June’s Variable Weather

Today's Severe Weather Outlook  (Source: NOAA)

High temperatures today will reach the upper 80s and low 90s in spots.  That’s unlike June 20, 2010, when Washingtonians had a high temperature of 95° and were on day two of an 11-day heat wave.  Just nine years ago, DC residents experienced the warmest June on record with a monthly average temperature of 80.6°.  Meanwhile, this June has been very close to average (+0.3°) through yesterday with an average temperature of 74.0°.

Only two days had highs in the 90s, compared to June 2010 that had a total of 18 such days in the Nation’s Capital.  There haven’t been any heat waves yet this month (e.g., three or more consecutive days with high temperatures in the 90s).  However, Washingtonians could see the first heat wave of the month starting on Sunday.  While June 2010 was drier than average in DC (3.78”), this month has already exceeded the monthly average with 3.94”.  That makes June 2019 DC’s 12^th wetter than average month since April 2018.

An interesting comparison can also be made between June 2018 and June 2009.  Last June became DC’s first since 2009 that didn’t feature at least one heat wave.  There were only two 90° days in June 2009 compared to six such days a year ago.  Rainfall occurred in Washington, D.C. on 15 days in both June 2009 and June 2018.  While both June 2009 and June 2018 were wetter than average, June 2009 was the last time DC had a cooler than average June. 

Other similarities exist as well between June 2009 and last June.  For example, DC Area residents experienced a severe weather outbreak on June 3, 2009 that was concentrated in central and northern Virginia.  National Airport had 1.5” of rain, while Dulles Airport observed 2.69”.  Fast forward to June 19, 2018, when a few more instances of severe weather were reported in the DC Metro Area.  National Airport observed 1.12” of rain, while Dulles Airport had only 0.1”.  That helps illustrates how localized thunderstorms and severe weather often are during the summer months.

NOAA’s Storm Prediction Center has a significant portion of the Mid-Atlantic Region under a “slight” risk for severe weather this afternoon.  That means there is an increased potential for showers and severe thunderstorms to develop later today.  A thunderstorm becomes “severe” when it contains any of the following: 1) wind gusts of at least 58 mph; 2) hail 1”/+ in diameter; or 3) a tornado.  Severe thunderstorms sometimes contain multiple forms of severe weather.  Although heavy rain and lightning make any thunderstorm potentially dangerous, they do not make a thunderstorm “severe” by themselves.