Halloween: DC’s Scariest Weather of the Year?

 

October 2020 has been a memorable weather month in the Nation’s Capital.  Although it will finish warmer than average, today has been quite chilly with highs only around 50°.  That’s more characteristic of early December than late October.  Halloween will be cold this evening with temperatures in the 40s.

Through October 30, DC’s average monthly temperature (combining daily high and low temperatures) is 62.4° (2.8° above average), making this DC’s fifth consecutive warmer than average October.  The last time the Nation’s Capital experienced that kind of streak was 1982 – 1986.  Although no 90° heat occurred this October, there were two days with highs in the 80s.  In fact, DC’s high temperature of 80° on October 22 was the latest 80° temperature in the Nation’s Capital during October since 2014.  

The DC Metro Area also had a wetter than average month largely due to the remnants of two tropical systems.  The remnants of Hurricane Delta brought a two-day total of 1.54” of rain on October 11-12.  Meanwhile, the combination of ex-Hurricane Zeta and a cold front brought 2.57” of rain on October 29-30.  There has been a total of 4.86” of rain at National Airport since October 1, making October 2020 the second straight wetter than average October.  However, if you subtract the rain from the former tropical systems, this would have been a dry month with only 0.75” of rain compared to DC’s October average of 3.40”. 

Some may wonder what Halloween weather is like historically in the Nation’s Capital.  Last year couldn’t have been more different than this year, with a high/low of 77°/53°.  It was also a wet Halloween last year with 1.25” of rain.  DC’s average high/low temperatures on October 31 are 64°/46°.  That’s compared to DC’s record October 31 high of 85° from 1950.  Meanwhile, today’s record low is 26°, which last occurred in 1917. 

Over the last 25 years, DC has had measurable rainfall on only two Halloweens: 2002 and 2009.  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 over the last 25 years occurred in 2002 with high/low temperatures of 47°/38°.  Today’s temperatures will be close to the cold Halloween Washingtonians experienced in 2002.  Fortunately, for those who don’t like the cooler than average weather, a warm-up will occur later next week.

Hurricane Sandy vs. Zeta

 

Saffir-Simpson Hurricane Scale (Courtesy: WUSA9)

It’s ironic that the DC Metro Area is experiencing such a rainy and raw day today with the remnants of Hurricane Zeta.  That’s because it was on October 29 eight years ago that the Mid-Atlantic Region experienced a record-setting event due to former Hurricane Sandy.  Daily rainfall records were set at all three DC Area Airports during Sandy and the name was subsequently retired for being destructive and deadly.

While Zeta hasn’t had the same impacts, it came during the 2020 hurricane season that’s been more active than the 2012 season was.  While Hurricane Sandy was a Category 3 hurricane at peak intensity and the strongest Atlantic hurricane of 2012, it was a weaker system when it made landfall.  Zeta made landfall in Louisiana close to 6:00 p.m. as a strong Category 2 hurricane with sustained winds of 110 mph - just under Category 3 status on the Saffir-Simpson Hurricane Scale.

Similar to Hurricane Michael two years ago, Zeta intensified right up until it made landfall.  There's a good chance Zeta would have reached Category 3 intensity had it remained over the Gulf a little longer.  The differences on the ground, however, between a strong Category 2 and a low-end 3 are relatively minor. 

Sandy was an entirely different story as it tracked northward in the Atlantic Ocean in late October, where the environmental and atmospheric conditions were much less favorable for a tropical system.  Shortly before Sandy made landfall, the National Hurricane Center declared it a non-tropical or post-tropical storm.  Consequently, all the tropical storm watches and warnings that had been in effect along the Mid-Atlantic and northeast coasts were dropped.  That contributed to the illusion among the general public that Sandy was no longer a serious threat.  That couldn't have been a larger misconception as Sandy became one of the costliest natural disasters in U.S. history.  There are parts of New York and New Jersey that still haven't fully recovered eight years later.

Both Hurricanes Zeta and Sandy illustrate that significant hurricanes can occur in late-October and have serious impacts in the United States.  They're just less common than earlier in the season.  

October 29 Daily Rainfall Records - All from 2012 courtesy of "Sandy"

Washington, D.C. (National Airport): 3.85" 

Dulles Airport, Sterling, Virginia: 4.25" (Monthly record)
Baltimore, Maryland (BWI Airport): 5.51" (Monthly record)

Looking Ahead to Winter

 

Despite yesterday with a high of only 57°, October 2020 is well-positioned to finish as a warmer than average month.  Average monthly temperatures (combining daily high and low temperatures) in the Nation’s Capital were 3° warmer than average through October 24.  By comparison, yesterday’s weather felt especially cold following a five-day stretch temperatures that were at least 10° warmer than average.

Average high temperatures during the month of October range from 74° at the start of the month to 64° on Halloween.  Meanwhile, temperatures during the day yesterday remained in the mid to upper 40s with light rain and drizzle that made it feel more like a late November day.  However, that shouldn’t prevent this month from finishing well above average.  There is also the prospect of heavier rain later in the week in the DC Metro Area with the remnants of Tropical Storm Zeta. 

Some may wonder if a warmer than average October combined with La Nina conditions is a reliable indicator of what the upcoming winter season will be like.  The short answer is no, but there are some exceptions.  For example, October 2017 was DC’s third warmest on record and the 2017-2018 winter season had a weak episode of La Nina.  La Nina winters are often warmer than average, with near average precipitation in the Nation’s Capital.  The 2017-2018 winter season as a whole (December 1 – February 28) was 1.9° milder than average.  Only 7.8” of snow occurred – or approximately half of DC’s seasonal average of 15.4”.

Conversely, DC’s warmest October occurred in 2007 and the 2007-2008 winter featured a strong episode of La Nina.  Consequently, the Nation’s Capital had less than a third of the seasonal average with only 4.9” of snow.  That winter was also 2.7° warmer than average.

NOAA’s Climate Prediction Center says there’s an 85% chance La Nina conditions will continue through the 2020-2021 winter season.  That doesn’t bode well for winter weather enthusiasts in the DC Metro Area.  However, they shouldn’t give up hope for snow this winter – certainly more than the 0.6” that occurred all of last winter.  Even in a warmer than average winter, the right ingredients only need to come together once to produce a significant snow event in the Nation’s Capital.