Waiting for the first official D.C. freeze...
Closing in on longest freeze-free period on record
This has been a pretty pleasant November, though there have been periods of both well above and well below average temperatures. While a good portion of the area has seen a freeze at this point (i.e., Dulles as low as 28 on the 12th, with 12 lows in November at or below freezing), National Airport (DCA) still has not.
Computer guidance available right now seems to indicate there is not a freeze coming to DCA in the immediate future.
How odd is it that we have not seen it yet? Not that odd, actually. According to NOAA NOWData, the 1971-2000 average for first freeze in Washington is November 15. Keep in mind, this 30-year running normal will change once this year is complete, though the shift should not be major.
Keep on reading for more about climate norms for this time of year and also about another record held by 1980 that 2010 wants to challenge...
During the last decade, covering 2000-09, only two years saw a freeze before November 15, with the earliest on the 4th in 2006. The average date of D.C.'s first official freeze during this smaller, but more recent, period is closer to November 24th (or the Wednesday prior to Thanksgiving this year).
The earliest freeze on record at D.C. happened on October 10, 1895. All of the first eight occurrences on record were prior to 1909. The earliest freeze at DCA is October 20th, occurring in 1972 (31) and again in 1992 (32). The latest freeze on record at D.C. happened not too long ago, Dec. 22, 2001 (29). Of the nine times there has been no freeze at D.C. until December, eight are since 1975 and three happened during 2000-09.
Through (and including) today, there have been 265 freeze-free days at DCA since the last one on Feb. 27. In addition to being the earliest final freeze of a cold season, the Feb. 27 finish for winter 2009-10 freezes is the only time in recorded history that the last freeze has happened in February.
When thought of in context of the massive snowfall seen earlier that month, and an average temperature departure of -3.9 degrees in Feb., the turnaround was really something.
In the image above, the average time between freezes following the end of one cold season and the beginning of the next has been steadily growing in Washington over the course of the years on record. In a linear progression, one may have expected roughly 200 days to pass between the last and first freeze in the late 1800s. These days, it is past 230. Recent years in particular stand out as exceptions in the grand scheme, but perhaps it is more common on the smaller scale.
The 265 freeze-free days in D.C. this year so far puts 2010 in a position to soon climb out of 4th place all time in the category. The two spots right ahead of us are the 266 days in 1978 and 268 days in 2001. Now virtually guaranteed at least second all time, the only number left on the horizon is that of 1980. 275 freeze-free days were observed then.
DCA will need to remain freeze-less through the 29th to tie 1980. As Wes Junker noted earlier this week, the pattern may become colder around then, so it could be a race to the finish.
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