DC’s Strange May 2021 Weather

 

A Beautiful Day at the Avenel Park, Potomac, Maryland

May is poised to finish as a cooler than average month in Washington, D.C. for a second consecutive year.  That’s the first time there have been back-to-back cooler than average May’s in the Nation’s Capital since 2008-2009.

DC’s weather has been very streaky this May with 14 of the first 18 days cooler than average.  That’s given this month an average temperature (combining daily high/low temperatures) nearly 3° cooler than average through May 18.  Washingtonians then experienced weather more characteristic of mid-summer with highs in the 90s on four out of seven days between May 20 and May 26.  The very warm week in the Nation’s Capital led DC’s average monthly temperature to soar from being 2.7° below average on May 18 to within 0.5° of average on May 27. 

Temperatures plummeted, however, over the weekend.  DC’s high temperatures of 59° and 58°, respectively, on May 28 and May 29 were more characteristic of mid-to-late March than Memorial Day Weekend.  While not quite record-setting in the Nation’s Capital, record low-high temperatures were set at both Dulles and BWI Airports.  Today’s high temperatures have rebounded to the 70s, but that won’t be enough to prevent May 2021 from finishing as a cooler than average month overall.  

That shouldn’t come as much of a surprise, though, as temperatures have been cooler than average on 19 of May’s 31 days in Washington, D.C.  It won’t be as cool as last May was in the Nation’s Capital as temperatures will finish nearly a degree cooler than average this month, while May 2020 finished more than 2° below average.  That can largely be attributed to the fact DC had four days of 90° heat this month, while last May didn’t have any.

Despite more than 3” of rain in the Nation’s Capital over the last week, May 2021 will still finish with below average rainfall.  That’s the result of the very dry first portion of the month, which had a combined total of only 0.69” of rain through May 23.  Washington, D.C. is now poised to finish with 3.77” of May rainfall.  Fortunately, following the rainy and cool last few days, Washingtonians are in store for a sunnier and milder start to the week.  The National Oceanic and Atmospheric Administration (NOAA) expects warmer than average June temperatures in the DC Metro Area with near average rainfall.

The Rarest of the Rare

 

NOAA's Tornado Averages By State

Tornadoes are ranked on the Enhanced Fujita Scale that starts with a minimal EF-0 that has winds of 65 – 85 mph.  The strongest tornadoes are ranked an EF-5 with winds of greater than 200 mph and are rare.  The United States is currently in a record stretch without a single EF-5 tornado reported in the United States in more than eight years since May 20, 2013.

2013:  Several dozen tornadoes occurred in the Midwest during a two-day severe weather outbreak on May 19-20.  The most devastating was on May 20 in the city of Moore, Oklahoma.  An EF-5 tornado touched down and caused widespread damage and a number of fatalities.  Since this tornado developed so quickly and was so intense – with winds greater than 200 mph – it was especially damaging and deadly.  According to NOAA, it caused two dozen fatalities and remains the third costliest tornado on record having caused $2 billion in damage (unadjusted for inflation). 

2011:  The town of Joplin, Missouri experienced a devastating EF-5 tornado on May 22.  The Joplin EF-5 remains the costliest tornado on record having caused $2.8 billion in damages (unadjusted for inflation).  With a total of 181 fatalities, it was also the single deadliest U.S. tornado since 1947.  The spring of 2011 was an unusually active severe weather season for the United States with a total of six EF-5 tornadoes.  That was the highest annual total since 1974.

1999: An F5 tornado occurred in the Oklahoma City suburb of Moore on May 3.  Wind of more than 300 mph were reported from a mobile Doppler radar that helped track this devastating storm.  This tornado ranked among the costliest in U.S. history and was the last observed F5 tornado in the United States before the Fujita Scale was updated or “enhanced” in 2007.  Many of the same areas would be impacted again by the devastating May 2013 EF-5 tornado.

While the April 2002 La Plata tornado in Charles County, Maryland remains the strongest tornado on record in the state of Maryland at F4 intensity, it would be ranked as an EF-5 on the updated Fujita Scale if a similar tornado were to occur today.  Fortunately, no severe weather is expected in the Mid-Atlantic Region over the Memorial Day weekend.

 

Summer Arrives in the Nation’s Capital!

 

Area pools will be opening for the season soon

The first half of May 2021 was both cool and dry in the D.C. Metro Area.  However, there has been a major shift in the weather pattern over the last week that has left the Nation’s Capital feeling more like summer.

Washingtonians had a monthly average temperature 2.7° cooler than average through May 18.  There was a dramatic shift since then with six warmer than average days over the last week.  There were three days in the 90s since May 20 and that’s helped the monthly average temperature quickly rise to being within 0.5° of average.

This month has also been quite dry with only 1.03” of rain as of May 25.  There are several rain chances over the last few days of May, so that number is all but certain to increase.  That’s a good thing since if May were to end today, it would finish as D.C.’s driest since 1986.  Washington, D.C. has had less than 2” of rain in May only three times in the last 20 years, most recently in 2015.

May 2015 was a unique weather month as it finished as D.C.’s warmest on record.  It was also an exceptionally dry month with only 1.92” of rain – roughly half the average.  Having a warm and dry May isn’t a good harbinger of what the upcoming summer will be like.  That’s because rainfall from scattered showers and thunderstorms during the summer months in the Mid-Atlantic Region is often spotty and unreliable.

May 2020 was an exception to that rule.  Last May was cooler and drier than average in the Nation’s Capital for the first time since 2006.  However, last summer was warmer and wetter than average.  That was in large part due to D.C.’s record number of 90° days last July (28) in conjunction with several exceptionally wet days.  There was a total of six days last summer that had 1”/+ of rain, including three days with at least 2” of rain. 

The Nation’s Capital has a 2021 rainfall deficit of nearly 2”, so any rainfall would be beneficial.  That’s not what beachgoers want to hear heading into Memorial Day weekend, but there are several rain chances during the next few of days.  May 2021 could finish with near average temperatures and rainfall.  NOAA’s Climate Prediction Center is expecting a warmer and wetter than average summer in the Mid-Atlantic Region.