Nearing May’s Halfway Point

A Warm Up Looms for much of the Eastern U.S.  (Source: NOAA)

As May’s midway point approaches, it’s a good time to gauge where weather conditions stand in the Nation’s Capital.  With the exception of the last two days that have been unusually cool and wet, May has been considerably warmer than average.  Through May 13, Washingtonians had 3.69” of rain.  That puts this May close to the monthly average of 3.99” of rain over roughly the first two weeks.

No average high or low temperatures have been set so far this month, but the very warm weather that occurred from May 1 – May 11 produced a monthly average temperature of 67.2° (or 3.9° above average).  Although this month has been warmer than average, no 90° heat has occurred in the Nation’s Capital yet in 2019.  That’s unlike last May that saw three days of 90° heat in the first four days of the month.  DC has averaged between one and two days of 90° May heat dating back to 1993.  By comparison, this May 12 and 13 were uncharacteristically chilly in the Nation’s Capital with high temperatures of only 61° and 60°.  Such temperatures are more common in late-March.

Counting the 3.69” of rain so far this month, Washington, D.C. has had 16.75” of rain since January 1 (or 3.18” above average).  Although that’s not a large rainfall surplus by itself, DC Area residents can attest to just how wet the last 13 months have been.  The Nation’s Capital has a rainfall surplus of 30.98” from April 1, 2018 – May 13, 2019.  According to NOAA, the 12-month period through May 12, 2019 was the wettest such period on record in the Nation’s Capital with 71.05”.  Washington, D.C. averages 39.74” of rain in a given year.

There are two key differences between January 1, 2019 – May 13, 2019 and the same period last year.  January 2018 and March 2018 were both considerably drier than average and that contributed to a 2.31” annual rainfall deficit from January 1, 2018 through May 13, 2018.  That’s a net swing of 5.49” between the same period last year and this year.  To add to that, no measurable rainfall occurred in Washington, D.C. between May 1 and May 11 last year.  By comparison, measurable rainfall has occurred on seven days so far this month, including four days with at least 0.5” of rain.

However, unlike last May that had a dry start with a very wet second half of the month, May 2019 has gotten off to a very wet start.  A major shift is going to occur this week as a change in the position of the jet stream ushers in a wholesale change in the weather pattern for the United States.  NOAA’s 8-14 day outlook that extends through May 27 calls for warmer and drier than average conditions for much of the eastern United States.  That will help the water-logged DC Metro Area dry out.