DC heat wave: When temps will peak this weekend

- It's a hard feeling to describe, but there are some mornings you know when you step outside for the first time that you can almost feel the heat coming. Today was certainly one of the mornings. The mid-to-upper 90s with heat index values over 100° are certainly on their way.

With perhaps the worst summer heat wave in a few years on our doorstep, the District of Columbia is under a heat emergency from today through at least next Friday. This means several area pools and splash parks have extended hours, and additional cooling centers are open for those in need. You can find more info here or by dialing 311.

Please take the heat seriously and take proper precautions. Exercise in the early morning or evening hours to avoid the peak heating, drink plenty of water, and above all keep yourself cool be it the air conditioner or the pool.

To help get you through each day, here are some times that you need to know for each day during this heat wave:

While a heat advisory has not yet been issued for the region, one is likely tomorrow with heat index values expected to be around 105° (which is required for a heat advisory in DC). Saturday will likely be the most humid day of the weekend.

11 am: Temperatures likely crack the 90° threshold for the first time. Recommend getting in any morning workout before this time.

2-7 pm: Temperatures likely are at or above 95° during this entire time period. Limit any outdoor activities that will not keep you cool. If the afternoon brings full sunshine, it will feel like 105-110°.

8-9 pm: Temps likely fall back under 90°. Humidity remains high.

Risks to the forecast: There is a very weak piece of energy that will slide across the region tomorrow afternoon which could pop a couple of thunderstorms with the best chance between 3-7 pm, but like Friday, most of the region stays dry. Should this energy fail to cause any storms and afternoon clouds remain limited, 100° is not out of the questioN-- but not favored due to the high dew points. It’s much easier to hit 100° in dry air as opposed to moist air. Record high of 102° from 2011 should remain.

More of a westerly breeze of the mountains and some northwesterly winds aloft lead to some drier air. It’s still humid, but not as much so as Saturday. This being the case, Sunday may avoid heat advisory levels. The drier air will limit storm risks as well, and as of now storm chances are less than 10 percent. The record of 101° from 2010 will probably not be broken.

11 am: Much like Saturday, the majority of the region likely cracks the 90°

2-7 pm: Peak heat time, with highs between 96-99° possible. With humidity a tad lower, it may feel a little “cooler” than Saturday… if you’re able to notice. Peak heat index 98-103°.

8-9 pm: Temps retreat from the 90s around the region, but humidity starts increasing during the evening hours.

Risks to the forecast: A few afternoon clouds would likely be the greatest threat to the forecast, but nothing so major that it would significantly change the forecast. We feel good with our 98° at this time.

Likely the worst day of the heat wave for a number of reasons. DC will have a strong influx of southwesterly winds and “renewed” humidity out ahead of a cold front that will sweep the region later in the afternoon. Likely a mix of clouds and sun, but if we manage more sun than clouds then 100° will be easily reachable. When the front hits the hot, humid air mass later in the day thunderstorms will be possible. Some may be strong to severe.

10-11 am: The morning should start sunny and bright, and temps should quickly soar into the 90s.

1–7 pm: Temps cross the 95° threshold and with enough sunshine would likely cross 100° sometime between 2-4pm. With high humidity, it once again feels like 105-110° and a heat advisory is likely. 

5-9 pm: Best chance for storms to rumble through DC given current weather modeling. Temps quickly fall from the 90s to the 70s in location that do see storms. If DC misses storms, they will likely hang onto the 90s until sunset, between 8-9 pm.

Risks to the forecast: Some of the more recent modeling has been trending drier on Monday. Our forecast high of 98° was made with the anticipation for some clouds, showers, and storms during the second half of the day. If this is not the case, then this day has the best shot at hitting 100° out of the next four days. The record high of 100° which has stood since the blistering heat waves of 1930 may be at risk to be tied or broken.  

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