Washington D.C.’s first official freeze of the 2011-2012 winter, third latest on record

December 12, 2011

Number of first freezes of a winter season, by date, including all years since 1872 at D.C.’s official observating station, Reagan National Airport, (DCA). The average first freeze date for all DCA winters of 11/13 and the current 30-year average of 11/18 are shown in addition to this year’s first one that occurred late on 12/10.

While this year’s first freezes along Potomac river banks (at DCA) took their time, that’s not the case elsewhere. Through today, Dulles has now seen 25 lows of freezing or below and Baltimore-Washington Airport has witnessed 18. That compares to DCA’s 3 season-to-date — the 10th snuck one in at 11:59 p.m. (so one night counted for two days).

In historical context, a December first freeze is somewhat unusual, even by less forgiving (or, increasingly warm) 1981-2010 standards. As noted in “When should the Washington, D.C. area expect to see its first freeze of the cold season?”, only 20% of these most recent seasons experienced their first freeze in December. However, considering there was only one (post November first freezes) prior to 1975 — far back in 1948 — perhaps we should get used to it being more common.

Freeze free days


Number of days between the final freeze and the first freeze of the next season. These tallies do not include either day that has a freezing temperature but the days next to them which do not. A linear progression is shown as a general guide rather than an estimate of the pattern.

The temperature of 32 degrees to close out December 10 (on its way to 29 the morning of the 11th) ended Washington’s (yes, parts of the city have already seen freezes) streak of 256 freeze free days. The last one occurred on March 28, 2011 (just a day off the average spring last freeze date of March 27). The current 30-year average for freeze free days is 236, and the difference between December 10 and the average first freeze by November 18 makes up most of the discrepancy from normal.

Last year, thanks to the earliest final (spring) freeze on record, we nearly reached the record length of time without a freeze at D.C. with 274 days (compared to the leader, 275, in 1980). This year Washington entered the top 10 yet again, finishing tied at 7th with 2009. That seems like quite an unusual accomplishment, except when factoring in a full half of the top 10 freeze free periods have occurred since 2001.

When comparing to the other area climate locations, at Dulles and Baltimore-Washington airports, there are stark differences. This should be expected, at least partly due to DCA’s location on the river with no elevation, and its proximity to the urban concrete jungle.

But, with more than 5 weeks in between the earliest at DCA and at the other locations — October 30 for both — one has to wonder how useful a metric the "official" first D.C. freeze is for the area.

Maybe you can make fun of your friends that see a later freeze than National. Caution: that might instantly label you a weather nerd.

# OF DAYS WITH A FREEZE THRU 12/12

DCA (3): Dec (3); Nov (0); Oct (0) - Earliest: Dec 10 - Lowest: 29 on 12/11 and 12/12

Dulles (25): Dec (9); Nov (14); Oct (2) - Earliest: Oct 30 - Lowest: 19 on 12/12

BWI (18): Dec (9); Nov (7); Oct (2) - Earliest: Oct 30 - Lowest: 22 on 12/12

Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.
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