Is June Normally a Hot Month in DC?

The months of June, July and August comprise meteorological summer in the Northern Hemisphere.  The Nation’s Capital has had some memorable heat waves in June over the years.  Although rare, temperatures even reach the century mark in a Washington, D.C. summer.  More common, though, are temperatures in the mid to upper 90s.

The weather pattern during the summer months is often dominated by the “Bermuda High,” which is a semi-permanent weather feature.  It’s an area of high pressure typically situated off the East Coast of the United States not far from the island of Bermuda, giving it its name.  The clockwise winds around the high pressure system help usher in warm and humid air from the south and west of the Nation’s Capital.  The hottest days in Washington, D.C. are largely dependent on the wind direction.

Weather measurements for Washington, D.C. are made at National Airport.  A southerly wind ushers in more humid air with higher dewpoints from the southeastern United States.  It can also keep temperatures at National Airport slightly cooler than areas downtown as the wind blows off the cooler waters of the nearby Potomac River.  While higher relative humidity may make it feel more oppressive out, the hottest days in the Mid-Atlantic Region are those that are slightly less humid.

On the rare occasions temperatures eclipse the century mark in Washington, D.C., the winds have a more westerly component – meaning they blow from west to east.  That helps reduce the relative humidity, which is more favorable for higher air temperatures.  It might help to think of the southwestern United States where it’s very arid and triple digit heat is common over the summer.  During the past week, Phoenix, Arizona, had record heat with temperatures of 115 degrees on June 4.  Meanwhile in cities that are more humid, no triple digit heat has ever been observed in places like Tampa, Miami and Key West, Florida. 

There were only five instances of temperatures at or above 100 degrees at National Airport during the month of June since 1993.  That equates to one 100 degree day in June roughly every five years.  Temperatures in the mid to upper 90s are more common in Washington, D.C.  For example, Washington, D.C. has averaged nearly two days of temperatures from 95 to 99 degrees in June since 1993.  In contrast, there have been 21 days at or above 100 degrees during the month of July in the Nation’s Capital and seven such days in August since 1993.

2016 has been an unusual weather year thus far in the Nation’s Capital for several reasons, including the fact it hasn’t even been 90 degrees yet.  That is poised to change, though, with a few chances for temperatures to reach 90 degrees over the coming week.  You can find the latest weather headlines from my colleagues and me on the WUSA9 weather team both on-air and online.