December 2019 Summary – Warmer and Wetter Than Average

Blue Hill Observatory December 2019 Summary:

After a very cold start, December was generally mild with much more precipitation and more snowfall than average. The 24-hour adjusted mean temperature for the month of 32.3 deg F was 2.5 degrees warmer than the 120-year average for December and 0.7 degrees warmer than the 1981-2010 30-year average. The average maximum temperature of 39.1 deg F was exactly average, while the average minimum temperature of 25.0 deg F was 1.4 degrees warmer than average. The warmest temperature for the month was 58F on the 10th and 14th, and the lowest temperature was 9F on the 19th. Precipitation totaled 7.81 inches, which was about three inches more than the long-term 120-year average and about three and a half inches more than the 30-year mean. The greatest precipitation in 24 hours was 1.64 inches on the 1st-2nd during a 48-hour rain and snow storm on the 1st-3rd. Snowfall totaled 19.9 inches, which was about seven inches more than the 30-year mean. The month started very snowy with 13.1 inches over the first three days, and the daily total of 5.7 inches on the 1st was a new record for the date, surpassing the previous record of 2.0 inches in 1902. There were no thunderstorm days during December, and the final yearly total was 17, or five fewer than average. The local ponds completely froze over a few days early this season with Ponkapoag Pond freezing on December 3rd and Houghton’s Pond freezing over on the 8th. The mean wind speed for December was 13.6 mph, and the prevailing wind direction for the month was from the west. The monthly peak gust was 53 mph from the south on the 9th and again from the west on the 15th. December was much cloudier than average with 102.8 hours of bright sunshine, or 37 percent of possible, which was nine percent less than the long-term average.

Mike Iacono
Chief Scientist
Blue Hill Observatory