed season is not far off. A lone linden pollen accounts for the LOW tree reading at 0.32 gr/cubic meter. Grass pollen is LOW at 1.6 gr/cubic meter and mold spores are MODERATE at 7419.31 spores/cubic meter.”

Earlier storm updates

5:25 p.m. UPDATE: Some pop-up storms are presently in central and northeast Fairfax county, northern Fauquier county and northwest D.C. Isolated storms may continue to flare up and fizzle for the next couple of hours. Follow our Twitter feed above for the latest.

5:00 p.m. UPDATE: Storm in the vicinity of Potomac (mentioned below) has weakened (no longer severe) and is drifting east toward 495 and I-270 junction. It may miss the District. A second storm has developed north of Fairfax and is slowly sinking southeast into Fairfax and towards Annandale. Some additional isolated storms have popped up in Loudoun county.

4:30 p.m. UPDATE: The hot atmosphere is fueling some isolated strong to briefly severe storms. A severe thunderstorm warning is in effect until 5:15 for northeast Fairfax county, southeast Montgomery county, northwest D.C., and north Arlington. Storm likely to produce some downpours and dangerous lightning and may produce damaging winds. Areas most likely to affect include: Bethesda/Potomac, McLean, and Georgetown.

By  |  05:55 PM ET, 07/22/2011

Categories:  Forecasts, Local Climate

 
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