Approaching Record Territory

Memorial Day Weekend marks the unofficial start to summer

Washington, D.C. could have its warmest May on record as the final week of the month is poised to be significantly warmer than average across the Mid-Atlantic Region.  This month has already had a streak of 10 consecutive days of temperatures 80 degrees or warmer.  There have also been three days with temperatures in the 90s since May 1.  That’s remarkable since the average high in the Nation’s Capital doesn’t even reach 80 degrees until May 31.  This month has already had warmer than average temperatures on 17 of its first 23 days.

The warmest May on record came in 1991 when the average monthly temperature (combining daily highs and lows) was 73 degrees.  According to the National Weather Service, this month’s average temperature is 71.2 degrees through May 23 in the Nation’s Capital.  That puts us in good position to reach the 1991 record with high temperatures approaching 90 degrees starting tomorrow.  It’s hard to believe that such hot weather is on tap this week since the weather has been so comfortable the last few days. 

The same area of high pressure that’s brought the Mid-Atlantic Region stellar weather with comfortable temperatures and low relative humidity will move off the East Coast becoming a Bermuda High.  They are known as “Bermuda Highs” since that’s where they are typically centered.  Since the wind flow around an area of high pressure in the Northern Hemisphere is clockwise, the Nation’s Capital experiences warmer, more humid conditions when it’s on the west side of one.  For example, when the Bermuda High is in its typical summer position off the U.S. East Coast, it pumps warm, humid air northward from the Deep South into the Mid-Atlantic Region. 

As the temperatures increase this week, the relative humidity will also increase so it will feel quite sultry and uncomfortable out during the second half of the week.  The first heat wave of 2015 is possible this week.  A “heat wave” is defined as three consecutive days with temperatures of at least 90 degrees. 

In addition to being a warm month, it had also been a relatively dry month in the Nation’s Capital with only 1.91” of rain.  May averages more than twice that amount of rainfall in Washington, D.C.  This month will finish among the warmest May’s on record, but Washingtonians will have to wait and see if it will supplant May 1991 for the record.  My colleagues and I on the WUSA 9 Weather Team will keep you apprised of the latest weather forecasts this week as the weather heats up.