Fall Extremes

Glen Echo Park, Glen Echo, Maryland

The weather pendulum has swung in the Nation’s Capital.  The hot and dry weather conditions that dominated headlines for much of the last three months are gone.  On September 25, the Nation’s Capital was well-positioned to finish as the 5^th driest September on record with only 0.51” of rain to that point.

However, the significant amount of rain this week has knocked this month out of contention for being one of the driest on record.  This week’s rainfall has been beneficial, though, helping put a dent in the annual rainfall deficit.  Nevertheless, the combination of hot temperatures over the last several months and below average rainfall have combined to create abnormally dry conditions across much of the Mid-Atlantic Region according to the Drought Monitor Index.  That’s much to the consternation of area gardeners and farmers.

As is typical this time of year, the weather pattern can quickly shift from being drier than average to being quite wet.  Localized flooding has occurred this week in parts of the Mid-Atlantic Region.  From Monday, September 26 through last night, 1.99” of rain fell at National Airport.  Rainfall amounts of more than double that have occurred in areas east and west of the immediate DC Metro Area.  Additional rainfall has occurred this morning making the six consecutive days of measureable rain in Washington, D.C. the longest such streak since the spring, when rain occurred at National Airport on fifteen consecutive days between April 27 and May 11.

This week’s rainfall at National Airport has been its highest five day September total since 2011.  Back on September 5 – 8, 2011, a total of 6.93” of rain fell at National Airport (almost double September’s average of 3.72”),   due to the remnants of Tropical Storm Lee.  Significant rainfall can also occur in the fall without a tropical system.  Such was the case in 2010 when 5.31” of rain occurred in Washington, D.C. from September 26 – 30.  If atmospheric steering currents are weak and heavy bands of rain are able to pass over the same areas over and over (a meteorological phenomenon known as “training”), then heavy rain and flooding can ensue.

Area residents have been understandably nervous about this week’s persistent rainfall after the devastating flooding that occurred in Ellicott City, Maryland in late July.  That’s why following flood safety tips are vital irrespective of season.  Never drive through water covered roadways and make sure areas of poor drainage on your property are clear when heavy rain is forecast.  You can rely upon your favorite meteorologists, such as my colleagues and me on the WUSA9 Weather Team, for the latest weather updates.