From the ABC 7 Weather team

Summer arrives with an impressive heat wave

June 17, 2012 - 05:58 PM
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June is off to a rather cool start so far but the thermostat will be cranking by midweek! While we’ve already had one heat wave (defined as three days at or above 90 degrees) this next one will be a notch higher.

The average monthly temperature so far in June is a half degree below average at 72.8 degrees! This is a far cry from last June when highs were a whopping 4 degrees above average! Things will change as we slide into summer this week, so don’t get too used to the comfortable temperatures.

What typically causes East Coast heat waves to develop is a sprawling high pressure ridge that moves in at the surface and aloft. This deflects the jet stream well north into Canada. Surface high pressure positioned off the East Coast allows south to southwest winds to be directed up the Interstate 95 corridor. The ridging also suppresses cloud cover, allowing the mercury to rise and the heat index to be unrelenting.

This scenario will pan out by midweek. A few impulses in the upper atmosphere; one in the Midwest weakening as it heads for the East Coast Monday and another in the Northern Plains will eventually move into Canada. As this happens, warm air will filter in from the south Wednesday. The heat will remain Thursday but get bumped down just a notch as a very weak cold front tries to move in from the north.


What all this boils down to is a stretch with temperatures at or above 90 degrees, beginning on Wednesday. As a matter of fact, Wednesday (the first official day of astronomical summer) and Thursday look to be the hottest with near record high temperatures.

Here are the records that could be tied or exceeded:
Wednesday, June 20th… 97 degrees at Dulles International and 99 degrees at Reagan National.
Thursday, June 21st…. 98 degrees at both Reagan National Airport and Dulles International

The heat combined with dew points in the lower 70s will yield heat indices between 100 and 110 degrees with heat related advisories quite possible for Wednesday and Thursday. Remember to wear light-colored clothing, avoid exercising or outdoor labor if at all possible during the warmest part of the day, 10 a.m. to 4 p.m. and drink plenty of water. Also, check on the elderly, make sure pets stay inside as often as possible and never leave your child in the car.


So far, there have been 5 days at or above 90 degrees at Reagan National this year and 3 so far this month. In a typical summer there are 25 of these hot days. If you remember not too long ago in the summer of 2010 there was 57 days’ worth of 90 degree heat, which tied for the most in a given summer and was 12 days off the record for an entire year.

While temperatures will “cool down” a bit following the Wednesday-Thursday heat episode, highs will still flirt with the 90 degree mark through the weekend.

Stay cool and be sure to tune into WTOP Radio and ABC7 News for the latest forecasts and any heat-related advisories that may be issued for Wednesday and Thursday.

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