This heat wave is likely to be the most intense of this summer (so far), exceeding last week’s event, when the District hit 97 degrees on consecutive days.
Temperatures are forecast to trend upward through Friday, with highs into the mid-90s on Wednesday and mid- to upper 90s on Thursday.
Confidence in the prospect of temperatures soaring to around 100 is highest Friday and Saturday, when both the European and GFS models are predicting such extreme heat. Sunday is likely to be very hot, too, but by Monday models don’t agree on the intensity of the heat.
Here is a breakdown of what each model is predicting through Monday:
- Wednesday: 94
- Thursday: 98
- Friday: 98
- Saturday: 99
- Sunday: 101
- Monday 93
- Wednesday: 95
- Thursday: 97
- Friday: 102
- Saturday: 100
- Sunday: 100
- Monday: 99
Of course, it’s not just the heat. Dew points, an indicator of humidity, are forecast to be near 70 on Friday and Saturday, and perhaps into the low to mid-70s Sunday and Monday. Such a combination of heat and humidity is likely to make the air feel like 105 to 110 degrees during this stretch.
The National Weather Service is predicting maximum heat index values of 106, 105 and 105 Friday through Sunday.
Overnight temperatures are likely to be unusually warm, perhaps record-challenging, dropping only to around 80 degrees downtown.
Given the intensity of the expected heat, heat advisories by the National Weather Service and a heat emergency declaration by the District are likely.
Some uncertainty in how hot and where
While our most reliable models uniformly predict scorching heat Friday, forecast uncertainty in just how hot it gets will increase over the weekend into early next week. That’s because a weak cool front will lurk to the north. If it settles a little farther south than forecast, the potential for excessive heat will be short-lived.
This cool front may also serve as a corridor for afternoon thunderstorms, which could ease the heat’s intensity.
The highest confidence for an extended period of triple-digit heat is south of Washington, toward Fredericksburg.
North of Montgomery County and toward Baltimore, the heat won’t be quite as intense or long-lasting.
For example, even Friday, the GFS model is forecasting a high of around 100 inside the Beltway but low to mid-90s in northern Maryland.
The heat is forecast to form as a massive heat dome parked over the central United States early this week bulges eastward.
Over the weekend, it will retreat some, but a hot flow of air will continue over the Mid-Atlantic because of a high-pressure system to the southeast, whose clockwise flow will continue to circulate steamy air northwestward.
There are indications that during the early to middle part of next week, a strong cold front will push through the region, resulting in a stretch of normal to below-normal temperatures during July’s final week.