Brutal heat from Phoenix to Boston triggers alerts for 100 million
The heat and humidity may lighten up a bit on Friday before rising back over the weekend to the most extreme levels of the summer.
DC Mayor Muriel E. Bowser (D) has declared a heat emergency until Mondayopen shelters and cooling centers.
In such oppressively hot and humid conditions, people spending time outdoors are advised to hydrate and take frequent breaks. It is also an important time to check vulnerable groups.
People most at risk of heat-related illness include older adults – especially those who are socially isolated or ill – outdoor workers, the very young and anyone without access to air conditioning. Heat is the top weather-related killer in the United States.
Before this week’s four straight 90-degree days, the District had only strung together streaks of two consecutive 90-degree days this summer. Highs are forecast to reach at least the mid-90s through Sunday before dropping.
Friday will probably not be quite as steamy as Thursday. Still, high temperatures should approach 95 degrees.
The sweltering conditions peak into the weekend, with highs in the upper 90s to possibly 100 degrees. Computer models generally simulate the highest temperatures and highest chance of reaching 100 on Sunday.
The National Weather Service will likely issue heat advisories over the weekend. There’s an outside chance it will issue an excessive heat warning Sunday, reserved for cases when the heat index is forecast to reach at least 110 degrees.
Low temperatures will also be unseasonably warm — only dropping to near 80 in the city Saturday and Sunday night, with lows in the 70s elsewhere.
Here are the projected high temperatures and maximum heat index values for Friday through Monday:
- Friday: 95, maximum heat index 98
- Saturday: 98, maximum heat index 105
- Sunday: 99, maximum heat index 107
- Monday: 93, maximum heat index 102
These temperatures – coinciding with some of the historically hottest days of the summer – will probably fall short of most records, but are still as much as 10 degrees above normal.
Washington Dulles International Airport’s record high of 99 on Sunday has a chance to fall, but Reagan National Airport’s and Baltimore-Washington International Marshall Airport’s records of 102 are likely safe.
The excessive heat is associated with a diffuse high-pressure zone, or heat dome, over the southwestern United States that bends eastward. On Thursday, this heat dome triggered heat alerts for 100 million people from Phoenix to Boston.
A story of 100-degree heat in Washington
Washington hasn’t reached 100 degrees since Aug. 15, 2016. That year, there were four days at or above 100, including three in a row in August.
The district reached 99 once this year — which is right around the city’s average annual maximum temperature in the historical record.
Since 1872, Washington has posted 121 days at or above 100 — and averages a little less than once a year. The warmest days reached 106 in July 1930 and August 1918.
Of these 121 recorded 100-degree days, 66 have occurred in July, 33 in August, 18 in June and four in September.
These 100-degree days tend to come in bunches. 2016 had four, 2012 eight, 2011 five and 2010 four. 1930 produced 11, the most in a single year.
Interestingly, the nearly six years (or 2,165 days) since the last 100-degree day in Washington are among the longest streaks on record:
While National has seen this prolonged 100-degree day drought, other places in the area have not. Dulles last reached 100 on August 12, 2021. BWI’s last 100-degree day came on July 20, 2020. It’s likely that National’s proximity to the relatively cooler waters of the Potomac River has kept temperatures down during recent heat waves.
The days when Washington reaches 100 degrees share certain temperature markers during the day. It usually reaches 95 degrees by noon and stays at least that hot until 6 p.m. 18.00 – a dangerous interval of extreme temperatures.