December 2020 Summary – Warmer and Wetter than Average

Blue Hill Observatory December 2020 Summary:

December was warmer, wetter, cloudier and snowier than average. The 24-hour adjusted mean temperature for the month of 34.0 deg F was 4.2 degrees warmer than the 120-year average for December, and it was 2.4 degrees warmer than the 1981-2010 30-year average. The average maximum temperature of 41.1 deg F was 2.0 degrees warmer than the 30-year mean, and the average minimum temperature of 27.2 deg F was 3.6 degrees warmer than the 30-year mean. The highest temperature observed all month was 62F on the 1st, and the lowest temperature was 13F on the 16th and 19th. Overall, the temperature was variable with frequent swings between warm days and cold days. The high temperature on December 25th was 61F, and the mean temperature on that day of 49F tied for the 6th warmest Christmas Day on record. December precipitation was 7.32 inches, which was about three inches more than the long-term 120-year average and about two and a half inches more than the 30-year mean. Two days during the month, the 5th and 25th, each had more than two inches of precipitation, and Christmas Day was also the wettest on record with 2.15 inches of rain, which surpassed the previous daily record of 1.37 inches in 2002. The Christmas Day rainfall was also the greatest precipitation within 24 hours during December. Snowfall for the month was 19.7 inches, which was eight inches more than the long-term mean for December. Most of that snow, 15.1 inches, fell in a single snow storm on the 17th, which was the largest snowfall of the year, and that amount was a new record for the date, surpassing 7.5 inches in 1988. The mean wind speed for the month was 13.3 mph, and the prevailing wind direction was from the west-northwest. The monthly peak wind gust was 68 mph from the south-southeast during the rain storm on the 25th. December was less sunny than average with 112.6 hours of bright sunshine, or 41 percent of possible, which was five percent less than the long-term average.

BHO Warmest Christmas Day (Dec. 25th) Mean Temperature, deg F (1885-2020):

1) 58 in 2015 [64/52/58]2) 53 in 1964 [59/46/53]3) 51 in 2014 [61/41/51]4) 50 in 1965 [57/42/50]   50 in 1979 [56/44/50]6) 49 in 1889 [62/36/49]   49 in 1893 [55/43/49]   49 in 2020 [61/37/49]
9) 47 in 1888 [57/37/47]   47 in 1982 [55/38/47]

Mike Iacono
Chief Scientist
Blue Hill Observatory