The Winds of Change

Washingtonians have experienced a dramatic shift in the weather pattern in what has become the coldest weather yet of the fall season.  Through November 19, this month had been four degrees warmer than average in Washington, D.C. with an average temperature of 55.5 degrees (combining daily high and low temperatures).

Contributing to that warmth were the high temperatures this past Friday and Saturday, November 18 and 19 (70F and 72F).  That was the first time DC residents experienced consecutive highs in the 70s after November 15 since 2011. High temperatures in the low 70s are more characteristic of early October than mid-November in Washington, D.C.  A powerful cold front brought an abrupt end to the unseasonal warmth over the weekend.  Yesterday’s high temperature of 47 degrees made Sunday a whopping 25 degrees colder than Saturday.  Sunday was the coldest day in the Nation’s Capital since April 5 (46F). 

Unfortunately, Saturday’s cold front only brought a scant amount of rainfall to the DC Metro Region (0.05” at National Airport).  It has been very windy and that led the National Weather Service to issue wind advisories.  (Wind advisories are issued when sustained winds of 31 to 39 mph or wind gusts of 46 – 57 mph are expected for 3 or more hours.)  The highest wind gust to occur at National Airport over the last two days was 49 mph.  The National Weather Service said some sleet occurred at Dulles Airport on November 19.  That resulted in the first trace of sleet or snow at Dulles since April 9.

This November has been remarkably similar to last year’s.  Area residents may recall that November 2015 was also warmer than average, with a monthly average temperature of 53.7 degrees (4.1 degrees above average) and six days that saw temperatures of at least 70 degrees.  Also, this month has had five days with temperatures at or above 70 degrees in Washington, D.C.  The final ten days of November 2015 saw three days with high temperatures in the 40s, four in the 50s and days in the 60s.

Today is poised to feature high temperatures in the upper 40s with more seasonal temperatures expected in the 50s later in the week.  Fortunately for area residents this week will be mostly dry with only some showers possible late Wednesday night into Thursday.  That won’t help with the Mid-Atlantic’s drought conditions, but will limit any weather difficulties for Thanksgiving travelers.  You can rely on my colleagues and I on the WUSA9 weather team for the latest weather updates.

Drought Conditions Envelop the Mid-Atlantic

Washington, D.C. (November 2016)

Many Washingtonians have been enjoying the milder than average temperatures this fall.  However, this fall has been unusually dry in the Mid-Atlantic Region.  Although six of the first eight months of 2016 were drier than average in the Nation’s Capital, the lack of rain has gotten more noticeable since September 1.

Washington, D.C.’s annual rainfall deficit is 6.76” and most of that amount (5.29”) is just since September 1.  Following the record heat of July and August, the warm and dry weather this fall have acerbated the dry conditions.  This week’s updated Drought Monitor Index shows moderate drought conditions now exist from central Pennsylvania through central Maryland into parts of the District of Columbia and Virginia.

Recent freezing temperatures brought an end to the growing season for the Mid-Atlantic Region.  However, the growing rainfall deficit is ominous since no significant rainfall is expected over the next several days.  The deficit will continue to grow as NOAA expects only near to slightly above rainfall for the Mid-Atlantic Region during the rest of November.

Unlike late summer and early fall, the tropics tend to get much quieter in November so, area residents can’t count on significant rainfall from a decaying tropical system.  One exception was the summer of 1999, which was significantly hotter and drier than average.  However, September 1999 brought about an abrupt end to that summer’s dryness when record rainfall occurred in association with former Hurricanes Dennis and Floyd.  Although Hurricane Matthew brought copious rainfall totals from Florida to North Carolina last month, no appreciable rainfall occurred in the DC Metro Region.

The last time 0.5” or more of rainfall occurred in Washington, D.C. was on September 29 when 1.02” of rain fell.  However, since September saw only 2.5” of rain for the entire month (more than an inch below average) the growing rainfall deficit remains a problem.  My colleagues and I on the WUSA9 weather team will keep you apprised of the latest forecasts and weather updates.

Weather Quiz

On which holiday have Washingtonians seen more snow?

A.  Thanksgiving

B.  St. Patrick's Day

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Answer to Weather Quiz question from October 28.

Although both days can be warm or cold, Halloween does have higher average temperatures in Washington, D.C. (64/46) vs. St. Patrick’s Day (56/38).

Pacific Ocean Hurricanes

NOAA's Map of the 2016 Eastern Pacific Hurricane Season

As the end of hurricane season in the northeastern Pacific Ocean (off the west coast of Mexico) approaches on November 30, it's a good time to reflect upon how busy the season has been.  The eastern Pacific hurricane season starts two weeks earlier than the Atlantic hurricane season on May 15 but also runs through November 30.  It’s fitting that Tropical storm Tina dissipated yesterday off the west coast of the Mexico as the end of the season draws closer.

The National Hurricane Center says the eastern Pacific Ocean averages 15 tropical storms, 8 hurricanes and 4 major hurricanes.  This season there were 20 tropical storms of which 12 became hurricanes (6 major hurricanes) in the eastern Pacific Ocean.  That makes 2016 another busier than average eastern Pacific hurricane season.  Although Hurricane Newton impacted Baja California near the resort town of Cabo San Lucas in early September, it was not an especially damaging storm.

This season’s strongest eastern Pacific hurricane was Seymour, which peaked as a Category 4 with sustained winds of 150 mph last month.  That makes 2016 the first season since 2013 that no Category 5 hurricane developed in the eastern Pacific.  Despite not seeing any this season, the eastern Pacific Ocean has had Category 5 hurricanes in four of the last 7 seasons dating back to 2009. 

On the other hand, the Atlantic Ocean has not had a Category 5 hurricane since 2007 (prior to Hurricane Matthew earlier this fall).  Whether or not the hurricane season is more or less active than usual is irrelevant because a damaging or deadly storm can occur in any season.  A good example of that was the 1992 Atlantic hurricane season that was significantly quieter than average with only one major hurricane (Category 3 or higher).  However, that was Category 5 Hurricane Andrew, which remains one of the costliest natural disasters in U.S. history.

A key difference between the 2015 and 2016 hurricane seasons is that unlike a year ago, there is no major El Nino this year.  Last winter’s significant El Nino event helped create more favorable conditions for tropical storms and hurricanes in the eastern Pacific.  Meanwhile, that El Nino dissipated earlier this year and transitioned to an episode of La Nina.  NOAA says there’s a 55% chance that La Nina conditions will persist through the 2016-2017 winter season.  I will write about the Atlantic hurricane season closer to November 30 when it ends.