Where has the Triple Digit Heat Gone?

Prado Museum, Madrid, Spain

Triple-digit heat is a rarity for the Mid-Atlantic Region.  That’s because triple-digit temperatures are most common in arid climates away from water.  However, summers in the Nation’s Capital often feature very humid weather.  When the air is more humid, it cannot heat up or cool down as quickly.  Washingtonians typically experience 100 degree heat only every few years.  That makes the 2010 – 2012 summers unusual since triple-digit heat occurred in the Nation’s Capital multiple times. 

 

The summer of 2012 was particularly memorable since there were eight days that were at least 100 degrees.  Meanwhile, this summer has been the warmest in the Nation’s Capital since 2012, with the highest number of 90 degree days since then (53 to 39 so far in 2015), but no triple-digit heat.

Although no record highs have been set in the Mid-Atlantic Region this summer, that’s not the case in Europe where multiple record highs have been set.  In Spain, Madrid’s hottest June temperature on record of 104 degrees occurred on June 30.  London’s hottest temperature on record of 98.1 degrees occurred on July 1.  Meanwhile, Warsaw, Poland had its hottest August temperature on record this past Saturday when it was 97.9 degrees.

It’s also important to note that the National Weather Service followed up on recent assertions by some area scientists and the media that temperature readings at National Airport appeared unusually high compared with nearby suburban areas.  Upon investigating, Jim Lee, the Meteorologist-in-Charge of the Sterling, VA, NWS office said: “It looked like it [the sensor] was reading 1.5-2 degrees too high,” at National Airport.  So technicians replaced it on Monday and it’s expected that will reduce falsely high temperature differences in the DC Metro Region.  

Some Perspective on the Summer of 2015

A Beautiful July Sunset!

Washington, D.C.’s longest heat wave in several years concluded this past week when National Airport’s 13 day streak of 90 degree heat ended on August 5.  Not since 2011 had there been a streak of more than 11 consecutive days with high temperatures of at least 90 degrees.

The hottest temperature measured during this nearly two week stretch was 96 degrees on August 4.  Although this summer’s total of 38 days of 90 degree temperatures is the highest since 2012, it’s near the seasonal average of 36 days in the Nation’s Capital.  While 2015 has featured appreciably more 90 degree heat than last year (when there were only 24), no record highs have been set this summer.

On the other hand, Baltimore has seen only 17 days of at least 90 degrees and Dulles Airport has seen only 11 such days.  While National Airport’s longest “heat wave” of 2015 was the recent 13 day stretch with temperatures greater than 90 degrees, Dulles and BWI Airports haven’t seen more than three consecutive days of at least 90 degrees this year.  This summer’s heat in the Nation’s Capital can at least partially be attributed to the “urban heat island effect."

July’s average temperature at National Airport was almost two degrees warmer than average at 81.5 degrees, while at Dulles Airport it was only 76 degrees (almost a degree cooler than average).  Baltimore’s average temperature in July was exactly average at 77 degrees – combining daily highs and lows.  Although being away from major urban areas helps keep those locations cooler than downtown Washington, D.C., more study is needed as to why the temperature is consistently so much warmer at National Airport (the official weather reporting site for the Nation’s Capital).  

August often features an appreciable amount of hot weather, but average high temperatures gradually fall from 88 degrees to 84 degrees by the end of the month.  So Washingtonians looking forward to fall should be able to notice a difference to their liking as the month wears on.  That’s not to say that conditions won’t remain ideal for a trip to the beach until well into September.  My colleagues and I on the WUSA9 weather team will keep you apprised of the latest weather forecasts – including when any 90 degree temperatures may return this summer.