The Washington PostDemocracy Dies in Darkness

Washington posts warmest October in nine years and driest in 16 years

Mount Vernon trail, Oct. 21, 2016 ( <a href="https://www.flickr.com/photos/52478527@N00/30179203770/in/pool-capitalweather/">Erinn Shirley via Flickr</a> )
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October was stellar for those who appreciate unseasonably warm days and little rain to disrupt outdoor plans. But for those who prefer cooler, crisp autumn weather and the occasional soaking rain to green up local flora, the month was a downer.

Over half of October featured high temperatures in the 70s and 80s and, for the fifth straight month, ended up warmer than normal.  It ranked as the 10th warmest October on record and was the warmest October in nine years.

The average temperature during the month was 63.1 degrees, 3.6 degrees warmer than normal. It was heavily influenced by five-day stretch (Oct. 17-21) in the middle of the month when temperatures averaged 15 degrees above normal and it felt more like late August.

Warm weather often begets dry weather and D.C. recorded only 0.9 inches of rain during the month, 2.5 inches below normal. It ranked as the 36th driest October since records commenced in 1871, and was the driest October since 2000.

The last calendar month to have less rain than this October was November 2012’s 0.6 inches.

D.C. only managed around a quarter of an inch of rain on its wettest day and parts of the area slipped into the abnormally dry category in the U.S. Drought Monitor. A small pocket of eastern Loudoun County was even classified in moderate drought.

Warm weather extremes were certainly more prevalent than cold extremes. Here is the list of all the records set in D.C., Dulles and Baltimore during the month:

D.C.

  • Oct. 19: Record warm low temperature of 65 tied 2013.
  • Oct. 20: Record warm low temperature of 68 bests 64 from 1885.

Dulles

  • Oct. 17: Record high of 84 breaks record of 83 from 1963.
  • Oct. 18: Record high of 85 breaks record of 82 from 2007 and 1963.
  • Oct. 19: Record high of 87 breaks record of 83 from 1991 and 1963.
  • Oct. 20: Record high of 83 ties record from 1969.
  • Oct. 20: Record warm low temperature of 65 bests 59 from 1993.
  • Oct. 30: Record high of 84 breaks record of 81 from 1996.

BWI

  • Oct. 18: Record high of 84 breaks record of 82 from 1945, 1928 and 1908
  • Oct. 19: Record high of 87 breaks record of 82 from 1947 and 1908.
  • Oct. 20: Record warm low temperature of 65 ties 1910.
  • Oct. 30: Record high of 83 ties record from 1946.

Prevailing pattern

A dip in the jet stream over the Pacific Northwest this past month resulted in frequent warm high pressure ridging over the Midwest, East and South.  This supported yet another warm autumn month.

Year-to-date

Thanks to the warm and dry October, 2016 is now tracking warmer (third warmest) and drier (fourth driest) compared to most years this century.  We have a shot to edge cooler to colder later in November and especially December,  but La Niña tends to favor drier weather, so the precipitation rank may not change or could even worsen a bit to round out 2016.

After a super-warm start, November could turn much colder by Thanksgiving

October forecast review

How’d we do?

The temperature forecast

I wrote: “… projecting a warmer-than-normal month with temperatures running one to three degrees above normal.”

Reality: The direction of the temperature anomaly was 100 percent correct, but the actual departure from normal is coming in just outside the range (about 3.6 degrees above normal vs. the range of 1 to 3 degrees projected).

The rain forecast

I wrote: ” … favor near-normal rainfall between 3.0 to 3.8 inches”

Reality: This was far too optimistic. October only got about one-third of this projection with 0.9 inches.

Summary review

Temperature direction (warm) was accurate again, but not quite warm enough, while near normal precipitation expectations were a bust (below normal instead).

Grade: B-

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