Longest, strongest heat wave of summer (so far) peaking

The combination of heat and humidity climax today and Friday in the Washington, D.C. area. On both days, it will feel like 105 or hotter in the afternoon, and overnight temperatures will struggle to fall below 80 degrees in urban areas.

As of noon, the mercury had climbed to 94 in Washington, D.C., with a heat index of 102.

Heat wave is sprawling, widespread heat advisories and warnings

Heat advisories are in effect for not only the Washington, D.C. and Baltimore regions, but a massive area from the eastern Dakotas into New England (with a few gaps in between).  A few areas are under excessive heat warnings (in eastern Michigan, around Philadelphia and in southern New England) where the intensity of the heat is especially unusual.

Heat advisories (in orange) and excessive heat warnings (in magenta). (National Weather Service)
Heat advisories (in orange) and excessive heat warnings (in magenta). (National Weather Service)

Once again, D.C. at the epi-center of the heat

For the third straight day, the D.C. area has found itself among the hottest major cities outside the desert Southwest, if not the hottest.

Here are maps of heat indices and temperatures at noon, from weather.com

(Weather.com)
(Weather.com)
(Weather.com)
(Weather.com)

Record high nighttime (minimum) temp tied for 2nd straight day in D.C.

For the third straight day, the morning low in Washington, D.C. (as measured at Reagan National Airport) dropped to a mere 80 degrees.  And for a second straight day, that represented a tie for the record highest low temperature (assuming we don’t drop below 80 by midnight, which we shouldn’t).

On Wednesday, the low of 80 matched the record from 1983, and, this morning, the record of 80 from last year (2012) was tied.

Through noon today, the temperature had not dropped below 80 in D.C. for 76 hours.  It may remain above 80 into Saturday evening…an incredible 130 or so hours – closing in on the longest-recorded stretch established in 2011.

Hot air makes pollution worse

For the second straight day, the Washington, D.C. area has a code orange air quality alert in effect, which means the air is unhealthy for sensitive groups (older adults, young children, those with respiratory issues, etc.).

Climate Central created this nice graphic, using Washington, D.C. data from 2012, which demonstrates the relationship between hot weather and compromised air quality.


(Climate Central)

Most of the code orange (and only code red day) days coincided with temperatures above 90 degrees.

Relief?

The big cold front that will sweep through the region Saturday night into Sunday morning will shift the weather regime to one that gives us near normal to below normal temperatures next week.


(Weather.gov)
Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Kevin Ambrose · July 18, 2013