Summer in October?

Great Falls National Park, Great Falls, Maryland

Washingtonians enjoyed a high degree of warm and dry weather conditions during the first three/+ weeks of October.  That continues the trend of recent Octobers in the Mid-Atlantic Region.  DC residents have experienced four of their 20 warmest Octobers on record over the last decade, according to NOAA.  That includes October 2007 – DC’s warmest on record since record keeping began in 1871.

The monthly average temperature (combining daily high and low temperatures) in the Nation’s Capital is 67.3° through October 22.  That will come down over the course of the week with significantly cooler and more seasonal temperatures on tap.  However, it’s been so warm for enough of the month to put this October in the conversation among DC’s warmest.  Nine of Washington, D.C.’s 10 warmest Octobers have occurred since National Airport opened in 1941. 

The warmest temperature so far this month was 86° on October 9 and 10.  That’s the average high on August 19.  Washingtonians had six days with high temperatures of at least 80° this month, the highest such total since 2007.  Since 1993, Washingtonians have had an average of more than three such days, with an 85° October day roughly every other year.  By comparison, Washington, D.C. averaged nearly two October days with low temperatures in the 30s in that time.  Some may wonder if there is a correlation between a warmer than average October and the upcoming winter season.  The short answer is no.

Of the District’s 10 warmest Octobers, it has gone on to have a warmer than average winter six times.  Washington, D.C. also had below average snowfall in seven of the 10 winters following those warmest Octobers.  Although Washington, D.C. averages a trace of snow (less than 0.01”) in October, none has occurred since October 2011.  The last time measurable snow occurred in Washington, D.C. in October was in 1979.

If the month were to end today, it would rank as the 17^th driest October on record with 0.83” at National Airport.  However, some much needed rainfall is on the way later today and tonight.  Over the last 20 years there has been an almost even split with eight drier than average Octobers and 11 wetter than average Octobers.  For those tired of warmer than average weather, cooler and more seasonal temperatures will soon arrive in the DC Metro Area.

Warmest Octobers (Washington, D.C. weather measurements made at National Airport, DCA):

1.  67.1° (2007)
2.  65.2° (1984)
3.  64.7° (1971)
4.  64.5° (1947)
5.  64.4° (1941)
6.  63.4° (1949)
7.  63.3° (1973)
8.  63.2° (1975, 1919)
10.  63.1° (2016)

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Driest Octobers (DCA):

1.  Trace (1963)
2.  0.02” (2000)
3.  0.29” (1874)
4.  0.34” (1896, 1892)
6.  0.40” (1920)
7.  0.44” (1944)
8.  0.53” (1882)
9.  0.59” (1998)
10.  0.65” (1912)

October “Names” to Remember in DC

Hurricane Opal makes landfall in October 1995  (Source: NOAA)

October has seen some notable Atlantic hurricanes, including some of most powerful ones on record, such as Wilma in 2005 and Mitch in 1998.  As recently as last year, Matthew became the Atlantic’s first Category 5 hurricane in nearly a decade.  Fortunately, none of these storms impacted the DC Metro Area.

While rare, DC and the Mid-Atlantic Region have felt the impacts of significant tropical or remnants of tropical systems in October including Hurricanes Sandy, Opal and Hazel.

Sandy (2012):  While not an unusually intense storm, what made Sandy memorable was its track.  At peak intensity, Sandy was a major Category 3 hurricane with sustained winds of 115 mph.  However, instead of heading harmlessly out to see, Sandy turned westward and made landfall in New Jersey on October 29.  Shortly before its landfall, Sandy was declared a “non-tropical” or “post-tropical” storm, meaning it had lost its tropical characteristics.

No matter what type of storm it was officially called when it made landfall, Sandy caused significant coastal erosion combined with flooding rainfall and damaging far well-inland.  It became one of the costliest systems on record, causing an estimated $75 billion in damages.  Sandy brought record rainfall and wind damage to the DC Metro Area on October 29-30.

Opal (1995):  Opal was one of five major hurricanes to form during the very active 1995 season.  It was also the strongest hurricane of the season with peak winds of 150 mph and a minimum central air pressure of 916 millibars (the lowest air pressure for a hurricane that didn’t reach Category 5 intensity).  Fortunately, it weakened to Category 3 intensity before making landfall near Pensacola, Florida on October 4.  Opal brought a significant storm surge to the U.S. Gulf Coast, with additional impacts far inland.  The DC Metro Area saw some severe weather from the remnants of Opal on October 5.

Hazel (1954):  Hazel remains a rare and record-setting storm more than 60 years after it made landfall.  On October 15, Hazel made landfall near Myrtle Beach, South Carolina as a Category 4 hurricane (sustained winds of 135 mph).  It tracked northward rapidly and caused devastation as far north as Canada.  It brought Washington, D.C. and New York City their highest wind gusts on record (98 mph and 113 mph, respectively).  Hazel remains the last Category 4 hurricane to make landfall anywhere in the United States during the month of October. 

Fortunately, there are no active tropical storms or hurricanes in the Atlantic Ocean this weekend and none are expected to develop in the next few days.  Nevertheless, this season has already set a slew of records and has been exceptionally damaging and deadly.  The World Meteorological Organization is all but certain to retire the names “Harvey,” “Irma” and “Maria,” following their horrific impacts.

Weather Quiz

True or False.

Washington, D.C. averages measurable snowfall during the month of October.

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Answer to September 29 Weather Quiz question.

True.  While past seasons have had multiple Category 4 hurricanes, but no season on record has had 2 or more make landfall in the United States.

A Warm and Dry Start to October

Washingtonians have gotten off to a significantly warmer and drier than average start to October. So far, only two days have featured cooler than average temperatures, while record warmth occurred on four consecutive days.  Also, DC residents finally saw some rain on October 8, which followed a streak of more than three weeks without measurable rainfall.

So far this month, there has been 0.83” of rain at National Airport which, while beneficial, is still below average.  Most of that rain came on October 9 when 0.56” fell – DC’s largest single day rainfall total since September 2 (0.77”).  The Nation’s Capital averages 3.40” of rain in October, so Washingtonians are currently at less than one-fourth of average for the month (0.83”).

Because September was significantly drier than average, the DC Metro area has been quite dry for more than six weeks.  That’s in contrast to July and August which, collectively, finished more than 7” wetter than average.  Over the last 20 years, the Nation’s Capital has had 11 wetter and 11 warmer than average Octobers.

However, four of the last five Octobers have been warmer than average.  This month has continued that trend so far.  The Nation’s Capital has averaged more than three days at/above 80° since 1993, with six such days so far this month.  That’s the highest total since 2007, which was DC’s warmest October on record.  The warmest temperature so far this month was 86° on October 9 and 10.  By comparison, NOAA data indicates 86° is Washington, D.C.’s average high temperature on August 19!

Perhaps this month’s most impressive feat amid all of the warmth was having four consecutive record high-low temperatures (October 8 – 11).  That means that the low temperatures on each of those days remained at record warm levels.  In fact, the low temperature of 75° at National Airport on October 8 not only set a record for the date, but set a record for highest low temperature for the entire month of October.  To help put that into perspective, the average high temperature in Washington, D.C. on October 8 is only 71°.

NOAA expects the warmer than average weather to continue for the next one to two weeks.  By comparison, parts of the western United States and Upper Midwest have already seen their first snowfall of the season.  The Nation’s Capital averages a trace of snow in October (less than 0.01”), with the last occurring on October 29, 2011.  Washingtonians don’t average measurable snowfall until the month of November (0.5”).