The First Month of the Hurricane Season Concludes Today

Hurricane Arthur, July 2014 (Source: NOAA)

The month of June has been quiet in the tropical Atlantic.  That’s normal as the tropics usually don’t start to get active until later in the summer.  Check out this article I wrote for the WUSA9 website that explores what kind of hurricane season the experts are expecting.

Hot in D.C. !

The first significant heat wave of 2018 begins today in the Nation’s Capital.  A “heat wave” is defined as a minimum of three consecutive days with high temperatures of at least 90°.  Since several days with highs in the mid to upper 90s are on tap, it’s important to drink extra water and spend time indoors to prevent any heat-related stress.  D.C.’s hottest temperature so far this year was 95° on June 19. 

Although triple-digit heat is relatively rare in the Nation’s Capital, temperatures could reach 100° in parts of the D.C. Metro Area on July 1 and July 2.  The last time Washington, D.C. experienced triple-digit heat was on August 15, 2016 (100°).  In fact, August 15, 2016 was the third consecutive day that temperatures reached 100°/+ and that was only the third time that’s happened in the Nation’s Capital in the last 25 years.  The last time Dulles Airport in Sterling, VA and Baltimore, MD (measured at BWI Airport) reached 100° was July 25, 2016.

Although high temperatures will reach the low 90s in the D.C. Metro Area today, no record highs will be challenged.  Today is the sixth anniversary of D.C.’s hottest June temperature on record of 104° that occurred on June 29, 2012.  Below are the record high temperatures that could be approached in the D.C. Metro Area over the next few days.

June 30

Washington, D.C., National Airport (DCA): 100° (1959)
Dulles Airport, Sterling, VA (IAD): 98° (1964)
Baltimore, MD (BWI Airport): 100° (occurred most recently in 1959)

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July 1

DCA: 102° (1901)
IAD: 96° (2012)
BWI: 103° (1901)

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July 2

DCA: 101° (1898)
IAD: 98° (1966)
BWI: 103° (1901)

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July 3

DCA: 101° (occurred most recently in 1966)
IAD: 103° (1966)
BWI: 104° (1898)

Weather Quiz

A “heat wave” in the Nation’s Capital is considered a minimum of three consecutive days with high temperatures of 90° or greater.  When was the last time Washington, D.C. had a heat wave of at least 10 days ?

A.  1994

B.  2002

C.  2011

D.  2016

A Harbinger of Summer ?

NOAA's Temperature Outlook for July 2018

The Nation’s Capital has had a considerable amount of record June heat over the last 10 years.   June is also D.C.’s second wettest month of the year on average behind only May.  This June has been warmer and wetter than average in the Nation’s Capital.  Some may wonder if that foreshadows similar weather for the rest of the summer.  There are a few summers to look at for clues.

June 1994 was D.C.’s second hottest on record and featured a 14-day streak of 90° temperatures.  That was the hottest stretch of the entire 1994 summer and contributed to making June warmer than August.  Since June’s average monthly temperature in DC is nearly three degrees cooler than August, it’s rather unusual for June to be warmer than August.  June 1994 was also much drier than average with a monthly total of 1.59”, compared to the average of 3.78”.  While the summer of 1994 was drier and warmer than average in its entirety, July and August were closer to average than June 1994 was.

Washingtonians experienced the wettest June on record in 2006 with 14.02” of rain and was D.C.’s wettest month since August 1955.  The frequent rainfall also contributed to make June 2006 a slightly cooler than average month.  By comparison, the rest of the 2006 summer was drier and warmer than average in the Nation’s Capital.

Washingtonians experienced the second wettest June on record (11.94”) in 2015.  In a rare combination, June 2015 was also warmer than average with an average monthly temperature of 78.1°.  D.C. had 12 days with high temperatures in the 90s in June 2015, compared to an average of seven to eight such days since 1993.  While July 2015 was also wetter and warmer than average, August 2015 was drier and warmer than average.  In other words, there was no summer-long pattern.

This should help illustrate that while June’s dominant weather patterns can sometimes continue for much of the summer, June’s weather isn’t a reliable predictor of what the entire summer will be like.  One final example: the summer of 2011 was one of D.C.’s hottest on record and was also poised to be one of the driest as well.  However, the remnants of Hurricane Irene brought the D.C. Metro Area significant rainfall on August 27-28, 2011.  Consequently, August 2011 finished as D.C.’s wettest August since 1967.  NOAA expects this July to be warmer than average with near average precipitation in the D.C. Metro Area.

NOAA's Precipitation Outlook for July 2018

Lots of Rain

June has continued D.C.’s wetter than average trend that began in April.  The above average rainfall has been quite beneficial after a drier than average start to the year.  With a week left in June, it’s an open question of how much wetter than average this month will end up being in the Nation’s Capital.

 

According to the National Weather Service, Washington, D.C. had 24 drier than average months in the 31-month period from August 2015 through March 2018.  That led to a rainfall deficit of 16.42” of rain during that time period.  That’s why the last three months of above average rainfall has been generally welcome.  The last time three or more consecutive months had above average precipitation in Washington, D.C. was February 2014 through August 2014.

The calendar years of 2016 and 2017 were both several inches drier than average in the Nation’s Capital.  In addition, had it not been for D.C.’s second wettest June on record in 2015, that would have otherwise been a drier than average year as well.  Given the generally dry weather pattern the last three years, June 2015 can be considered an anomaly.

D.C.’s 31-month rainfall deficit that stood at 16.42” on April 1, 2018 has fallen to 8.92” through June 22.  So far in 2018, Washingtonians have a rainfall surplus of 6.24” as officially measured at National Airport.  Since April 1, there have been six different days with at least one inch of rain in the Nation’s Capital.  Such significant rainfall totals have led to localized flooding in parts of the Mid-Atlantic Region.  The most destructive flooding occurred on May 27 in Ellicott City, Maryland after a slow-moving complex of thunderstorms produced a few inches of rain.

From April 1 through June 22, D.C. residents got 17.32” of rain.  This is nearly 44% of what Washington, D.C. averages for an entire year !  That’s remarkable because it occurred without the heavy rain that a tropical system would bring.  

An extended period of time with wetter than average weather is exactly the type of pattern that’s ideal to make up a rainfall deficit.  As we’ve seen, too much rain all at once is not a good thing for flood prone communities.  NOAA expects near average precipitation in the D.C. Metro Area during the month of July.