2017 Was Warmer and Wetter Than Average

The year 2017 ended with a 24-hour corrected mean temperature of 50.3F, which was 2.7F warmer than the 120-year mean and 1.4F above the 30-year normal, and this mean was warm enough for 2017 to tie for the ninth warmest year on record. The annual average maximum temperature of 59.1F was the 15th warmest on record, and the annual average minimum temperature of 42.4F was the eighth warmest on record. The year got off to a very warm start with both January and February seven degrees or more warmer than the long-term mean, and Winter 2016-2017 (December-February) finished as the fourth warmest on record. There was an exceptionally warm three-day period on February 23rd-25th that included a new record high temperature for the month of February of 71F, which occurred on the 24th. This surpassed the previous record for the month of 68F set in 1985. This interval was the warmest consecutive 3-day period of maximum temperatures for any winter month on record. The warm was interrupted in March, which was unusually cold, with the temperature dropping to a low of 4F on March 12th. For only the fourth time since 1885, March was colder than February. March was also colder than the preceding winter (Dec-Feb) mean temperature for the first time since 1959-1960. Warm returned in April, which was the third warmest on record, then retreated again in early May. The average high temperature for the first 15 days of May was the sixth coldest on record and the coldest since 1962. A brief warm period in the middle of May brought several daily records including 96F on the 18th, which was also a new high temperature record for the month of May. After a slightly warm summer, much warmer weather returned in September and especially October, which was the warmest on record. November started warm then turned sharply colder at mid-month when a low temperature of 18F on November 11th represented only the fourth time on the entire Blue Hill period of record that a temperature in the teens was observed this early in the season. December temperature was close to average until a sharp cold spell began after a snowfall on Christmas Day that included the coldest temperature of the year, -3F, on December 29th.

Due to the warmth in late February, both Houghton’s Pond and Ponkapoag Pond were considered free of ice on February 25th, about three weeks earlier than the average date. The first ripe blueberries were observed on the summit of Great Blue Hill on June 19th, which was only slightly earlier than the average date. Late in the year, warm periods in early December delayed the freeze of both Houghton’s and Ponkapoag until December 15th, 2017, which was a few days later than the long-term mean date.

During the solar eclipse on the afternoon of August 21st, 2017, when 63 percent of the Sun was obscured by the Moon at Blue Hill at the peak of the eclipse, both a reduction in temperature of several degrees and a reduction in solar intensity were recorded at the Observatory.

Annual precipitation totaled 52.92 inches, which was more than four inches wetter than the 120-year average and about a half inch less than the 1981-2010 30-year average. Precipitation remained near average much of the year. Seven months during 2017 exceeded the long-term average precipitation with the wettest period occurring from April through June. August was the driest month with only 1.60 inches, and April was the wettest month with 6.69 inches. There were 18 days with thunderstorms during the year, which was four fewer than average. Thunder was observed during heavy snow on February 9th. Thunderstorms on August 2nd brought over an inch of rain, most of that month’s total, in just a few hours. The heaviest rainfall event of the year occurred on October 29th-30th, when the year’s greatest rainfall in 24 hours, 3.12 inches, was measured during the passage of a very strong storm that also brought the highest wind gust of the year of 73 mph and a minimum sea-level pressure of 29.03 inches on the 30th, which was one of the lowest pressures ever recorded in October.

Snowfall for the calendar year was above average with a total of 67.9 inches, or seven inches more than the long-term annual average of 61 inches. Almost half of this snowfall, 31.5 inches, fell in February. The largest single snowfall during the year of 16.9 inches occurred on February 9th, and this storm was followed by another 13.5 inches during several events over the following week. The snow depth reached its high point of the year of 15 inches during this time. The final snowfall total for the 2016-2017 season (Oct-Apr) was 66.4 inches, which was a few inches more than the long-term average seasonal snowfall.

The mean station pressure at the elevation of Great Blue Hill during 2017 was 29.30 inches, which was 0.01 inches higher than the long-term annual mean of 29.29 inches. The highest sea-level pressure during the year was 30.69 inches on January 14th. The lowest sea-level pressure during 2017 of 28.87 inches occurred on March 14th during a late winter snowstorm that brought 7.3 inches of snow, 2.15 inches of melted precipitation and a wind gust of 60 mph from the NE.

The annual mean wind speed of 12.2 mph tied for the second lowest on record with 2013 and 2015, each higher than only the 11.8 mph mean observed in 2012. This continues the several decade long trend of decreasing mean wind speeds on Blue Hill, though the trend has moderated in the last few years. The peak wind gust during 2017 was 73 mph from the SE during the passage of a strong storm on October 30th.

Bright sunshine for the year was 52 percent of possible, which was exactly equal to the long-term average.

BHO Warmest Annual 24-hour Corrected Mean Temperature, deg F (1885-2017):

1) 51.7 in 2012
2) 51.2 in 2016
3) 51.0 in 2010
4) 50.9 in 1999
5) 50.8 in 1998
6) 50.6 in 2006
7) 50.5 in 1953
8) 50.4 in 2011
9) 50.3 in 1990
   50.3 in 1991
   50.3 in 2017

BHO Warmest Annual Mean Minimum Temperature, deg F (1885-2017):

1) 44.0 in 2012
2) 43.2 in 1998
3) 43.1 in 2006
4) 43.0 in 2010
5) 42.8 in 2016
6) 42.7 in 1999
   42.7 in 2011
8) 42.4 in 2017
9) 42.3 in 1949
   42.3 in 1953
   42.3 in 2001

BHO Lowest Annual Mean Wind Speed, mph (1885-2017):

1) 11.8 in 2012
2) 12.2 in 2013
   12.2 in 2015
   12.2 in 2017
5) 12.3 in 2014
   12.3 in 2016
7) 12.5 in 2011
8) 12.6 in 2008
   12.6 in 2009

Mike Iacono
Chief Scientist
Blue Hill Observatory