Ice is seen on the Tidal Basin after a cold spell in early February 2009. Photo by CWG photographer Kevin Ambrose.
As the first impressive Arctic air mass of the season settles in to Washington, D.C., we’re reminded that truly cold air does visit the area regularly despite last year’s general no show.
Even in Washington’s warmest of years, the city almost never escapes days of highs below freezing at least once or twice. Reality often means quite a bit more than that.
In its coldest years, what sometimes seems like ages ago, temperatures have even been known to dip below zero. During the 2000s, D.C. has seen readings as low as the single digits and highs only making the teens.
Though the climate record goes back to the 1800s, since around the time of the station switch to National Airport the coldest of the cold temperatures have seemingly vanished.
For instance, 19 years prior to the switch in 1945 had “coldest lows” of zero or less. At National Airport, lows have dipped below zero in only three years.
The coldest highs and coldest lows by year since 1946, the first full year of data observed at National Airport.
Since the mid-1940s, 64 percent of years had their coldest high temperatures in January, with February second-most favored at 20 percent and December the next likely. 61 percent of the coldest lows occurred in the month of January.
The coldest high temperatures recorded at National by year have most often been in the 20s and low 30s. The coldest lows for a year have typically fallen into the teens and single digits.
National has dipped as low as -5 degrees, which happened back on January 17, 1982. In the full climate history for D.C., the coldest reading was -15 degrees on February 11, 1899.
Setting the stage for that all-time cold temperature, Washington’s coldest high on record is a numbing 4 degrees on February 10, 1899. At National Airport it has been as chilly as 8 degrees on January 19, 1994.
Only one year has featured a day without a high at or below freezing. It occurred in 1974, when the coldest high temperature was a balmy 33 degrees on January 13. Last year wasn’t far behind with only one day reaching 32 degrees.
Days with highs at or below freezing by cold season. The season with the most is 1917-18 with 37. The season with the most at National Airport is 1960-61 with 21. 1997-98 is the only season without any days in this category, and 2011-12 joined two other years with one.
Looking at winters inclusive of 1980-81 through 2009-10, done to match the current climatological normals, it’s apparent that even the mildest parts of urban Washington should expect a sizable chunk of frozen days each winter.
The recent average for days at or below freezing comes out to nine per cold season. When lowering the maximum temperature bar to 25 degrees or less, the city should still expect about two per winter season.
Using the same 30 cold seasons, D.C. averages 65 days of low temperatures below freezing, 25 days with lows 25 degrees or below, and 12 days of readings 20 degrees or below.
When you get down to the really cold temperatures, or those 10 degrees and below, we’ve seen them as recently as the winters of 2008-09, 2006-07 and 2003-04. The instances of this level cold have not been numerous of late, but as recently as 1993-94 there were six days with lows of 10 degrees or lower.
Streaks of cold weather, as in consecutive days without surpassing freezing, are another good indicator of how impressive an Arctic blast may be when compared to others. For the most part, the immediate D.C. area does not experience super-lengthy stretches of this type of weather.
Number of streaks (two days in a row or more) of highs freezing or below at National Airport (left axis). In the period shown, the most streaks in a season is five in four separate years. The longest streak (shown on the right axis) was 10 days in 1989-90.
Yet, about 80 percent of recent winters have accomplished back-to-back (or more) days at or below the freezing high temperature threshold.
Since the winter of 1999-2000, including all winter months in the 2000s, D.C. has averaged about two such freezing stretches per cold season.
When it comes to length of frozen temperatures, that same period would suggest most stretches that make it to two days last between two and three days. Winter 2006-07 was able to top out at four days in a row, and winter 2003-04 got to six.
Interestingly, some of the most intense Arctic attacks of recent did not feature the lengthiest period of below freezing streaks. 1984-1985’s max was three days and 1993-94’s max was five.
The longest sub-freezing stretch since 1980 occurred December 16-25, 1989 - it lasted 10 days. Other notably cold periods like that of January 1977 featured patches of shorter streaks with small breaks in between.
LAST OCCURRENCE STATS (as of day prior to post)
High...
32 or below... Jan 22, 2012 (32 degrees)
30 or below... Jan 22, 2011 (28 degrees)
25 or below... Jan 30, 2010 (23 degrees)
20 or below... Jan 16, 2009 (18 degrees)
15 or below... Jan 19, 1994 (8 degrees)
5 or below... Feb 10, 1899 (4 degrees)
Low...
20 or below... Jan 4, 2012 (17 degrees)
15 or below... Mar 3, 2009 (14 degrees)
10 or below... Jan 17, 2009 (8 degrees)
5 or below... Feb 5, 1996 (5 degrees)
0 or below... Jan 19, 1994 (-4 degrees)
-5 or below... Jan 17, 1982 (-5 degrees)
-10 or below... Jan 14, 1912 (-13 degrees)
-15 or below... Feb 11, 1899 (-15 degrees)
Streak of days with a high 32 degrees or less...
Two... Jan 22-24, 2011
Three... Jan 22-24, 2011
Four... Feb 5-8, 2007
Five +... Jan 23-28, 2004 (6 days)
Streak of days with a high 29 degrees or less...
Two... Jan 29-30, 2010
Three... Jan 15-17, 2009
Four... Feb 5-8, 2007
Five +... Dec 21-25, 1989
