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Posted at 11:42 AM ET, 12/16/2011

What is Washington, D.C.’s weather like in December? Breaking down norms and extremes


December 5, 2007 — One of a series of recent December 5 snowfalls. This event dropped 2.6” of snow at National Airport. Photo by author. See image larger.
Winter is here, especially if you follow the meteorological calendar which defines it as December through February. Whether you believe the season starts on the 1st of this month, or you follow the astronomical calendar which brings it along during the final third, the month heralds the start of the coldest time of year.

It’s the wettest month of the meteorological winter months as well. When it comes to whitest, it’s third of the three. But while the first half in particular is still thought of as “early season,” big snow events are possible, and some memorable ones have hit.

Keep reading for more in this ninth installment of a year-long series of posts detailing specific statistics on climate norms, extremes, and averages for the each month in Washington, D.C…

PRECIPITATION

The 1981-2010 average* total precipitation for December is 3.05”, this is a change of 0.00” from previous norms as measured from 1971-2000. It’s the only month of the year with no change in raw precipitation (rain and snow) averages of the year, owing at least in part to its relative stability in extreme precipitation — a commonality in all winter months, at least compared to summer.


Monthly rainfall (in inches) in Washington, D.C. from 1871-2010. See sources for data.

The wettest December on record came in 1901 with 7.56”. 2009 is a not-to-distant second with 6.79”. A total of five Decembers have seen precipitation totals of 6.00” or greater. When it comes to the driest December we’ve seen, it was a measly 0.19” back in 1889.

The most rain that has fallen in one day during the month fell earlier this month — December 7, 2011 when 3.10” of rain fell at Reagan National Airport, also the meteorological winter and Nov-Mar record rainfall. Only eight days in December have seen more than 2” of rain, way down from the summer months and the water content of the tropical air masses they contain.


Monthly snowfall (in inches) in Washington, D.C. from 1888-2010. See sources for data.

Even though snow is still generally much less significant than the latter months of meteorological winter (Feb and Jan), it’s still always on the minds of many around the area. Snow lovers can rejoice in the fact that December’s snow totals increased for the 1981-2010 norms compared to 1971-2000 normals (the only cold season month to do so). The 1981-2010 normal of 2.3” for the month is up 0.8” from the tiny 1.5” normal of old (thanks largely to some snowy Decembers in the last decade).

There have been about 180 events with accumulating snow during D.C.’s snow history going back to 1888, or generally between 15-20% of all events in any month throughout history. A significant majority of these events have come with rain for much of the storm, and around 30% have been able to produce 3” or more (though potentially finishing with less or even no snow on the ground depending on the evolution of precipitation).


The top ten accumulation events in December at Washington, D.C. Numbers are in inches of snowfall. * NWS Baltimore/Washington lists this (Dec 17, 1932) as a 12" storm but daily records indicate it was 11.5".

December’s top events range from 16.4” in 2009 to 7.0” in 1904 and 1966 (not shown above). The 16.4” in 2009, including a record for any December day 15” on the 19th, came over two days in a storm dubbed “Snowpocalypse” during the opening salvo of the intensely snowy winter of 2009-10.

Another December record held by that year is the 16” of snow measured on the ground (i.e. snow cover) at National (though many places had more of course). Through 2010, there have been a total of 309 December days with snow cover of greater than 1”, or about 18% of all days in the month throughout the historical period.

TEMPERATURES


December temperature averages throughout recorded history (in degrees F) at Washington, D.C. See sources for data.

While it’s considerably less snowy than the later winter months of January and February, winter chill does set in with the monthly average temperature just below 40 degrees, not to return above 40 until March. The normal of 39.7 degrees represents just a 0.2” change from the old norms, which is the smallest increase of any month. Consider yourself generally lucky (depending on your perspective) once we get past the first few days if you don’t have to grab a coat when going out.

It is of course getting colder day by day! The average daily high temperature falls from 52 degrees at the start of the month to 45 degrees at its finish. Daily average lows dip below freezing as well, starting the month at 37 degrees and finishing at 29 degrees. When we hit the 16th , we can “expect” to drop to at least freezing in the overnight as this is when norms touch 32 degrees.


Raw (non smoothed) odds of a low temperature 32 degrees (freezing) or below at Washington, D.C., by day of the month. Both long-term and recent trends exhibit a similar pattern overall. See sources for data.

Looking at 1981-2010 as a guide, high temperatures in the 40s are most common at 39%. with 50s holding 28%, 30s 18%, 60s 8%, and 20s, 70s and teens making up the final portion of the pie. Nearly half of lows were in the 30s at 49%. Next up were 20s at 28% of the time, 40s 15%, and 10s, 50s and single digits compiling the rest.

It’s never been in the 80s in December in Washington. The warmest temperature on record for the month is the 79 degrees witnessed on the balmy 7th of 1998. When it comes to the coldest maximum temperature, it is the 9 degree readings of the 30th, both in 1880 and 1917. At National, the coldest daytime high is 14 on Christmas Day in 1983.

When talking low temperatures, the warmest low on record for December is the 59 degrees on the 5th in 1973. And if you’re talking the coldest low temperature for the month, you’re talking brutal cold. It was an incredible -13 on the 31st way back in 1880. Only three days in December have seen sub-zero temperatures and the coldest it’s been at National was 3, on the same Christmas day as the coldest maximum high noted above.

DATA

30-year (1981-2010) Averages / Overall (all history) Averages...

Highs below 50: 19.2 / 20.7
Highs below 40: 6.9 / 8.9
Highs 32 or less: 2.0 / 2.9
Highs 60 or above: 3.3 / 3.1
Lows below 40: 25.5 / 26.7
Lows 32 or less: 15.2 / 18.1
Days with at least a trace of rain: 13.8/ 13.7
Days with .1” of rain or more: 5.6 / 5.8
Days with .5” of rain or more: 2.4 / 2.3
Days with 1” of rain or more: 0.5 / 0.7

Days with at least a trace of snow: 4.3 / 4.6
Days with 1” of snow or more: 0.7 / 0.9

Days with thunder: 0.1 / NA
Days with hail: 0.0 / NA
-This count is done through records on Weather Underground, and does not include the entire historical period.

All-Time Records (High / Low)...

Highs below 50: 30 (1903, 1917) / 7 (1899)
Highs below 40: 23 (1876) / 5 (5 years)
Highs 32 or less: 15 (1876) / 0 (38 years)
Highs 60 or above: 10 (1932, 1951, 1971) / 0 (23 years)
Lows below 40: 31 (16 years) / 16 (2001)
Lows 32 or less: 30 (1904, 1910) / 7 (4 years)
Days with at least a trace of rain: 21 (1906, 1935) / 7 (4 years)
Days with .1” of rain or more: 11 (1945, 2007, 2009) / 0 (1899, 1955)
Days with .5” of rain or more: 6 (4 years) / 0 (13 years)
Days with 1” of rain or more: 3 (6 years) / 0 (71 years)

Days with at least a trace of snow: 13 (1935, 1969) /
Days with 1” of snow or more: 4 (5 years) /

Days with thunder: 2 (2004) / 0 (27 years)
-Same as above. (30-year high / low listed)

SOURCES

Daily climate records for Washington, D.C., 1871-present
- See selected and additional statistics compiled for this post (Excel)

D.C. climate norms 1981-2010

D.C. December daily norms and records

D.C. monthly temperatures

D.C. monthly precipitation

NWS Baltimore/Washington climate information

NOTES

*All averages or normals, unless otherwise noted, refer to the 30-year period of 1981-2010. Unlike initial months, a full set of new climate norms is now available and will be used throughout. Past months will be edited to reflect the new norms.

ABOUT THIS SERIES

While numerous local climatology statistics including daily, monthly, and seasonal normals and records are available from National Weather Service Baltimore/Washington, there are myriad other pieces of information which help frame the story. Rather than attempt to recreate what is already available, this series of posts will act as a companion to most information presented there.

This is the ninth installment of a series of living documents. Through early 2012, each month will be broken down in a similar or evolving way. As input is taken from the community, some items may be added to or changed in older postings. These postings will be updated as necessary to reflect changes when needed. Other articles may also become part of this series.

Feel free to share thoughts or additional data you may be interested in seeing.

Learn more about each month:

-April weather in Washington, D.C.
-May weather in Washington, D.C.
-June weather in Washington, D.C.
-July weather in Washington, D.C.
-August weather in Washington, D.C.
-September weather in Washington, D.C.
-October weather in Washington, D.C.
-November weather in Washington, D.C.
-December weather in Washington, D.C. (viewing)

Article last updated: December 16, 2011.

By  |  11:42 AM ET, 12/16/2011

Categories:  Local Climate, Latest

 
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