June’s Sultry Conclusion in the Nation’s Capital

Today will likely become DC’s hottest day of the year with highs in the mid to upper 90s.  If today’s temperature reaches 95° at National Airport, it will not only be the hottest day of 2021, but will also be DC’s first 95°/+ temperature in almost a year (July 27, 2020). 

Today will also be DC’s third consecutive 90° day – giving Washingtonians their second heat wave of the month.  June 2021 will be DC’s third consecutive June to end with a heat wave.  The 90° heat in the D.C. Metro Area today will be particularly oppressive as dewpoint temperatures have reached the low to mid-70s.  Hot temperatures and uncomfortable relative humidity levels combine to produce dangerous heat index temperatures.  The “heat index” is the feels-like temperature when combining air temperature with relative humidity.

June 2021 will finish with seven days in the 90s.  That’s compared to the six days that high temperatures remained in the 70s.  What stood out the most in terms of DC’s June weather has been the stretches of almost fall-like weather.  From June 15 – June 18, temperatures were not only cooler than average with highs in the low to mid-80s, but dewpoints were also uncommonly low in the 40s and 50s.  There was an encore performance from June 22 – 25, when highs remained in the upper 70s and low 80s with similarly low dewpoints.

These stretches of comfortable weather were largely offset by DC’s two heat waves this month.  Average monthly temperatures will finish roughly 0.5° warmer than average.  That’s not surprising given the near even split of comfortable weather days and DC’s two heat waves since June 1. 

Finally, June 2021 will finish with 5.48” of rain, more than one inch above the June average of 4.20”.  The warmer the air temperature, the higher its capacity is to hold water vapor.  That’s a key reason why heavier rain events tend to occur during the summer and early fall when temperatures are warmest in the Nation’s Capital.  The majority of this month’s rainfall (4.62”) occurred on just three days between June 10 – June 14.