December 2017 Summary – Colder and Drier Than Average

Blue Hill Observatory

December 2017 Summary:

After a warm start, December ended on a very cold note, and the month was much drier than normal. The 24-hour mean temperature for the month of 27.2 deg F was 2.6 degrees colder than the 120-year average for December and about four degrees colder than the 1981-2010 30-year average. This month was the coldest December since 26.5 deg F was recorded in 2000. The high temperature was 58F on the 5th, and the coldest temperature was -3F on the 29th, which was also the coldest reading of the year. The warm start to the month turned colder after mid-December, and a severe cold spell began on the 27th. The last five days of the month each averaged 15 degrees or more colder than normal. A total of 3.08 inches of precipitation was measured during the month, which was almost two inches less than the long-term 120-year average and about an inch and a half less than the 30-year mean. Snowfall totaled 9.3 inches, which was two inches less than the long-term mean, and about four inches less than the 30-year average. Most of this snow fell in a 5.6 inch snowfall on the 9th-10th, which was the first measurable snow of the season occurring about three weeks later than average. Another 3.2 inches of snow arrived on the 25th, which was the fifth greatest snowfall on record on Christmas Day. The mean wind speed for December was 12.0 mph, which was the second lowest for the month, and the prevailing direction was from the west. A peak gust of 62 mph from the south occurred on the 5th with warm temperatures that day in the upper 50s. December was less sunny than average with a total of 118.6 hours of bright sunshine, or 43 percent of possible, which was three percent less than the long-term average for the month.

BHO December Lowest Mean Wind Speed (1885-2017):

1) 11.8 in 2015
2) 12.0 in 2017
3) 12.2 in 2014
4) 12.3 in 2013
5) 12.9 in 2001

Mike Iacono
Chief Scientist
Blue Hill Observatory