All but two days this July have seen 90-degree temperatures, and we’re likely to add a couple more before the month ends.
The 90-degree milestone is just one of a number of impressive heat records that have been tested or smashed in recent weeks.
90-degree days pile up, and summer has no “chill” at night
The 90-degree days have mounted over the course of three heat waves this month (defined as at least three consecutive days hitting 90 or higher). This first heat wave, which began in late June, lasted 20 days, the second-longest on record. The second heat wave spanned July 17 to 23, while we began yet another Saturday.
The 26 days hitting at least 90 degrees this month top the previous record of 25 from 2011. In addition to being the most 90-degree days in July, the number also exceeds the record count in all Junes and Augusts. The number of 90-degree days during this month alone exceeds 40 percent of entire summers on record.
An unusual number of 90-degree days have also accumulated at other locations in the region. Baltimore is just one day away from matching its July record of 24 such days from 2011, while Dulles needs three more to match its record of 24 from the same year.
Including Washington’s nine 90-degree days in June, there have been 35 such days this year, so far, about 13 more than normal. These 35 days are tied for the fifth most on record year-to-date.
The 90-degree count is just one away from its annual average of 36, using data from 1981 to 2010, with many weeks of summer remaining. The annual average will bump to 40 days next year based on numbers from 1991 to 2020, during which summers have warmed due to climate change and urbanization.
As another indicator of climate change, temperatures have also been persistently warm at night, where a record for duration is in jeopardy.
Tuesday marked the 32nd straight day with lows at or above 70 degrees in Washington. That’s the third-longest streak on record, and it seems we should blow by the standing record of 35 days in 2016 based on the forecast.
Washington’s lowest temperature so far this July of 71 degrees is the warmest minimum temperature of any month on record (assuming a lower temperature does not occur through Friday). The existing warmest monthly minimum temperature is 67 degrees set during July 2011 and August 2016.
Our temperatures have most resembled summer conditions in Dallas and Houston in recent weeks, according to the Southeast Regional Climate Center.
The heat in historical context
There was some time spent discussing how the 20-day heat wave from June 26 to July 15, while very long, was not all that intense. In fact, the average temperature during that heat wave was the lowest among Washington’s historically long events. But after that heat wave ended, the latest rounds of heat are changing the narrative.
When Washington hit at least 96 degrees five days in a row to start last week, the streak tied as the seventh-longest with temperatures that high.
Both Dulles and Baltimore put up six days in a row of 95 or higher. At Dulles, that streak tied for the second-longest on record (since 1963). In Baltimore, it tied for the sixth-longest (since 1872). In Baltimore, all those days were 96 or higher, which is tied for third-longest such streak.
In the past 11 days, Washington has picked up seven days at or above 95 degrees. The annual average is 12. The high of the streak, 99 degrees, is about equivalent to its annual hottest. Baltimore reached 100 on two days.
July to finish among hottest on record during what will probably be a historically hot summer
It’s a near-certainty that July 2020 will finish among the top four hottest Julys on record. Second or third place seems most likely.
Using National Weather Service forecast numbers for the rest of the month, a projection of 84 degrees for the average temperature ties this July with 2012 as second-hottest. July 2011 is the record-holder, with 84.5 degrees.
By the time this month is over, the four hottest Julys on record will have occurred since 2010.
This month should also finish safely above the hottest August on record, and no Junes have been close. In other words, July 2020 will probably be Washington’s second- or third-hottest month ever observed.
For the summer overall, Washington’s average temperature is running fourth-warmest on record. Unless August offers an unusually cool surprise, it seems probable that this summer will rank among the top 10 hottest, the seventh such instance since 2010.
Jason Samenow contributed to this report.