Independence Day Weather Conditions

Area residents and tourists have been lucky this week with temperatures across the DC Metro Area feeling more like early September than late June.  Today’s expected high temperatures near 80° more closely resemble the average temperatures for Labor Day than the week before Independence Day.

That’s a big change from the often stifling heat and humidity the last week of June and early July.  Over the last 20 years, Washingtonians have experienced 100° heat at least once between June 24 and July 8 on four separate occasions.  Area residents have endured 95° heat in eight of the last 20 years over the same two-week period.

An exceptionally rare and record-setting heat wave occurred in the Nation’s Capital from June 28 through July 8, 2012.  High temperatures were at least 95° on 11 consecutive days, with high temperatures of 100° or greater on five of those days.  Washington, D.C. set a new record high temperature for the entire month on June 29 (104°) and DC’s second hottest temperature occurred on July 7, 2012 (105°).  That’s just one degree below the city’s hottest all-time temperature of 106° that’s occurred twice (in 1918 and 1930).

Rain and severe weather have also frequently interrupted the July 4 holiday.  Washington, D.C.’s wettest July 4 occurred in 2004 when 2.18” of rain fell.  Severe weather also affected an untold number of barbecues and fireworks displays in and around the DC Metro Area in 2006, 2007 and 2008.  Washington, D.C.’s record high on July 4 is 100° (1919), although it reached 99° in 1999, 2002 and 2012.  By comparison, the July 4 holiday last year was DC’s coolest (74°) since 1941.

Temperatures this week have been cooler than average with comfortable, fall-like relative humidity.  However, as nice as the weather this week has been, the Nation’s Capital could use some rain.  Washington, D.C. could have its third driest June on record if no more rain occurs this month.  

Washington, D.C.’s Driest Junes as measured at National Airport (Source: NWS)

1.  0.86” (1940)

2.  0.95” (1988)

3.  1.06” (as of June 26, 2017)

4.  1.21” (1976)

5.  1.24” (1954, 1894)

DC’s Dry Weather Pattern Returns

The Nation’s Capital is having another drier than average month following its first wetter than average month of 2017.  Dating back to August 2015, Washingtonians are dealing with a rainfall deficit of nearly 14” as of June 22.  That deficit is 10.34” at National Airport just since June 1, 2016.  Fortunately, the wetter than average May helped eliminate the moderate drought conditions that had enveloped parts of the DC Metro Area.

However, following a warm and dry June, May appears to have been an anomaly rather than the start of a streak of wetter than average months in the Nation’s Capital.  While the remnants of Tropical Storm Cindy brought parts of the Mid-Atlantic Region beneficial rain, the DC Metro Area saw precious little rainfall.  In fact, Washingtonians have had a total of only 1.06” of rain the entire month, compared to the June average of 3.78”.  

Acerbating this month’s dry conditions have been the warm temperatures.  While having six days with high temperatures in the 90s so far this month isn’t unusual, overnight low temperatures have been above average.  Washington, D.C. is on a streak of 14 consecutive days since the last time temperatures last fell below 70° on June 10.  That’s significant because the average low temperature doesn’t rise to 70° in the Nation’s Capital until June 28.

Area residents shouldn’t be concerned, though, about the lack of rainfall this month.  The Mid-Atlantic Region has had some exceptionally wet Junes in recent years with three of DC’s wettest June’s on record just since 2006 according to the National Weather Service.  Rainfall deficits can be made up in a hurry this time of year such as on June 25-27, 2006 when a total of 10.34” of rain occurred at National Airport.  June 2006 ultimately became the wettest June on record in Washington, D.C. (14.02”).

However, with only 1.06” of rain so far this month and no significant rain chances in the next week, this June could become one of the driest on record in Washington, D.C.  If June were to end with 1.06”, than that would make it the third driest June behind only 1940 (0.86”) and 1988 (0.95”).  Those were the only two years where June finished with less than an inch of rain in Washington, D.C.  More recently, there have been three Junes in the last 15 years that finished with less than two inches of rain.  All three were warmer than average.

There’s Action in the Tropics

Tropical Storm Cindy in the Gulf of Mexico (Source: NOAA)

The Atlantic Ocean has had three tropical storms so far this year: Tropical Storm’s Bret and Cindy both developed just this week.  Although June tends to be one of the quieter months of the six-month hurricane season, named storms do sometimes occur.  Over the last decade they have occurred fairly regularly.

At least one tropical storm has formed in the month of June in seven of the last 10 years.  To add to that, there has been a named tropical storm prior to the start of hurricane season (June 1) in half of the last 10 seasons.  Just last year, Hurricane Alex was an exceptionally rare January hurricane.  Tropical storms that develop early in the season tend to form in the Gulf of Mexico or Caribbean Sea where sea surface temperatures are warmer and environmental conditions are generally more favorable. 

This week marks the 45^th anniversary of the remnants of Hurricane Agnes, which caused catastrophic flooding in the Mid-Atlantic Region.  Agnes was the costliest tropical cyclone in U.S. history at the time.  The fact that Agnes at peak intensity was only a minimal hurricane illustrates that a tropical system doesn’t have to be intense to have significant impacts.  Also, Tropical Storm Allison, in June 2001, caused some of the worst flooding on record along parts of the U.S. Gulf Coast.  Allison remains the only tropical storm to have had its named retired.  

The new Tropical Storm, Cindy, will have similar impacts along the U.S. Gulf Coast where it’s bringing copious amounts of rainfall.  There will be widespread flooding from Texas to Georgia and northward where the remnants of Cindy track.  A common misconception is only people on or near the coast can feel the impact of a landfalling tropical system.  The truth is people living hundreds of miles inland often feel significant impacts from tropical systems.  For example, the remnants of Hurricane Floyd brought flooding rainfall to the DC Metro Area in 1999 after its landfall in North Carolina.

Experts expect the 2017 Atlantic hurricane season to be a near to slightly busier than average.  According to Dr. Philip Klotzbach of Colorado State University, this hurricane season has gotten off to a fast start with 2017 being only the fifth season in the last 130 years to have at least three tropical storms by June 20.  The last hurricane to form in the Atlantic Ocean during the month of June was Hurricane Chris in 2012.  The strongest June hurricane on record in the Atlantic Ocean was Category 4 Hurricane Audrey in 1957.