Halloween Weather

NOAA's October 31 Severe Weather Outlook

Rain on Halloween is a rarity in the Nation’s Capital.  Prior to today, measurable rainfall has occurred only twice on Halloween during the last 25 years, most recently in 2009.  Today’s rainfall will help push October 2019 toward the upper echelon of rainy Octobers in the Nation’s Capital.

As of yesterday, the Nation’s Capital had 5.41” of rain this month.  That’s despite having only 0.14” through October 15.  It’s also been an unusually warm month and is well positioned to finish among DC’s warmest October’s.  DC's average monthly temperature is 64.1° through October 30.  High temperatures this afternoon will reach well into the 70s. 

The unusually mild temperatures this Halloween won’t, however, approach record levels.  Today's record high for the Nation's Capital is 85° from 1950, while the record low is 26° which has occurred more than once, most recently in 1917.  The warmest Halloween in recent times was in 2004 when the high/low temperatures were 79°/59°, respectively, at National Airport.  Meanwhile, DC’s chilliest Halloween during the last 25 years occurred in 2002 with high/low temperatures of 47°/38°.

Not only will today feature much warmer than average temperatures, but NOAA's Storm Prediction Center also has a significant amount of the Mid-Atlantic Region under an enhanced risk of severe weather.  Scattered showers and thunderstorms are on tap this evening.  That will complicate Halloween activities, so it’s important for people to keep apprised of the latest weather conditions as the day wears on.

Although this Halloween’s weather has been atypical compared to the recent dry ones in the Nation’s Capital, it shouldn’t mask the fact that late October often features some of the nicest weather of the year in the Nation’s Capital.  DC’s average high/low temperatures on October 31 are 64°/46°, according to NOAA.

DC’s 10 Warmest Octobers (Source: NOAA)

1.  67.1° - 2007
2.  65.2° - 1984
3.  64.9° - 2017
4.  64.7° - 1971
5.  64.5° - 1947
6.  64.4° - 1941
7.  63.4° - 1949
8.  63.3° - 1973
9.  63.2° - 1975, 1919

---

DC’s 10 Wettest Octobers (Source: NOAA)

1.  9.41” – 2005
2.  8.81” – 1937

3.  8.69” – 1885
4.  8.65” – 1995

5.  8.33” – 1942
6.  7.76” – 1976

7.  7.40” – 1932
8.  6.76” – 1902
9.  6.55” – 2007
10.  6.50” – 1877

Late Season Tropical Storms

"Sandy" approaching the New Jersey coast, October 2012  (Source: NOAA)

Although the Atlantic hurricane season runs until November 30, the tropics see markedly less activity after October 15.  Only one major hurricane (Category 3 or higher) has impacted the United States on or after October 25 and that was the Category 3 Tampa Bay hurricane that made landfall on October 25, 1921.  Other significant systems have made landfall in the United States between October 15 and 31.

Sandy (2012):  Sandy was the strongest hurricane of the 2012 season, peaking as a Category 3 hurricane with sustained winds of 115 mph.  It tracked north after its landfall in Cuba at peak intensity.  Eventually, it made a northwesterly turn and made landfall as a weaker storm in New Jersey.  It caused extensive coastal flooding and had significant impacts that reached well inland.  Sandy also set a number of rainfall and low pressure records. 

Shortly before its landfall in New Jersey, it was determined that Sandy was no longer a tropical system.  In other words, it had lost its tropical characteristics over cooler ocean waters and was considered a non-tropical or “post-tropical” storm.  Consequently, all the hurricane watches and warnings were discontinued.  That led to a lot of confusion since many people thought the storm was no longer dangerous.  As a result of this controversy, it was determined that in the future hurricane watches and warnings should remain in effect even after a given storm becomes a non-tropical system.

Wilma (2005): - Before impacting the United States, Wilma became the strongest Atlantic hurricane on record with a minimum central air pressure of 882 millibars.  Its sustained winds also reached 185 mph, making it a Category 5 hurricane.  Fortunately, Wilma weakened significantly before it reached SW Florida where it made landfall October 24 as a Category 3 storm.  Wilma was also significant for being the last hurricane to make landfall anywhere in Florida until Hermine in 2016.

Hazel (1954): – Hazel remains the only Category 4 hurricane to make landfall in North Carolina (on October 15).  Due to Hazel’s fast rate of speed, it remained a powerful system well inland and brought Washington, D.C. its highest wind gust on record (98 mph).  It’s also worth noting that while North Carolina feels the impacts of tropical storms and hurricanes fairly often, no major hurricane (Category 3+) has made landfall there since Fran in 1996.

King (1950): King made landfall in Miami at approximately 1:00 AM on October 18.  It had sustained winds of 130 mph that made it a Category 4 hurricane.  It weakened rapidly as it tracked over Florida but, nevertheless, caused a lot of damage.  Florida was a relatively rural state at this time, so damage wasn’t what it would have been had a similar storm made landfall in recent times.

Tale of Two Extremes

Now in its final days, this October’s weather can be broken up into two distinct halves.  The month got off to a very dry start, but it will finish as DC’s first wetter than average October since 2014.  It will also finish as a warmer than average month.

Following a very dry August and September, and only 0.14” of rain during the first half of October, moderate to severe drought conditions enveloped the Nation’s Capital and its surrounding suburbs.  Fortunately, there was a dramatic shift in the weather pattern and the last two weeks were quite rainy in Washington, D.C.  A total of 1.6” of rain fell last Sunday, October 20, and that was DC’s largest daily rainfall since July 8.

Excluding today’s rainfall, Washingtonians have seen an impressive 3.53” of rain since October 16.  That’s gone a long way to reducing the intensity of the drought conditions in the Mid-Atlantic Region.  Despite a rainfall deficit of 5.93” for the period of August 1 – October 15, DC still has an overall rainfall surplus of 1.75” as of yesterday.  Given how wet last year was, it’s hard to fathom that his month has already been wetter than October 2018.

This month will also finish as DC’s fourth consecutive warmer than average October.  The two most significant temperatures in the Nation’s Capital this October are noteworthy for different reasons.  The high temperature of 98° on October 2 set a new record for DC’s hottest October temperature.  Meanwhile, the high temperature of only 58° last Sunday – that coincided with the 1.6” of rain – was DC’s chilliest day in more than six months.  Prior to October 20, the last time DC’s high temperature remained below 60° was April 5, 2019 (56°).

Some may wonder whether a correlation exists between a warmer and wetter than average October in the Nation’s Capital and a colder and snowier than average winter.  The short answer is no, but there are some interesting parallels.  October was a cooler and wetter than average month in 2002 and 2009, and it was followed by two of DC’s snowiest winters on record during moderate episodes of El Nino.  On the other hand, October 1995 was a warmer and wetter than average month and the 1995-1996 winter was also quite snowy during a moderate episode of La Nina. 

Forecasting winter weather is quite complex and there are many factors involved.  Simple autumn temperature and rainfall trends aren’t enough to draw conclusions from.  My colleagues and I on the WUSA9 weather team will issue our winter weather outlook soon.