Brutal heat from Phoenix to Boston triggers warnings for 100m
The heat and humidity could ease somewhat on Friday before returning to the summer’s most extreme levels over the weekend.
DC Mayor Muriel E. Bowser (D) has declared a heat emergency by MondayOpening of shelters and cooling centers.
In such sweltering hot and humid conditions, people who are outdoors are advised to stay hydrated and take frequent breaks. It’s also an important time to review vulnerable groups.
Among the people most vulnerable to heat-related illnesses are older adults — especially those who are socially isolated or ill — outdoor workers, the very young and anyone who doesn’t have access to air conditioning. Heat is the weather-related killer in the United States.
Prior to this week’s four consecutive 90-degree days, the district had only strung together streaks of two consecutive 90-degree days this summer. The highs are predicted to be at least in the mid 90’s by Sunday before trending lower.
Friday will probably not be quite as hot as Thursday. Still, high temperatures should be close to 95.
Muggy conditions will peak over the weekend with highs in the upper 90’s to possibly 100 degrees. Computer models generally simulate the highest temperatures and highest chance of hitting 100 on Sunday.
The national weather service is expected to issue heat warnings over the weekend. There is a possibility that an excessive heat warning will be issued on Sunday, reserved for cases where the heat index is expected to reach at least 110 degrees.
Low temperatures will also be unusually warm – only dropping to nearly 80s in the city on Saturday and Sunday night, with 70s elsewhere.
Here are the predicted high temperatures and maximum heat index values from 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
Those temperatures – which coincide with some of the summer’s historically hottest days – are likely to fall short of most records but are still up to 10 degrees above normal.
Sunday’s Washington Dulles International Airport record high of 99 has a chance of falling, but Reagan National Airport and Baltimore-Washington International Marshall Airport’s records of 102 are likely safe.
The excessive heat is associated with an extensive high-pressure zone, or heat dome, bending eastward over the US Southwest. On Thursday, that heat dome triggered heat warnings for 100 million people from Phoenix to Boston.
A history of 100 degree heat in Washington
Washington has not reached 100 degrees since August 15, 2016. This year there have been four days at or above 100, including three in a row in August.
The district reached 99 at one point this year — roughly the city’s average annual maximum temperature on the historical record.
Since 1872, Washington has reported 121 days at or above 100 — hitting the mark a little less than once a year on average. The hottest of those days reached 106 in July 1930 and August 1918.
Of these 121 recorded 100 degree days, 66 occurred in July, 33 in August, 18 in June and four in September.
These 100 degree days tend to come in bunches. There were four in 2016, eight in 2012, five in 2011 and four in 2010. 1930 produced 11, the most in a single year.
Interestingly, the nearly six years (or 2,165 days) that have passed since the last 100-degree day in Washington is among the longest streaks on record:
While National has experienced this sustained 100-degree daily drought, other places in the region have not. Dulles last hit 100 on August 12, 2021. The BWI’s most recent 100-degree day came on July 20, 2020. It’s likely that National’s proximity to the relatively cooler waters of the Potomac River held back temperatures during the recent heatwaves .
The days when Washington hits 100 degrees share certain temperature markers throughout the day. It usually reaches 95 degrees by noon and stays at least that hot until 6 p.m. — a dangerous interval of extreme temperatures.