How unusual is this cool weather in Washington, D.C.?

It’s mid-afternoon in mid-August and, under full sunshine, Washington, D.C. is just 77 degrees.  The average high for August 14 is 87.

Today currently ranks as tied for the 4th coolest August 14 on record dating back to 1929.

This morning’s low of 62 degrees ranks as the 11th coolest since 1929, seven degrees below normal.  The last time it was this cool in August was August 31, 2009 notes CWG’s Rick Grow.

“Prior to August 2009, you’d have to go all the way back to Aug 13, 2006 to find a colder low (61) [at DCA],” Grow says. “Today, tomorrow and Friday are on track to be the coldest three consecutive August mornings since 2004, which featured lows of 62 (6th), 58 (7th), and 59 (8th).”

Thursday morning's low temperatures forecast by the high resolution NAM model. (WeatherBell.com)

Thursday morning’s low temperatures forecast by the high resolution NAM model.  Notice the 40s in the mountains to our west (WeatherBell.com).

According to the Southeast Regional Climate Center, today’s weather in Washington, D.C. is most similar to Portland, Maine on average at this time of year.

Or, another way to look at it, today’s weather is very similar to the averages in late September or late May locally.

We’ll have more of this fine late spring or early autumn-like weather through Friday as we remain under a big dip in the jet stream, allowing Canadian air to stream southward.

Evolution of jet stream over next 5 days (WeatherBell.com)

Evolution of jet stream over next 5 days (WeatherBell.com)

By early next week, the jet stream will flatten out, allowing a return of warmer but, most noticeably, more humid air.

Although we’ve been in a cool stretch since late July ( temperatures similar to long-term averages in New York City), our average temperature over the last twelve months is 1.6 degrees above average and most similar to long-term averages in Raleigh, North Carolina.

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