In a flash, large parts of the Washington region are now officially in a drought, thanks to persistent heat and the sudden onset of dry conditions.
The drought was set up by a simmering summer, the seventh-hottest on record, which turned progressively drier. Although plentiful rains accompanied June and early July, they abruptly shut off thereafter.
September has delivered historically little rain, while temperatures most days (22 of 26) have soared into the summerlike 80s and 90s. Washington’s average temperature has resembled a typical September in Charleston, S.C.
The unusually hot and dry conditions, which work hand in hand, stand to continue for at least another week before our first real taste of fall.
The summer that never ends
So far, Washington has posted its seventh-warmest September on record, and given the forecast, the month could finish around the third- or fourth-warmest.
The temperature has hit at least 90 degrees eight times, more than double the average of three. Up top two additional 90-degree days are possible this month alone. (If we get to nine it would tie for 10th most 90-degree days in the month; and 10 would tie for 7th.)
The frequent 90-degree days fit into a pattern we’ve seen for months now. Through Thursday, the 60 days of 90 degrees or higher is third most on record, trailing only the 67 days in 2010 and 1980. It seems more than likely that this year will end up in third place by itself, although we could still close the gap a bit.
Heat and drought get worse in feedback loop
When it’s hot, the ground dries up faster, which can lead to the rapid onset of drought. And when the ground is dry, it heats up faster, in what can become a vicious, self-reinforcing cycle.
You may have noticed the sound of brown leaves crinkling underfoot and the increasing dryness of grass and plants across the region. Given the speed at which this has occurred, the National Weather Service tweeted that a “flash drought” has unfolded in parts of the region.
“The short-term dryness and heat have quickly overcome the long-term record wetness we’ve seen since April 2018, with impacts from this short-term dryness rapidly increasing,” the agency explained.
As of last week’s update from the federal government’s Drought Monitor, 5 percent of Virginia was under a moderate drought, with D.C. and Maryland at 0 percent. This week, it’s up to 54 percent coverage in Virginia, 92 percent in the District and 33 percent in Maryland.
Jason Otkin, a meteorologist at the University of Wisconsin who published a study on the characteristics of flash droughts, wrote in an email that the D.C. area “is on the northern edge of large region centered on the southern Appalachians” that has seen sudden drought onset due “to a prolonged period of much drier and warmer than normal conditions.”
With no significant rain expected in the immediate future, the drought area seems likely to intensify and expand.
There have been only 0.11 inches of rain this month in Washington. If the city doesn’t build on that tally, September 2019 will finish tied with 2005 for the driest September on record. That total is also one of the lowest of any month on record. October holds that title, when only a trace fell in 1963.
Though there’s no real risk of big rain totals as we close the month, there are a few opportunities for a passing shower or storm. Should the September rainfall total remain below 0.60 inches, it will finish among the 10 driest on record.
Wednesday marked the 13th day in a row with no rain in Washington. That’s the longest stretch this year, though not too uncommon unless it keeps on going.
As recently as last year, there was a 19-day rainless stretch into the first half of July, before the deluges that spurred Washington to its wettest year on record.
Fall is the preferred time for long stretches of dry weather, although they tend to favor October more than September or November. The longest stretch on record with no rain is 34 days, ending Oct. 18, 2007.
More heat to come, but fall-like weather in sight
The good news for fans of cooler, crisper autumn weather? Historically we’re running out of time for intense heat in Washington.
Washington’s current average high is in the mid-70s, and that drops to 70 by Oct. 10. Its latest 90-degree reading on record came Oct. 11, 1919.
It does seem likely that Washington will see a few more 90-degree days into early October — especially around the middle of next week, when an abnormally strong heat dome is forecast to grip the eastern U.S.
The European model even suggests Washington could flirt with its all-time October high of 96 degrees, from 1941, although the model has been above reality with its forecasts more than a few days into the future recently.
Models generally agree that the weather pattern should turn cooler by around Friday of next week, Oct. 4.
By then, it seems, we’re in for a run of highs in the 60s and 70s and lows in the 40s and 50s — much more fitting for the season.
But even as it trends cooler, the chance of meaningful rain seems slim over the next six to 10 days. We may have to wait for the second half of October for a wetter pattern to bring much drought relief.
This article has been updated for the additional 90-degree day that occurred Thursday.