Midnight Update: After dropping to 90°, the temperature is back up to 91° at midnight; the temperature has now been at 90° or higher for 13 consecutive hours.
8 PM Update: The high has actually popped up to 98° after 5:00.
6 PM Update: The preliminary high/low of 97°/77° came in 1° below forecast, but the predicted 102° tomorrow and continued 90s into next week still give a chance of at least tying the July temperature record. (As of 6 pm, it's been 97° for 3 consecutive hours; hard to believe it couldn't make it to 98° at some point.)
With a high so far today of 97°, this is now the 10th consecutive day of 90° temperatures or higher in Washington, the second time this has occurred in the summer of 2010. The even hotter readings expected tomorrow will undoubtedly tie the 11 day stretch of 90°+ in June.
How do these current year heat waves compare with those of the past? Since temperature records began at or near the current location of National Airport in 1929, there have been 12 periods of 12 or more consecutive days with 90° temperatures or higher. The record, by far, was set by the 21 days ending August 14, 1980. That heat wave began with only a 2-day break following the 9-day streak ending on July 22. Ten days following the record streak, another 14-day streak extended from the last week of August through September 6. In all, there were a record 67 days of 90°+ temperatures in 1980, which also holds the current record for the hottest summer. The earliest 90° reading that year was May 13, and the latest was September 23.
The second and third place holders for heat wave length in the modern era are 1999 (18 days) and 1988 (17 days).
Temperatures are expected to moderate somewhat by early next week, but forecast highs of 90° or warmer through at least next Thursday could bring the current streak to 16, which would tie the 4th place record set on July 18, 1993.
Image (click to enlarge): Washington, DC longest streak of consecutive 90° days per year; CapitalClimate chart from National Weather Service data, background photo from Kevin Ambrose
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