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Matt Ross @ 12:00 AM


Today will be our hottest of the year and since August of 2002 as temperatures will near the 100 degree mark under sunny and hazy skies
. While slightly less humid than yesterday there will be no relief in sight as heat indices near or surpass 110 degrees. As such, the National Weather Service has maintained the Heat Advisory issued yesterday. I would put the chances of hitting the century mark at about 25% thus making it unlikely to tie or beat the record of 103 for the date.

The most likely scenario is highs of 96 to 98 degrees for most of the metro area due to both elevated humidity levels, and high soil moisture content resulting from the 5-7" of rain across the area so far this month. Although the last 2 summers have failed to see the upper 90s, more often than not any given summer will see at least several of these days. 100 degrees is a different story. More on that below. As of now, Wednesday looks to be a repeat before much cooler air moves in for the end of the week and the weekend. As I type this we are sitting at an astonishing 87 degrees at midnight with a heat index of 93. Wow.

A dangerous bow echo formed in northwest Ohio early yesterday afternoon packing 80 mph winds and hail. Although there was some expectation that it might affect our area last evening leading to the issuance of a severe storm watch for our western suburbs, most of the action occurred well to the west and south of the metro region.

How common is 100 degrees?

Although we will likely fall just short of 100 degrees today, I thought this was a good time to look at 100 degree days in DC. While not extremely unusual, 100 degree days are nevertheless quite rare. If we go back 20 years to the summer of 1985, we have experienced only 26 days of 100 degrees or higher. Interestingly, all 26 of those days occurred in just 8 summers, indicative of heat waves with at least several 100+ days in a lot of those years. For those trying to place a date on their anecdotal recollections, some notable heat waves in the last 20 years when we hit 100 degrees more than once include July 1999, August 1997, July 1993, July 1991, July 1988, and July 1987. Our warmest day in this timespan was August 17, 1997 when the temperature hit 105, only one degree shy of our all-time hottest temperature. Our earliest 100 degree day occurred on June 5th and the latest on September 8th, giving us a 105 day window each year for reaching 100+ over the 20 years. And as only 26 days did so out of 2100 "window" days, this translates to a frequency of just over 1%, making reaching or exceeding 100 a remarkable event.

Pictured at the top right: Lightning over Fairfax on Monday morning, courtesy of Kevin Ambrose.

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