Tuesday, December 2, 2008

DC: Definitely Chilly
Coolest November Since 1997

November's average temperature of 46.6° at Washington's National Airport was 2.1° below the 1971-2000 "normal". This made it the coolest November since the 46.2° in 1997, just barely beating out the 46.7° in 2000. The month was tied with 1937 as the 59th coolest November in 138 years of official records. Although the daily high of 74° on both the 1st and 15th was well above the long-term average, no daily high or low records were seriously threatened. The monthly low of 26° on the 22nd was significantly above the record low of 12° for the date.

Does a relatively cold November predict a cold winter? The lower chart to the right shows the relationship between the November average temperature and the following December-January-February average since 1871. The upward sloping trend line indicates that cold Novembers tend to be associated with relatively colder winters, but the relationship is not very strong. The equation of the trend line indicates that for every 1° change in the November average, the winter average moves in the same direction by about 0.4°. On the other hand, there is a lot of scatter in the data. The "R-squared" says that only 19% of the variability of the winter average temperature is accounted for by the November average.

For more details on regression analysis and a discussion of the relationships between temperature and precipitation, see these blasts from the past:
Images: CapitalClimate charts from NWS data, photos © Kevin Ambrose

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