December 2015 Summary – Warmest on Record

Blue Hill Observatory
December 2015 Summary:

The month was notable for consistently warmer than average temperatures that established a new record for the warmest December by a wide margin. The 24-hour mean temperature for the month of 42.9 deg F was 13.1 degrees warmer than the 120-year average for December, more than 11 degrees warmer than the 1981-2010 30-year average, and 4.8 degrees higher than the previous record for the month. Both the average maximum temperature of 50.5 deg F and the average minimum temperature of 36.9 deg F established new records for December. The monthly mean departure of +13.1 degrees relative to the long-term mean was the largest positive departure for any month on record. The highest temperature for the month of 67F on the 24th tied for the fifth warmest temperature ever recorded in December, and it was also a new daily temperature record for the date, surpassing 61 deg F in 2014. Christmas Day had a maximum temperature of 64 deg F, which was the warmest ever observed and surpassed the previous record for the 25th of 62 deg F in 1889. The coldest temperature of 23F on the 29th and 30th was the highest minimum temperature ever seen in December.  Only one day all month, the 1st, was colder than average, and there were seven days with positive temperature departures of +20 degrees or more, which was a new record for the month. The mean vapor pressure, which is a measure of moisture in the air, averaged 7.8 mb, and this was substantially higher than the previous record for the month of 6.2 mb in 1996. December was slightly drier than average with a precipitation total of 4.27 inches, which was about a half inch less than average. The greatest amount in 24 hours was 1.04 inches on the 28th-29th. The consistent warmth significantly delayed the first measurable snowfall of the season, which finally arrived on the 29th. This tied for the third latest first snowfall since 1885. The monthly snowfall of 1.3 inches, which was about 12 inches less than average, all occurred on the 28th-29th.  The mean wind speed was 11.8 mph, which was the lowest on record for December, with a prevailing direction from the west. A peak gust of 48 mph was observed from the west on the 15th. December was much cloudier than average with only 34 percent of the possible bright sunshine, which was twelve percent less than the long-term mean.

BHO Warmest December 24-Hour Mean Temperature, deg F (1885-2015):

1) 42.9 in 2015
2) 38.1 in 2006
3) 37.5 in 2011
4) 37.3 in 2001
5) 37.2 in 1891
6) 36.9 in 1998
7) 36.7 in 1990

BHO Warmest December NWS Mean Temperature, deg F (1885-2015):

1) 43.7 in 2015
2) 38.4 in 2006
3) 37.8 in 1891
4) 37.5 in 2011
5) 37.3 in 2001
6) 36.9 in 1953
7) 36.8 in 1957
   36.8 in 1990
   36.8 in 1998

BHO Warmest December Average Maximum Temperature, deg F (1885-2015):

1) 50.5 in 2015
2) 45.9 in 1891
3) 45.5 in 2006
4) 45.4 in 2011
5) 45.3 in 1990
6) 45.1 in 1953
7) 44.2 in 1957
   44.2 in 1998

BHO Warmest December Average Minimum Temperature, deg F (1885-2015):

1) 36.9 in 2015
2) 31.2 in 2006
3) 30.8 in 2001
4) 30.5 in 1996
5) 30.1 in 2012
6) 29.6 in 2011
7) 29.5 in 1891

BHO Warmest December Maximum Temperature, deg F (1885-2015):

1) 74 in 1998
2) 72 in 1984
3) 70 in 2001
4) 68 in 1966
5) 67 in 1979
   67 in 2009
   67 in 2015
8) 65 in 1911
   65 in 1982
   65 in 2006

BHO Warmest December Minimum Temperature, deg F (1885-2015):

1) 23 in 2015
2) 18 in 2001
3) 17 in 2006
   17 in 2012
5) 15 in 1907
   15 in 1913
7) 14 in 1923
   14 in 2011
   14 in 2014

BHO Largest December Daily Temperature Departure from 30-Year Normal, deg F (1885-2015):

1) +35 on 29 Dec 1984  (72/51/62)
2) +30 on 25 Dec 2015  (64/52/58)
3) +29 on 23 Dec 1990  (62/53/58)
   +29 on 24 Dec 2015 (67/48/58)
5) +27 on 31 Dec 1965  (62/45/54)
   +27 on 22 Dec 1990  (58/53/56)
7) +26 on 27 Dec 1949  (57/51/54)
   +26 on 9 Dec 1966  (68/52/60)
   +26 on 6 Dec 2001  (70/52/61)

BHO Largest Monthly 24-Hour Mean Temperature Departure from 120-Year Mean, deg F (1885-2015):

1) +13.1 in December 2015
2) +9.9 in January 1913
3) +9.3 in January 1932
4) +9.1 in March 1946
5) +9.0 in March 2012
6) +8.9 in January 1937
7) +8.5 in February 1984
8) +8.3 in March 1945
   +8.3 in December 2006
10) +8.2 in January 2006

BHO Highest December Vapor Pressure, mb (1885-2015):

1) 7.8 in 2015
2) 6.2 in 1996
3) 6.0 in 1973
   6.0 in 1982
   6.0 in 2012
6) 5.8 in 1990
   5.8 in 2011
   5.8 in 2014

BHO Latest First Measurable Snowfall, (1885-2015):
1) January  13, 2000  (7.0 inches)
2) January   1, 1954  (0.8 inches)
3) December 29, 1941  (0.4 inches)
   
December 29, 2015  (1.3 inches)
5) December 22, 1998  (0.6 inches)
6) December 16, 1973  (0.4 inches)
7) December 15, 1891  (0.3 inches)

BHO Lowest December Mean Wind Speed, mph (1885-2015):

1) 11.8 in 2015
2) 12.2 in 2014
3) 12.3 in 2013
4) 12.9 in 2001
5) 13.0 in 2012
6) 13.1 in 2007
7) 13.4 in 2011

BHO Lowest December Sunshine, hours (1885-2015):

1) 72.9 in 1972   [27%] 2) 81.0 in 1982   [29%] 3) 87.2 in 1933   [32%] 4) 88.2 in 1996   [32%] 5) 89.0 in 1922   [32%] 6) 89.5 in 1981   [33%] 7) 91.1 in 1906   [33%] 8) 92.0 in 2012   [34%] 9) 92.9 in 2013   [34%] 10) 93.3 in 2015   [34%]