Summer’s Halfway Point

NOAA's Precipitation Outlook for late-July 2018

Meteorologists consider the three-month period of June, July and August to be “meteorological summer.”  That would make July 15 the approximate midway point.  During the first half of the summer, there were several important weather events in the Nation’s Capital.  Washingtonians experienced the city’s longest heat wave in nearly two years earlier this month and also set a new record for driest start to the month of July.

The period from July 7 through July 22 is the hottest time of the year in Washington, D.C. with an average high/low temperature of 89°/71°, according to NOAA.  A “heat wave” is defined as a minimum of three consecutive days with high temperatures of at least 90°.  DC residents experienced a seven-day heat wave from June 29, 2018 through July 5, 2018.  That was D.C.’s longest heat wave since a 12-day heat wave in August 2016.  Although not record-setting, D.C.’s July 16 high temperature of 98° was D.C.’s hottest temperature since July 20, 2017.  This hot weather has coincided with much drier conditions over the past few weeks, following a wet spring.  

The three-month period from April 2018 – June 2018 was DC’s wettest three-month period since 2014 and included DC’s sixth wettest May on record.  As weather records in Washington, D.C. date back to the 1870s, having a Top 10 finish is no small feat.  However, the rainy weather pattern that occurred for much of the aforementioned three-month period has changed dramatically.  

The previous record for driest first half of July occurred in 1900 when only a trace of rainfall (i.e. too little to measure) fell.   Meanwhile, no measurable rainfall has occurred in the Nation’s Capital since June 27, eclipsing the 1900 record.  However, scattered showers and thunderstorms have developed this afternoon, so the record streak of dry weather has come to an end today.

Given the wet spring in the Nation’s Capital, the area reservoirs and local water table are at satisfactory levels.  However, the combination of no rainfall over the last few weeks for much of the DC Metro Region combined with the hot weather has led to a reduction in soil moisture.  That’s why area gardens and lawns need to be watered.  NOAA expects wetter than average conditions in the Mid-Atlantic Region to continue over the final third of July.  Also, the tropics are more active in August and September, so the Mid-Atlantic Region could see beneficial rainfall from decaying tropical systems.