Extreme May Temperatures

This weekend has featured some of DC’s coldest May weather in more than a decade.  Record low-high temperatures were set yesterday at all three DC Area airports.  The May 9 high temperature of 52° at National Airport tied the record low-high for the date, originally set in 1877.  One has to go back to May 1, 1963 (51°) for the last time Washingtonians had a May high temperature colder than yesterday’s.  Making matters worse, yesterday’s gusty northwest winds created wind chills in the 30s and 40s.

Low temperatures both yesterday (37°) and today (38°) fell into the 30s across the DC Metro Area.  That’s rare in the Nation’s Capital, especially on consecutive days.  Although not record-setting, both temperatures were much colder than DC’s average lows in the mid-50s during the second week of May.  The last time Washingtonians felt the 30s in May was 2005.

Weather records only date back to 1960 at Dulles Airport so there’s a much smaller pool of weather records.  The conditions are quite different between National and Dulles Airports.  There is a significant urban heat island effect at National, which also feels the influence of the Potomac River.  Conditions are more rural around the landlocked Dulles Airport and that helps create an ideal setup for radiational cooling.  Consequently, Dulles was colder both yesterday (33°) and today (33°).  Although not record-setting, that was much colder than average lows of 49° for May 9 and 10.  

In addition to National Airport, record low-high temperatures were also set at Dulles and BWI Airports yesterday.  Fortunately for those tired of the chilly and rainy conditions, temperatures today have been considerably warmer with highs in the 60s.  Temperatures will reach the 80s by the end of the upcoming work week.

Prior to this week, the last time DC residents experienced a daily high temperature in the 50s was on May 12, 2017 (59°).  There was a pivot to above average temperatures after that, with a high of 91° on May 17, 2017.  Although no temperatures that warm are on the horizon this week, Washingtonians would welcome even average temperatures in the 70s.  All but eight days have been cooler than average in the Nation’s Capital since April 10.  Residents of the DC Metro Area know to enjoy these cool temperatures, since the hazy, hot and humid conditions so common during the summer will be here soon.

May Temperature Extremes

NOAA expects a cooler than average May for the Great Lakes Region and New England

Today will be the warmest day for the rest of the week with highs in the mid to upper 60s.  While still below DC’s average in the low 70s, it will still feel nice after two days of high temperatures in the 50s.  That’s more like March than the first full week of May.

Temperatures are going to be below average in the DC Metro Area for the next seven to 10 days.  Some record low-high temperatures will be threatened, specifically this Saturday, May 9.  What that means is that high temperatures are expected to remain appreciably cooler than the daily average high, which for May 9 in Washington, D.C. is 74°.

The last time DC residents experienced a record low-high temperature during the month of May was in 2003.  May 2003 was an unusually cool and rainy month, which saw three record low-high temperatures tied or broken.  Before this week, the last time high temperatures remained below 60° in the Nation’s Capital in May was in 2017.  On the opposite end of the spectrum were May 2018 and May 2019, which each saw four days in the 90s, including three consecutive days that made for a “heat wave.”  

NOAA’s Climate Prediction Center expects this month to be more like May 2017, which finished cooler and wetter than average.  There have already been two days this month with high temperatures in the 50s.  This weekend is setting up to be especially cold in the Nation’s Capital with low temperatures in the 30s for much of the DC Metro Area on both Saturday and Sunday mornings. 

A cold rain returns to the DC Metro Area on Friday afternoon and it could end with a few snowflakes early Saturday morning in areas north and west of town like Leesburg, Virginia and Clarksburg, Maryland.  The latest in the season snow has fallen in the Nation’s Capital was when a trace occurred on May 10, 1906.  The last time Washington, D.C. dipped below 40° in May was on May 3, 2005 when it was 38° at National Airport.  Having such unseasonably cold May weather is particularly hard to imagine since four of DC’s 10 warmest May’s have occurred just since 2012.  Whether or not any snowflakes fall in the DC Metro Area late Friday night / early Saturday morning, conditions will be ideal for patchy frost both Saturday and Sunday mornings.

This helps illustrate how streaky May weather can be in the Nation’s Capital.  Seven of the 10 May’s between 2000 and 2009 were cooler than average in Washington, D.C., while eight of the following 10 through 2019 were warmer than average.  If May 2020 finishes cooler and wetter than average month, then that would make 2020 the first year the Nation’s Capital has had both a cooler and wetter than average April and May since 2003. 

Record Low-High Temperatures (Source: NOAA)

May 9:

Washington, D.C., National Airport (DCA): 52° (1877)
Dulles Airport, Sterling VA (IAD): 55° (1977)
BWI Airport, Baltimore, MD: 53° (1977, 1947)

Weather Quiz

When was the last time Washington, DC had a May temperature in the 30s ?

A.  1992

B.  2003

C.  2005

D.  2009

May Gets Underway

Germantown, Maryland (Courtesy: Susan Granzow)

April 2020 finished as DC’s seventh wettest on record with 6.30” of rain, more than double the monthly average of 3.06”.  It also finished 1.5° cooler than average.  Those factors combined to make April 2020 only DC’s third cooler and wetter than average April since 2001.  Last month’s below average temperatures were partially a function of the 16 days with measurable rainfall.

Nine of the last 20 May’s have been cooler than average in the Nation’s Capital.  However, that hides how streaky May weather can be.  While seven of the 10 May’s between 2000 and 2009 were cooler than average in Washington, D.C., eight of the following 10 were warmer than average through 2019.  Average high/low temperatures in the Nation’s Capital range from 71°/52° on May 1 to 80°/61° on May 31.  DC’s hottest May temperature remains the 99° temperature on May 31, 1991.  By contrast, DC’s coolest May temperature on record is 33° from May 11, 1906.  

On average, the month of May is DC’s wettest month of the year with 3.99”.  Eleven of the last 20 May’s have been drier than average in Washington, D.C.  However, four of DC’s 10 wettest May’s have occurred just since 2003.

May weather can be very streaky as Washingtonians saw in 2018.  That May got off to a dry start with no measurable rainfall during the first 11 days of the month.  However, May 2018 finished as DC’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 abundance of rainfall, May 2018 finished as DC’s third warmest.  The big difference between last month and May 2018 is that 17 of the 30 days last month were cooler than average, while all but three days in May 2018 were warmer than average.  That helps illustrate that while rainy and cool weather often go hand in hand, they aren’t always positively correlated.  

With the exception of yesterday’s average high of 72° and today’s anticipated highs in the 70s, much of the upcoming week is going to be cooler than average.  NOAA’s Climate Prediction Center expects May to be both cooler and wetter than average in the DC Metro Area.  May 2017 was the last time Washingtonians experienced a cooler and wetter than average May.