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Posted at 03:15 PM ET, 08/02/2011

Will August be as hot as July in Washington, D.C.?


NOAA’s Climate Prediction Center says flip a coin as to whether it will be warmer or cooler than average in the D.C. metro region during August, while the heat dome holds firm in the South.
After a record hot July, should Washingtonians be dreading what’s to come in August?

The good news is that August is usually cooler than July. The average temperature in July is 79.8 compared to 78.1 in August. But this difference is quite small and it can still be scorching.

Take, for example, August 1980 which set monthly records for both average temperature (82.8 degrees) and the number of 90+ degree days (22). That made August of 80 only slightly less sweltering than July 2011, with an average temp of 84.5 and 25 90+ days.

Is there a correlation between a hot July and hot August? The blog Capital Climate provides some insight:

Although there is little month-to-month correlation in Washington temperatures, the July-August correlation is one of the strongest in the year. The correlation coefficient of 0.227 says that about 23% of the variance in August temperature is explained by July’s temperature.

It adds that that 10 of the top 11 hottest Julys have had warmer than average Augusts.

On the other hand, the National Weather Service Forecast Office in Sterling pointed to several examples of the pattern switching from hot in July to relatively cool in August:

LAST SUMMER I DID A TEMP COMPARISON OF 5 OF THE HOTTEST SUMMERS ON DC RECORDS - 1930..1936..1980..1988.. AND 2010 . . . .IN THE 1ST 4 OF THOSE THERE WAS A SIGNIFICANT COOL DOWN DURING MID AUGUST. THE EXCEPTION WAS LAST SUMMER WHICH KEPT UP W/ THE >90 TEMPS THRU THE END OF AUG. . . . IN 1930 THE HIGH HEAT KEPT UP THRU 8/9...TOPPING 100 ON 5 MORE DAYS. BUT THEN TEMPS DROPPED DRAMATICALLY - AFTER A HIGH OF 102 ON 8/9 THERE WAS A LOW OF 56 ON THE 12TH AND 55 ON THE 13TH. BOTH THE 8/9 HIGH AND 8/13 LOW REMAIN AS RECORDS FOR THE DAY. THAT MUST`VE BEEN ONE HECK OF COLD FRONT.

What about this year?

NOAA’s Climate Prediction Center gives equal chances of above or below normal temperatures - so not much help there.

I asked Matt Ross - CWG’s seasonal outlook author (who predicted a slightly hotter-than-average August back in May) - for his latest thoughts: “There is nothing at this time that suggests that we won’t have another warmer than normal month.  August would make seven consecutive above normal summer months at Reagan National Airport.”

CWG forecaster David Streit - who specializes in long-range prediction at the Commodity Weather Group - also expectd above normal temperatures through the entire month, but noted a dip in the jet stream (or trough) forming near the Hudson Bay that may occasionally dip south, suppressing the massive heat dome that has brought all the misery over our region and to the southwest.

“These features are going to do battle,” he said.

Synthesizing all of the above, I’ll conclude that odds are good August will be hotter than average - especially given the blistering start. But there’s no strong signal - mercifully - for record heat to rival 1980.

By  |  03:15 PM ET, 08/02/2011

Categories:  Latest, Extreme Heat, Local Climate

 
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