The meteorological spring March-May period easily scored as the warmest on record in Washington, D.C., beating 1977 and the close follow-up 2010 by about 1.5 degrees F. Now, two of the top three warmest springs in 141 years of records have occurred in the last three years.
The warm spring pattern persisted through May with the monthly average temperature end up about 5.4 degrees warmer than normal, third warmest on record.
May Average Temperatures at 71.4F (+5.4F)
March-May Average Temperature at 62.2F (+5.7F)
The top three warmest Mays have occurred since 1990, but 60% of the years on the top ten list are still before 1960.
One record high was set during May the area: on May 28 Dulles hit 90, tying the record from 1991. We saw a handful of record high minimum temperatures set at Dulles and one at Reagan National.
At Reagan National, 58% of the days saw highs in the 80s or higher. Only 32% saw lows below 60-degrees.
Here are the contributions from each month to this new record:
Precipitation started catching up in May from a very dry spring status, but it was not enough to stop 2012 from becoming the 10th driest spring on record (May by itself was 66th driest).
May Average Precipitation at 3.12” (-0.89”)
March-May Average Precipitation at 6.16” (-4.37”)
As many of you know, May was a very random month in terms of regional precipitation patterns. Areas west and south of DC seemed to do better than north and east. Baltimore was the laggard with just under 2”, while Dulles and surrounding areas was the swampy area. This should translate into a lot more Virginian mosquitos in the next few weeks!
Prevailing weather pattern: persistence wins
The amazing thing about May is that the jet stream pattern was nearly exactly the same as the majority of the prior 11 months with warm-to-hot ridging in the eastern 2/3 of the U.S. and cool troughing toward the Pacific Northwest. This pattern is thought to be a remnant of the La Nina pattern of the past two years. We may see changes to this prevailing jet stream pattern later this summer when an El Nino tries to take shape.
As noted yesterday afternoon, the first 1/3 of June is expected to arrive cooler than normal due to a nice cool, early summer trough over the Eastern U.S. By around mid-month, we could see a return to hotter weather, but for now it looks like we’ll be taking an extended break from the 90+ temperatures that hit our area earlier this week. When the hotter weather returns, it is not clear how long it sticks around (it may be another series of brief events again).
The National Weather Service once again paints D.C. with EC for both temperature and precipitation throughout our area. EC means Equal Chances of below, normal, or above normal temperatures (33.3 chance each).
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):
You can click on your closest airport location here:
Historical Washington, DC data provided by Speedwell Weather and NOAA. See also: Ian’s excellent rundown on May climatology