With more heat on the way, a historic August is likely in DC

- There is little doubt that Monday’s weather, followed but Tuesday afternoon’s, is some of the nicest we have experienced over the past couple of months in the DC area. We in the weather department have stressed that you get out and enjoy it, because unfortunately it will not last.

Indeed, it now appears as though the DC region will be heading for yet another heat wave, starting as early as Thursday. Now, the technical definition of a heat wave is simply three or more days in a row at or above 90°.

By that definition, let us review our heat waves since the start of meteorological summer (June 1) in the District:

#1: June 19-21: 3 days above 90°

#2: July 5-9: 5 days above 90°

#3: July 13-19: 7 days above 90°

#4: July 21-August 2: 13 days above 90°, 1 day above 100°

#5: August 6-8: 3 days above 90°

#6: August 10-24: 12 Days Above 90°, 3 days above 100°

That’s right. By the technical definition of a heat wave, we will be in the midst of heat wave number 7 by the end of this week.  Computer model guidance as of Tuesday morning was suggesting it could be a longer-lived heat wave as well, suggesting a 6-10 day stretch of 90° days to close out the month of August. Whether or not the stretch actually happens will be heavily dependent on whether or not clouds or thunderstorms can put a stop to daytime heating in the early afternoon, but as of Tuesday morning, the argument for another long stretch of heat is valid.

Of course, some will brush this off as a case of “hey, it’s DC in the summertime, heat waves happen.” While true, we are now in late August and by this time of year, long stretches of hot days are not nearly as common. Meteorological autumn does start next Thursday, after all. The region has also already lost over an hour a day of sunlight, and therefore daytime heating, and continues to lose over 2 minutes per day at this point.

While a hot second half of summer was forecasted by the weather team, the intensity and longevity of the heat waves has been the surprise of the summer, particularly so far through August. This is true to the point that the coming stretch of 90° weather just may push this August in DC into record territory.

Here are five numbers to know to put the extreme summer heat into perspective:

#1: 17 & 3
The number of 90° and 100° days Washington, DC has seen so far in August, respectively. To toot our own horn very quickly, DC has now seen 45 days above 90° this summer. This is nearly perfect with our summer call of 45-55 days. Even though we expected July and August to be the hottest months, we would be lying if we said we were not impressed by the month we’ve had. If August ended today, 17 days would still be a top 10 August in DC as far as number of 90° days is concerned. These numbers are even more impressive considering DC only averages ten 90° days in the month of August, and saw three 100° days in a month that typically averages none.

#2: 22
The record for most days above 90° in the month of August in Washington, DC. Records of daily DC temperatures go all the way to 1872. This record was set during 1980, consequently the hottest August in one of the hottest summers that DC (and the United States) has seen in recorded history. With eight days remaining in the month of August and another heat wave likely beginning on Thursday, it is not at all unreasonable to suggest that this record may fall.

Only 4 Augusts in Washington, DC history have seen more than 20 days of the month with high temperatures above 90°. It’s been 26 years since this last happened, back in August of 1988. Other than that, only 1983, 1980, and 1943 have surpassed the 20-day mark going all the way back to 1972. So it’s a very elite group 2016 will likely be entering as early as the end of the weekend.

#3: 40
The number of days above 90° in Washington, DC in just July (23) and August (17) so far. The record for the highest two month total is only 43 from both 1980 and 1988. Given that the final 8 days of the month currently look mostly, if not all above 90° for afternoon high temperatures, this is another record that will likely belong to 2016 before the month is out.

This number is even more impressive given the slow start to the summer. May, which typically averages a couple 90° days, failed to register any and June, which averages 7, only saw 5. There is little doubt that the second half of summer has more than made up for cool first half.

#4: 83.3°
The current average temperature for the month of August in Washington, DC as of August 23. With just over a week remaining in the month, this puts August of 2016 in first place for the hottest August of all time in the DC region, leading August of 1980 by half a degree (82.8°).

If Tuesday morning’s run of the European model is absolutely correct (it likely is not…) then the month will close with an average temperature 82.4°, missing the record but coming in above 1995’s average temperature of 81.3 for second place. To summarize, there is a chance that if you are below the age of 36, you are living through the hottest DC August of your lifetime so far.

#5: 5
One hand, that is all you need to count the number of days, including today (August 23), where the low temperature in Washington, DC fell below 70° in July and August so far. Sometimes to get a true sense of how back a summer in a city is, you need not look at the high temperatures but instead the low temperatures. The District’s inability to cool off at night the second half of summer has certainly been a story. Tuesday morning in DC (67°) was the coolest since July 3 (64°).

To put into perspective just how staggering this is, the average number of mornings that DC usually spends in the 60s in July and August is 24. The two seen in July were second only to 2012 for the fewest on record, and the 3 so far in August currently has it tied with 1978 for the fewest. Combined, the two months hold a 4-day lead on 2012 for the fewest of all time with 8 days to go. Yet another record the region does not want, but just might break before the books close on August next Wednesday.


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