How Impressive have January’s Storms been in DC ?

The two major ingredients required for a significant snow event are a sufficient amount of cold air combined with the ideal track of a moisture-laden storm.  This weekend’s storm produced a lot of rain in the DC Metro Region since one of the two major ingredients were in place.  However, the storm track was such that Washingtonians were on the warm side of the storm.  This morning’s high temperature climbed to a March-like 56° before the cold air began to envelop the DC area.

The ideal storm track would take the center of low pressure along the Carolina coast far north as roughly the Norfolk, Virginia area.  That would allow the requisite area of cold Canadian high pressure to hold enough cold air in place as the moisture began to fall in the form of snow in the DC area.  If the area of low pressure tracks too far north or west, then the column of cold air erodes leading to a wintry mix or just rain.

Nearly three years have passed since DC residents experienced one of the largest winter storms on record.  The Blizzard of 2016 occurred on January 22-23, 2016 and had the ideal storm track to produce record snowfall in the Nation’s Capital.  This weekend’s storm couldn’t have been more different.  The way this storm tracked put the DC Metro Area in the warm sector of the storm, keeping the precipitation predominantly rain (in some areas well north and west of DC such as Frederick and Washington Counties in Maryland the rain began as some snow).

The rain began late yesterday afternoon and continued until early this morning in Washington, D.C.  The Nation’s Capital had 0.8” by the time it tapered off before dawn today.  That was DC’s largest January two-day rainfall total since January 2-3, 2017 (1.21”).  By comparison, there was plenty of cold air in place last weekend when DC had 10.2” of snow, or the liquid equivalent of 0.84”.  If there was adequate cold air in place for this weekend’s storm, then Washingtonians could have potentially had two 10” snowfalls within a week.

Only two months in the last 20 years have had 20”/+ snow (February 2003 and February 2010).  The last time DC residents experienced 20”/+ snow during the month of January was in 1996.  DC Area snow-lovers shouldn’t be discouraged that this weekend’s storm was predominantly rain.  Washington, D.C. has already had 12.7” of snow since November 1, 2018, which is more than 80% of DC’s seasonal snowfall average of 15.4”. 

NOAA expects below average temperatures to continue for the rest of January.  That’s in conjunction with a 33% probability for above average precipitation for the DC Metro Area.  The ideal circumstances for a significant snow event (5”/+) in the Nation’s Capital don’t come together often.  However, if they come together just once, then the entire winter season could finish snowier than average.

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”)