D.C.’s longest, hottest heat wave has waited for September

Compared to recent years, the summer of 2014 has delighted Washingtonians. Until this week.

Sunday hit 96, Labor Day soared to 95, and we’re headed towards the mid-90s again today.

This summer, the only comparably hot stretch occurred on the first three days of July when it was 93, 99, and 92.

At noon today, D.C. was the hottest location in the nation on The Weather Channel’s map, with a temperature of 92.

(Weather.com)

Noon temperatures ET (Weather.com)

(Other recent instances of D.C. being hottest: June 18, 2014July 16, 2013 | July 17, 2012 | June 20, 2012 | July 22, 2011)

Some minor relief is possible for the second half of the work week, as humidity drops some and high temperatures are closer to 90. But if we manage to hit 90 Wednesday, we’ll have achieved our longest streak of days at or above 90 all summer.

GFS model forecast highs through Saturday outlined in red.

GFS model forecast highs through Saturday outlined in red.

There’s a chance we’ll reach 90 Thursday, Friday, and Saturday as well, and could run the streak of 90+ days to seven. A strong cold front moving through Saturday night assures us any such streak will then end.

Our tally of 90-degree days in 2014 through today stands at 20, which is about 13 below than 1981-2010 average year-to-date. In September, we average 3 90+ days. We’ll have little trouble topping or at least meeting that this year.

As hot as this period promises to be, none of the individual days should be record-setting.  Record highs in early September are mostly in the upper 90s to around 100 or so.

Why such heat so late in the season? For significant stretches of the summer, the jet stream has dipped over the East Coast, favoring cool winds from the north and northwest.

But since the weekend, we’ve had a bump or ridge in the jet stream over the East, which has facilitated flow from the steamier south and west directions.

High altitude flow pattern from GFS model is a warm one for the Mid-Atlantic and Southeast through Saturday.  Orange and red areas approximate warmer than normal temperatures.  Blue and green areas approximate cool air.  (WeatherBell.com)

High altitude flow pattern from GFS model is a warm one for the Mid-Atlantic and Southeast through Saturday. Orange and red areas approximate warmer than normal temperatures. Blue and green areas approximate cool air. (WeatherBell.com)

As shown in the map above, this jet stream pattern will hold through Saturday. On Sunday, it collapses.

What we’re experiencing this week is a very common mid-summer flow pattern which we – very fortunately – avoided during the thick of July and August.

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