Weather Quiz

True or False.  Today’s record low temperature of -4° that occurred 25 years ago in 1994 was DC’s last temperature at or below 0°.

Winter Weather Averages

January 13, 2018 in Bethesda, Maryland

The DC Metro Area had its ninth largest January snowfall on record this past weekend with 10.3” at National Airport.  The snow fell for an unusually long period of time at National Airport: 35 consecutive hours from 3:00 Saturday afternoon, January 12, to 2:00 Monday morning, January 14.  It was the DC Area’s largest overall snow event since the record January 2016 storm.

Temperature and precipitation averages are kept by the National Weather Service and are updated every 10 years.  DC’s current annual snowfall average of 15.4” is based on the 30-year period from 1981 through 2010.  While the Nation’s Capital had 10 snowier than average January’s between 1981 and 2010, there have been only two since 2011.  However, January 2019 also became a snowier than average month in Washington, D.C. with this past weekend’s storm.

There are a few more chances to add to DC’s snow total in the next few days.  The month of January is DC’s second snowiest month of the year with an average of 5.6”, narrowly behind February’s 5.7”.  Three of DC’s 10 largest snowstorms occurred in January, while six occurred in February.  Also, five of DC’s 10 largest snowstorms have occurred relatively recently in the last 23 years since the January 1996 blizzard.

Something a lot less frequent in recent decades has been record cold.  The Nation’s Capital hasn’t set a record low temperature in January in nearly 25 years, since it was -4° on January 19, 1994.  Temperatures have only fallen to the single digits in Washington, D.C. four times in January during the last 20 years.  Washingtonians did set a record low of 5° on February 20, 2015, and that was DC’s first record low in February since 1970.

DC’s official weather measurements have been made at National Airport since 1942.  As urbanization has increased, there has been a commensurate increase in the urban heat island effect.  That means it’s a lot harder for temperatures to fall to levels seen decades ago when there was less development and urbanization.  By comparison, Dulles Airport, in the more rural Sterling, VA, has been below 0° as recently as last winter (-1° on January 7, 2018) and has set multiple record low temperatures over the last five winters.

This coming Monday, January 21, is poised to be DC’s coldest day of the winter season so far with high temperatures only around 20°.  That’s less than half the daily average high temperature of 43°.

Last Time High Temperatures Below 30°

Washington, D.C. (National Airport – DCA): 28° (January 14, 2018)
Dulles Airport, Sterling, VA (IAD): 26° (January 14, 2018)
Baltimore, MD (BWI Airport): 27° (January 14, 2018)

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Last Time High Temperatures Below 20°

DCA: 19° (January 22, 2014)
IAD: 19° (January 6, 2018)
BWI: 18° (January 6, 2018)

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Last Time Low Temperatures </=10°

DCA: 8° (January 7, 2018)
IAD: 9° (January 15, 2018)
BWI: 1° (January 7, 2018)

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Last Time Below 0°

DCA: -4° (January 19, 1994)
IAD: -1° (January 7, 2018)
BWI: -1° (February 5, 1996)

What a Snowstorm !

Germantown, Maryland  (Courtesy: Susan Granzow)

The sun has come out in the nation’s capital after its largest snowstorm in nearly three years.  This was a long-lasting storm that spanned 35 hours over three days with snow reported at National Airport from 3 PM Saturday afternoon, January 12, to 2 AM Monday, January 14.  Fortunately, the storm occurred over the weekend when the volume of road traffic was lighter and that allowed road crews to work more efficiently.

The January 2019 snowstorm was impressive for a variety of reasons.  It was DC’s third largest January snowstorm in the last 30 years, behind only the January 1996 and 2016 storms.  It produced daily snowfall records on January 13 at both National and Dulles Airports.  If you include the 1.4” of snow that Washingtonians got on November 15, 2018, then DC’s seasonal snow total so far for the 2018-2019 winter (11.7”) is more than the last two winters (2016-2017 and 2017-2018) combined (11.2”).

November 2018 was colder than average and DC’s snowiest November since 1989.  December 2018 and the first 10 days of January were considerably warmer than average with no snow.  With a dramatic shift in the weather pattern, DC Area residents are in a more-typical winter-like weather with near to slightly below average temperatures for the upcoming work-week.  

It’s worth emphasizing the remarkable job that DC Area meteorologists did forecasting this event for the entire week leading up to this past weekend’s winter storm.  Initial calls for snow came last weekend from my colleagues and I on the WUSA9 Weather Team, as well as other local meteorologists.  The forecast was updated throughout last week, so no one should have been surprised that it snowed over the weekend.

Some people expressed surprise that snow totals reached double-digits in many areas of the DC Metro Area.  It’s true there was some fluctuation in the forecast of snow accumulation during the week while the storm was over 1,000 miles away, but as the event drew closer and more snow was expected the forecast was updated commensurately.  Forecasted snow accumulations were increased twice – the day before the snow began on Friday night and again on Saturday.

Forecasting winter weather requires a high degree of skill.  The independent variables involved in forecasting winter weather such as storm track and amount of cold air (that influences precipitation type) illustrate the challenge in winter weather forecasting.  It’s vital for people to stay informed to the latest weather forecast since the potential for more changes exists as a winter storm draws closer.  Even subtle changes in storm track can make a big difference in both precipitation type and amounts.

Storm Totals (According to the National Weather Service)

Washington, D.C. (National Airport, “DCA”):

January 12: 1.9”
January 13: 8.3” (New Daily Record)
January 14: 0.1”

For a 3-day storm total of 10.3”

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Dulles Airport (“IAD”), Sterling, Virginia:

January 12: 2.9”
January 13: 7.7” (New Daily Record)

For a storm total of 10.6”

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Baltimore, Maryland (BWI Airport):

January 12: 1.8”
January 13: 4.8”

For a storm total of 6.6”

DC’s First Winter Storm of 2019

WUSA9's "Final Call" Snow Forecast Map

DC’s storm this weekend is likely to be its most significant winter storm since January 2016.  That’s when Washingtonians experienced the fourth largest snowstorm on record.  However, unlike three years ago this storm won’t be record setting by any stretch.

The last two January’s had significantly below average snowfall in Washington, D.C. with 1.4” in January 2017 and 1.2” last January.  By comparison, January 2016 had a total of 18.8”, the bulk of which occurred during the “Blizzard of 2016” (17.8”).  The Nation’s Capital averages 5.7” of snow in January, according to NOAA.  It’s worth noting that this weekend’s snowfall will also be DC’s first measurable snowfall since 1.4” accumulated on November 15, 2018.

The weather setup for this storm is traditional in the sense that the Mid-Atlantic Region transitioned to a colder air mass two days prior to the storm’s arrival in the eastern United States.  An area of high pressure located in the northeastern United States has allowed a sufficient amount of cold air to filter into the DC Metro Area.  That will keep the precipitation predominantly snow from the immediate DC Metro Area to points west.  Although the current storm we’re watching began to take shape in the southwestern United States, as opposed to developing along the southeast or Gulf Coasts, the track will be adequate to bring enough moisture to the Nation’s Capital for snow to occur. 

Consequently, Washingtonians are in for a respectable January snowstorm with several inches of snow expected.  That should put Washington, D.C. near January’s monthly snowfall average.  That’s something which has occurred during only seven of the last 20 January’s dating back to 1999.  However, January 2016 was DC’s eighth snowiest on record.

The overall weather pattern so far this winter (2018-2019) has been similar to the 2015-2016 one that featured DC’s warmest December on record, as well as a mild start to January.  January 2016 had a significant shift in the weather pattern in the middle of the month that gave way to a cold and snowy second half.  December 2015 and December 2018 were both two of only three Decembers during the last 20 years when Washington, D.C. had no snow whatsoever.  Whether or not this winter ends up being snowier than average like the 2015-2016 remains to be seen.  Regardless, this weekend’s winter storm should please DC Area snow-lovers without causing the consternation that winter precipitation invariably causes commuters during the workweek.

Last time 1”/+ of January snow occurred at:

Washington, D.C., National Airport (DCA): 1” (January 30, 2017)
Dulles Airport, Sterling, Virginia (IAD): 22.1” (January 23, 2016)
Baltimore, Maryland, BWI Airport (BWI): 1.3” (January 17, 2018)

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Last time 5”/+ of January snow occurred at:

DCA: January 23, 2016 (11.5”)
IAD: January 23, 2016 (22.1”)
BWI: January 23, 2016 (25.5”)

DC’s Second Snowiest Month ?

The Nation’s Capital is colder than average today for the first time since December 12.  Temperatures this morning fell below freezing for the first time since December 26.  Winter weather enthusiasts should be pleased with this change in the weather pattern from to typical mid-January weather.  While not unusually cold, the weather over the next few days will only feel especially cold because of how mild it has been: the first nine days of January finished 10.3° above average.

Sufficiently cold temperatures are obviously one of the two major ingredients for snow – along with a storm that brings precipitation.  DC Area meteorologists, like my colleagues and I on the WUSA9 Weather Team, are watching the latest model runs as the first winter storm of 2019 in the Mid-Atlantic Region draws closer this weekend.  January is DC’s second snowiest month with an average of 5.6” (February averages 5.7”).  The last time Washingtonians had an inch or more of snow in January was on January 30, 2017 (1”).

November 2018 finished 3.1° colder than average in the Nation’s Capital and saw DC’s most significant snowfall since 1989.  By comparison, December 2018 finished 3.8° and became only the third December in the last 20 years without any snowfall.  This was the first time since 1983 that Washington, D.C. had accumulating snow in November with no measurable snowfall in December.

Going from a milder than average December 2018 and start to January to a more winter-like pattern is quite common.  As recently as the 2015-2016 winter season, Washingtonians experienced a huge swing between DC’s warmest December on record and the belated arrival of winter.  The 2015-2016 winter season also set a record for the latest in the season that the first measurable snowfall occurred in Washington, D.C. (i.e., 0.3” fell at National Airport on January 17, 2016).  That was nearly two months later than the first snow of the 2018-2019 winter season that occurred on November 15, 2018.  

This weekend’s storm is hardly going to be a record-setting storm, unlike what occurred in January 2016.  The epic January 2016 storm helped make it DC’s snowiest January (18.8”) since 1996.  That would have been hard to envision considering the very mild six-week period from December 1, 2015 through January 10, 2016.  

The six-week period from December 1, 2018 to January 9, 2019 was also largely warmer than average.  This serves to illustrate that snow and cold can occur relatively quickly after an extended period of winter warmth in the DC Metro Area.  Snow lovers shouldn’t fret that this weekend’s anticipated storm isn’t expected to be a record-setter because accumulating snow can occur well into March.  For example, the month of March was DC’s snowiest month of the winter season during the 2012-2013, 2013-2014 and 2017-2018 winter seasons.

One Extreme to the Other

January 2019 has gotten off to a mild start in Washington, D.C.

The start to 2019 couldn’t be more different than the way 2018 began.  Last January got underway in the midst of a frigid 12-day period with temperatures at or below 35° from December 27, 2017 – January 7, 2018.  Meanwhile, the first six days of 2019 were significantly warmer than average.  The high/low temperatures on January 6, 2018 were 21°/11°, compared to January 6, 2019 with 57°/39°.

Four of the last five January’s were colder than average in Washington, D.C.  In that time, three of the last five January’s also featured below average snowfall.  The exception was in January 2016 when Washingtonians experienced their fourth largest snowstorm on record.  It was also DC’s second largest January snowstorm behind only the 1922 “Knickerbocker Storm.”  

This winter has been a disappointment thus far for DC-Area snow lovers.  Following DC’s most significant November snowfall since 1989 less than two months ago, no snow has fallen since December 1.  In fact, December 2018 finished as DC’s eighteenth warmest dating back to 1871 and was only the third December in the last 20 years to finish without any snowfall.

However, that should not create consternation among area snow lovers.  Two winters in the last five years had significantly warmer than average Decembers, but were followed by colder and snowier than average January’s.  While December 2013 finished 2.6° warmer than average in Washington, D.C., January 2014 finished 3.5° colder than average along with above average monthly snowfall.  Only two years later, Washingtonians experienced the warmest December on record in 2015 (11.5° warmer than average) with no snowfall.  Then January 2016 finished 1.1° colder than average with DC’s fourth largest snowfall on record.

Longtime Washingtonians and local weather enthusiasts know that the right ingredients only need to come together once to produce an epic snowfall.  Colder than average temperatures are on tap later this week in the Nation’s Capital.  Because accurately forecasting winter weather requires a high degree of skill and experience, it’s important to rely on reputable sources for your weather forecasts, like my colleagues and I on the WUSA9 Weather Team.

2019 Picks Up Where 2018 Left Off

DC had a fitting end to 2018 with a warmer and wetter than average December.  Last month finished 3.8° warmer than average for the seventh time in the last eight years.  A total of 5.82” of rain also occurred in DC last month, which made for DC’s eighth wettest December on record.  2018 finished with 66.28” of rain – DC’s wettest year on record!

January 2019 has gotten off to a similar start, with above average temperatures and forecasts of rain in the DC Metro Area.  Average January temperatures in Washington, D.C. feature a high/low of 44°/29° on January 1.  DC’s warmest January temperature on record is 79° on January 26, 1950.  Although uncommon, temperatures in the 70s occur much more frequently in the Nation’s Capital during the month of January compared to subzero temperatures.  The last time DC had a January high temperature in the 70s was on January 6, 2017 (73°).

Meanwhile the coldest January temperature observed in the Nation’s Capital is -14° on January 1, 1881.  DC’s coldest January temperature at National Airport is -5° on January 17, 1982.  The last time Washingtonians experienced a below 0 temperature was on January 19, 1994 (-4°). Eleven of the last 20 January’s have been colder than average in DC, including four of the last five.  Area residents should recall the frigid start to 2018 with high temperatures in the 20s on six of the first seven days.

The month of January averages 2.81” of rain in Washington, D.C. (that includes 5.6” of snow).  However, 15 of the last 20 January’s have been drier than average in the Nation’s Capital, including the last three.  It’s possible to have a drier than average month, and still have a snowier than average month.  For example, January 2016 finished with 2.68” of rain (that includes liquid snow equivalent), but a record snowstorm occurred on January 22-23, 2016 when a total of 17.8” fell (DC’s fourth largest snowfall).  That’s possible when a dry snow occurs.  

When temperatures are near freezing, the atmosphere can hold additional water vapor leading to snow that has a higher moisture content.  The colder the temperatures are, the lighter and drier the snowfall tends to be.  NOAA expects the warmer than average temperatures with near average precipitation to continue in the DC Metro Area through the middle of January.