Current Heat Wave Disappoints

Although this week’s heat wave resembles recent heat waves in the DC Metro Region, it falls way short of historical heat waves.  The National Weather Service defines a “heat wave” as a minimum of three consecutive days with temperatures of at least 90 degrees.  With 90-degree heat expected through Saturday, that would make our current heat wave five days long.  Two things in particular have contributed, though, to make this week’s heat wave memorable.

Prior to Washington, D.C.’s high temperature of 91 degrees on Tuesday, July 5, the last time it had been at least 90 degrees in the Nation’s Capital was on June 21.  To add to that, the two days prior had been unseasonably cool with high temperatures of only 74 degrees at National Airport – more typical for early May or late September.  While the low 90s felt especially hot after high temperatures in the mid-70s, 91 degrees is only slightly warmer than the average high of 88 degrees in Washington, D.C. on July 5.

During the last three years, there were a total of four heat waves of at least five days, with the longest one being a 13-day stretch last summer from July 24 - August 5.  While the hottest temperature to occur during last summer’s event was 96 degrees, it’s already been 96 degrees this year in Washington, D.C. (on June 11) and temperatures will approach that again today and tomorrow.  However, no triple digit heat has occurred during any of these heat waves.

By comparison, the summers of 2010 – 2012 featured some of the hottest weather on record in the Mid-Atlantic Region.  There was a total of 67 days of 90-degree heat in 2010 in Washington, D.C. which tied 1980’s record for highest such number.  Next was July 2011 that was not only the hottest July in the Nation’s Capital, but the hottest month on record with 25 days at or above 90 degrees – including 3 days of triple digit heat.  The hottest part of the 2012 summer in Washington, D.C. was an eleven-day heat wave from June 28 – July 8.  That hot spell included five days of triple digit heat.  The record for longest “heat wave” in Washington, D.C. is 21 days that occurred twice during the hot summers of 1980 and 1988.

The fact that this week's heat wave won’t approach the hot weather benchmarks that were set during past summers should be a comfort to some.  All heat waves can be dangerous, though, so it’s important to remember to take precautions including minimizing your time outdoors, drinking extra of water and doing outdoor activities early in the day as much as possible when it’s cooler.