The Hottest Week in Four Years

July 25 Record Highs  (Source: WUSA9)

Washingtonians multi-year streak without triple-digit heat came to an end on July 25, 2016 when the high temperature reached 100 degrees.  Today marks the fourth anniversary of the last time thermometers in the Nation’s Capital reached the century mark.

Extreme heat has led to the issuance of heat advisories and excessive heat warnings from North Dakota to Louisiana to New York over the last week.  That includes cities in the I-95 corridor from Washington, D.C. to New York City.  Dulles Airport in northern Virginia set a new record high of 100 degrees on July 25.  Baltimore also reached 100 degrees, tying its record for the date.  Newark, New Jersey set a new record high of 99 degrees on July 25, while Philadelphia tied its record high of 96 degrees. 

During the current heat wave some may have heard the term “heat dome.”  That’s a fancy term used to describe a sprawling area of high pressure that’s dominated the weather across much of the Central and Eastern United States.  High pressure is characterized by sinking air which suppresses cloud development and facilitates the hazy, hot and humid conditions.  However, it’s not a new phenomenon as sprawling areas of high pressure typically dominate much of the United States during the summer months.

Meanwhile, the intensity of the current heat wave has been the most significant since 2012 for the Mid-Atlantic Region.  A “heat wave” is defined as a minimum of three consecutive days with temperatures of at least 90 degrees.  DC’s current heat wave began on July 21 and is poised to continue until this weekend.  That would give July 2016 a total of 23 days of 90-degree heat, one of the highest such totals on record (July 2011 had the most 90-degree days in a calendar month in the Nation’s Capital with 25).

That’s why it’s so important to drink plenty of water, spend time in air conditioning and do any outdoor errands or chores early in the day or after dark.  My colleagues and I on the WUSA9 weather team will keep you apprised of the latest weather forecasts both on-air and on the free app for your mobile devices.

Weather Quiz

What is the official definition of a heat wave in the Nation’s Capital?

A.  1 day of temperatures 100 degrees or hotter.

B.  3 consecutive days of 90 degrees or hotter.

C.  4 consecutive days with a heat index or “feels-like” temperature of 95 degrees or hotter.

D.  5 consecutive days of 85 degrees or warmer.

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Answer to Weather Quiz question from July 14.

What good timing for this question with some of the hottest weather in several years during the last week across much of the central and eastern United States.  Although the hottest temperature on record (106 degrees) in the Nation’s Capital has occurred twice – once in July and once in August – the highest annual average high temperature in Washington, D.C. is 89 degrees from July 7 to July 22.

Putting the Heat in Perspective

Forecast for Washington, D.C.  (Source: WUSA9)

Although the most significant heat wave in several years began yesterday when the high temperature reached 90 degrees in the Nation’s Capital, the dangerous heat will arrive today.  It’s already been a dangerously hot week across much of the country with heat advisories in effect today from South Dakota to Louisiana to Ohio.  While heat advisories and excessive heat warnings are often issued on a localized basis during the summer months, the extent to which they’re currently in effect is unusual.  Here is a good National Weather Service link that explains the different criteria for heat advisories.

Triple digit heat is relatively rare in the DC Metro Region.  While there have been a total of 32 days at or above 100 degrees in Washington, D.C. (measured at National Airport) since 1993, there have been only seven instances of two or more consecutive days at or above 100 degrees.  Six of those streaks have occurred in July, with the longest being a four day stretch from July 5 – 8, 2012.  The summer of 2010 was the first summer in the Nation’s Capital to feature five or more days at or above the century mark since 1997.

Given the potentially historic heat on tap for the next few days across the eastern United States, it’s a good time to review some of the historical heat waves in Washington, D.C.  During the last 25 years, triple-digit heat has occurred in the Nation’s Capital roughly every three to five years.  Since 1993, there have been consecutive days of triple-digit heat five times in July.  Triple-digit heat has also occurred during five June’s and August’s in that time.  However, July has had the highest total number of days (20) at or above 100 degrees.

The hottest temperature on record is 106 degrees in Washington, D.C., which occurred twice – both times were before National Airport opened in 1941.  The hottest temperature on record at National Airport is 105 degrees which occurred on July 7, 2012 and August 17, 1997.  The hottest temperature on record at Dulles Airport in Sterling, Virginia is 105 degrees on July 22, 2011.  Meanwhile, Baltimore’s hottest temperature on record is 107 degrees on July 10, 1936.

Although not typical in this part of the country, the thermometer will approach 100 degrees during the next few days.  Even if there isn’t any triple-digit heat the next few days, high temperatures are poised to be in the 90s for the balance of next week.  My colleagues and I on the WUSA9 weather team will keep you apprised of the latest weather forecasts – and if any record highs are set.