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D.C.-area forecast: New heat wave begins today, and the humidity will become oppressive by Sunday

“Lily along Connecticut” Avenue on June 15. (Edward Wood <span style="text-decoration: underline;"><a href="">via Flickr</a></span> )
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A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.

4/10: Bearing in mind it may be the most “comfortable” heat of the next week, let’s leave room to subtract as heat and humidity turn oppressive by Sunday/Monday.


Today: Mostly sunny. Not too humid — yet. Highs: 90-95.
Tonight: A few clouds. Muggier. Lows: Near 70 to mid-70s.
Saturday: More sun than clouds. Steamy. Highs: Low to mid-90s.
Sunday: Oppressive heat index values. Highs: Mid- to upper 90s.

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The longest and hottest heat wave of the summer begins today and your body will not be happy. With little chance of cooling afternoon storms, please mindfully seek shade, replenish your sweat with water and electrolytes, and wear light-colored, lightweight, breathable clothing. The humidity isn’t awful but will build through Sunday and early next week, resulting in heat indexes of 100 to 105, near-dangerous levels.

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Today (Friday): High temperatures for the start of our heat wave eye the 90- to 95-degree range. With merely subtropical dew points in the 60s, heat index values shouldn’t exceed the mid-90s. Just a few clouds would be nice in this instance but sunshine looks to dominate. If you’re lucky, you’ll feel a quick northwesterly breeze around 5 mph — for a moment. Confidence: High

Tonight: A few, periodic clouds are possible, and haze may start to slowly become visible as that humid feeling slowly increases. That’s more water vapor moving in. Temperatures settling around 70 outside the Beltway, to perhaps mid-70s downtown, are about the best we can dip to, for pre-dawn low temperatures. Winds quickly drop from very light to nearly calm after sunset. Confidence: Medium-High

Follow us on Facebook, Twitter and Instagram for the latest updates. For related traffic news, check out Dr. Gridlock. Keep reading for the forecast through into next week.

Tomorrow (Saturday): Sunshine continues to dominate over any periodic (merciful?) clouds. It feels a half-notch warmer thanks to dew points heading too close to the tropical 70-degree mark. High temperatures may add a couple degrees but stay roughly in the low- to mid-90s. The heat index could top out around 100 degrees. Very light south-southwesterly breezes may not offer much refreshment. Confidence: High

Tomorrow night: A few clouds may bubble up again, helping to buoy temperatures (unfortunately) like an insulating blanket in the atmosphere. Low to mid-70s are as low as we get, and thanks to fairly tropical dew points around 70 degrees, the air conditioning may need to stay on most of the night. Confidence: Medium-High


Sunday: Heat index values around 105 degrees are possible, so please be careful. Oppressive mugginess and heat look probable, with high temperatures in the mid- to upper 90s possible. Still-sunny skies with little to no prospect for cooling afternoon thundershowers means: oof! Confidence: Medium-High

Sunday night: More clear skies than not, albeit with a little haze. The entire region hovers in the muggy 70s again by just before dawn (maybe even only near 80 downtown) — and it will take the entire night to get that “cool” so you may want to keep the air conditioning on all night. Hang in there! Confidence: Medium-High

Oppressiveness continues with heat index values in the 100-105 range likely Monday and Tuesday. Perhaps reaching just a bit, there is a slight signal that we see a few more clouds and perhaps a passing (cooling!) thundershower later, both days. Fingers crossed. Low 90s with a heat index around 100 possible with a few clouds and showers. Mid-90s with a heat index around 105 more likely if it stays rain-free and sunny. Confidence: Medium