Unusual April Weather Continues

NOAA's Precipitation Outlook for May 2018

This month has largely featured at or below normal temperatures, with the exception of the three-day period of April 12-14 when D.C.’s high temperatures ranged from 78° to 86° (more like June).  Washington, D.C. will also see some beneficial rainfall this afternoon and tonight with a slow moving area of low pressure.  That’s good news for springtime allergy sufferers and it will also help offset D.C.’s drier than average conditions.

Average monthly temperatures (including daily high and low temperatures are 2° below average) in the Nation’s Capital through April 23.  DC’s high and low temperature of 49°/40°, respectively, on April 17 produced a daily mean temperature of 44.5°.  That was D.C.’s coolest day to occur in the second half of April since April 16, 2014 (that had a daily mean temperature of 42.5°).  Temperatures are not expected to deviate from average significantly enough over the last few days of the month to prevent April from finishing with cooler than average temperatures overall.  That would make April 2018 D.C.’s first cooler than average April since 2007.

With rainfall totals of approximately an inch likely through tomorrow for the immediate DC Metro Area, Washingtonians could also finish April with a near average amount of monthly rainfall (3.06”).  The Nation’s Capital has had 2.09” of April rain through yesterday.  This month could also become D.C.’s first wetter than average April since 2015.  Although that isn’t a very long period of time, having an even slightly wetter than average month is important given the ongoing rainfall deficit in Washington, D.C.

Washington, D.C. had below average monthly rainfall in all but seven months during the 32-month period from August 2015 through March 2018.  That produced a rainfall deficit of 16.42” in the Nation’s Capital during that time.  There have been eight drier than average months in Washington, D.C. just since April 1, 2017.  This February’s rainfall surplus of 2.17” did help reduce the swath of the drought conditions across the Mid-Atlantic Region.  However, the April 19 Drought Monitor Index showed a large amount of the DC-Baltimore corridor is experiencing “abnormally dry” conditions.  Much of the District of Columbia is also experiencing “moderate” drought conditions.

That’s why the rain this afternoon and tonight is so beneficial.  Washington, D.C.’s rainfall deficit from January 1, 2018 through March 31 is only 1.26”.  That helps illustrate just how dry January and March were in D.C. given February’s rainfall surplus (2.17”).  With the growing season underway, it would be great heading into the month of May with near average annual rainfall.  NOAA’s outlook for May is for an increased probability of above average rainfall in the Mid-Atlantic Region.