D.C.’s Rainy and Cool Start to May

 

Mostly Sunny & Stellar Weather in Potomac, Maryland

The first eight days of May 2022 have been unusually rainy and cool in the Nation’s Capital.  It rained on six of the first eight days of May with a total of 3.30”.  Washington, D.C. averages 3.94” of rain during the entire month so D.C. residents have already had over 80% of May’s average rainfall.  The last two May’s have been drier than average in the Nation’s Capital so this month is already well-positioned to end that streak.

The wettest days of the month were May 6-7 with a 2-day rainfall total of 2.29” at National Airport.  It was also the first time since 2018 Washington, D.C. had at least two May days of 1.00”/+ of rain.  That’s not to say this month will end up being as rainy was May 2018 was with 8.73”, but this month has simply gotten off to a very wet start.

Temperatures were cooler than average on four of the first eight days of the month.  While today’s temperatures will be milder than yesterday, they will still be cooler than average in the Nation’s Capital.  May has already been 4.0° cooler than average in Washington, D.C. as of May 8.  In a relatively rare feat, the Nation’s Capital had highs in the 50s on May 7 and May 8.  Although D.C. also had consecutive highs in the 50s on May 29-30, 2021; it remains relatively unusual as the Nation’s Capital has averaged just one May day with highs in the 50s over the last 30 years. 

Washington, D.C. has had as many as five May days with highs in the 50s in May 2016, but 13 May’s since 1997 haven’t had any days with highs in the 50s.  By comparison, the Nation’s Capital has averaged close to two May days with highs in the 90s since the early 1990s, almost double the average number of days with highs in the 50s.  D.C. Area residents can expect 95°/+ May heat roughly once every five years.

Having a rainier than average May, as this month has been so far, doesn’t necessarily mean it will be a cooler than average month.  May 2020 and May 2021 were each cooler than average in the Nation’s Capital, but were also drier than average.  May 2018 and May 2019, for example, were each wetter than average and also rank among D.C.’s Top 10 warmest on record.

Unlike this month that’s gotten off to a cool and wet start, May 2018 got off to a hot and dry start.  No measurable rainfall occurred during the first 11 days of May 2018, when 10 days were also warmer than average.  That was followed by measurable rainfall on eight consecutive days from May 12 – May 19.  This month couldn’t have gotten off to a more different start than May 2018, but it doesn’t mean by any stretch that D.C. couldn’t see a warmer than average month this May.

NOAA’s Climate Prediction Center expects above average temperatures to envelop the D.C. Metro Area as the week wears on, but temperatures could be cooler than average again later in the month.  However, average daily temperatures continue to rise as May wears on.  That means while D.C. residents could enjoy highs in the low to mid 70s during the second half of May, that would still be cooler than average.  That’s because daily average high temperatures in the Nation’s Capital reach the upper 70s (78°) starting on May 21.

Notable May Severe Weather Events

 

U.S. Tornado Averages  (Source: NOAA)

May is one of the most active severe weather months of the year in the United States.  “Severe weather” is defined as a thunderstorm that produces any of the following: A) wind gusts of at least 58 mph; B) hail 1” in diameter or greater; or C) a tornado.  The most dangerous thunderstorms (supercells) can have more than one type of severe weather as large hail often precedes tornadoes.  Locally, the D.C. Metro Area has had a number of memorable May severe weather events.   

2019:  Three tornadoes touched down in central Maryland on May 30 with two EF-0’s and an EF-1 in Frederick and Howard Counties.  Wind damage was more widespread across the D.C. Metro Area with a wind gust as high as 66 mph reported at Davison Army Airfield in Fairfax County, Virginia. 

Just a week earlier more severe weather impacted the D.C. Metro Area.  An EF-1 tornado was confirmed in Columbia, Maryland that caused some structural damage.  There were also multiple severe wind gusts from the thunderstorms that developed.  Winds gusted as high as 66 mph at National Airport, 63 mph at Andrews AFB in Maryland, and 67 mph in Gaithersburg, Maryland.  Damage reports on May 23 ranged from downed trees and power lines to minor structural damage of homes and businesses.

2013:  The last EF-5 tornado in the United States occurred on May 20 in Moore, Oklahoma.  It had a long and destructive track as part of a larger, three-day severe weather outbreak.  The strongest tornadoes often develop from something called a “supercell thunderstorm,” which is a long-lasting thunderstorm that has a rotating updraft.

One of the supercell thunderstorms during this outbreak spawned the Moore, OK tornado.  Although not at EF-5 intensity during its entire track, it reached its peak intensity near the town of Moore with winds of greater than 200 mph.  According to NOAA, it remains the third costliest tornado on record having caused $2 billion in damage (unadjusted for inflation). 

2011:  A deadly EF-5 tornado devastated the town of Joplin, Missouri on May 22.  According to the National Weather Service, it was one of the deadliest in U.S. history with 122 fatalities and more than 700 injured.  NOAA also ranks the Joplin tornado as the most destructive on record in the United States, having caused an estimated $2.8 billion in damages (unadjusted for inflation).

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.

2007: The town of Greensburg, Kansas, was impacted by an EF-5 tornado on May 4 that was both destructive and deadly.  It was also significant for being the first tornado to be ranked an “EF-5” since the updated or “Enhanced” Fujita Scale went into operational use earlier that year.  This tornado is widely considered to be the strongest U.S. tornado since 1999.

1999:  The last observed F5 tornado in the United States occurred on May 3 before the Fujita Scale was updated or “enhanced” in 2007.  The town of Moore, Oklahoma also saw impacts from this devastating tornado that at the time was the third costliest tornado in the United States.  However, the $1 billion in damage it caused (roughly $1.4 billion in 2015 dollars) makes it “only” the sixth costliest tornado in U.S. history today.

 

May's Wild Weather in the Nation's Capital

 

April 2022 finished as a cooler and wetter than average month in the Nation’s Capital.  Not since 2019 have Washingtonians actually had a warmer than average April.  The third and final month of “meteorological” spring, temperatures will warm considerably during the month.

Daily average temperatures in the Nation’s Capital range from a high/low of 73°/54° on May 1 to 80°/63° by the end of the month.  D.C.’s hottest May temperature on record of 99° occurred on May 31, 1991.  Meanwhile, D.C.’s coldest May temperature of 33° occurred long ago on May 11, 1906.  D.C.’s May weather can also be quite streaky.  For example, while 11 of the last 20 May’s have been cooler than average, four of D.C.’s 10 warmest May’s have occurred since 2004.  By comparison, the last two May’s have each been cooler than average in the Nation’s Capital, following D.C.’s very warm May’s in 2018 and 2019. 

May is D.C.’s third wettest month of the year according to NOAA, with an average monthly rainfall total of 3.94”.  Rain can accumulate quickly in the Nation’s Capital this time of year as May 2018 illustrated.  It got off to a dry start with no measurable rainfall during the first 11 days of the month.  However, May 2018 finished as D.C.’s fourth wettest on record with a total of 8.73” of rain.  Nearly 70% of the monthly rainfall total occurred on just four days that each had over an inch of rain.  Despite the frequent rainfall during the second half of May 2018, all but there days of the month were warmer than average.

May is an active severe weather month in the D.C. Metro Area.  Looking at D.C.’s May climate records, one can see that on several dates a trace (enough to accumulate, but not enough to measure) of snowfall has occurred.  That wasn’t actually snow, but hail.  For example, on May 2, 2016 a severe weather outbreak produced a lot of hail in the D.C. Metro Area.  Small accumulations of hail were reported in spots such as at National Airport where a “trace” of frozen precipitation was observed.

Although summer doesn’t officially arrive until June, May often features summer-like heat.  D.C. has averaged between 1 and 2 days of temperatures in the 90s during the month of May over the last 30 years.  While no triple-digit May heat has been observed in the Nation’s Capital, D.C. residents can expect to see a high of at least 95° roughly once every 5 years.  NOAA’s Climate Prediction Center expects May 2022 to be warmer than average with near average rainfall in the D.C. Metro Area.