May 2018 Summary – Third Warmest on Record

Blue Hill Observatory

May 2018 Summary:

May got off to a very warm start and remained generally warm with a few cool days, and it brought about half the normal precipitation. The 24-hour adjusted mean temperature for the month of 61.0 deg F was 5.7 degrees warmer than the 120-year average for May and about five degrees warmer than the 1981-2010 30-year average. The month tied for the third warmest May on record. The highest temperature for the month was 90F on the 3rd, and the coldest temperature was 39F on the 1st. The average maximum temperature during May of 72.2F was the fifth warmest on record, and the average minimum temperature of 51.3F was the second warmest on record for May. A total of 2.01 inches of precipitation was measured, which was 1.69 inches less than the long-term 120-year average and about two inches less than the 30-year mean. The greatest precipitation in 24 hours was 0.74 inches, which occurred during a thunderstorm on the 15th. There were three thunderstorm days during May on the 15th, 20th, and 23rd, and small hail was observed during the thunderstorms on the 15th and 23rd. The final snowfall for the 2017-2018 season was 92.8 inches, which was about 30 inches more than the long-term average and the 30-year normal. The mean wind speed for May was 10.8 mph, which was the second lowest on record, and the prevailing direction was from the south-southwest. A peak gust of 56 mph from the west occurred on the 5th. May sunshine was close to average with a total of 222.1 hours of bright sunshine, or 51 percent of possible, which was one percent less than the long-term mean.

BHO Warmest May Mean Temperature (24-hour adjusted mean), deg F (1885-2018):

1) 61.5 in 2015
2) 61.4 in 1991
3) 61.0 in 1944
   61.0 in 2018
5) 60.9 in 2010
6) 59.4 in 1911
   59.4 in 1959
8) 59.3 in 1964
   59.3 in 2012

BHO Warmest May Average Maximum Temperature, deg F (1885-2018):

1) 74.6 in 2015
2) 74.4 in 1944
3) 73.9 in 1991
4) 72.3 in 2010
5) 72.2 in 2018
6) 71.9 in 1955
7) 71.8 in 1911
   71.8 in 1964

BHO Warmest May Average Minimum Temperature, deg F (1885-2018):

1) 52.5 in 2012
2) 51.3 in 2018
3) 51.2 in 1944
4) 50.5 in 1979
5) 50.4 in 2010
6) 50.3 in 1991
7) 50.1 in 1998

BHO Lowest May Mean Wind Speed, mph (1885-2018):

1) 10.0 in 2012
2) 10.8 in 2018
3) 11.1 in 2017
4) 11.2 in 1982
   11.2 in 2003
6) 11.3 in 2013
   11.3 in 2016

Spring (Mar-May) 2018 Summary:

Spring 2018 started relatively cool and wet and ended warm and dry. The 24-hour adjusted mean temperature for March-May of 46.0 deg F was 1.2 degrees warmer than the 120-year average for Spring and just one tenth of a degree cooler than the 1981-2010 30-year average. The Spring precipitation total was 17.19 inches, which was just under five inches more than the long-term mean and about three inches more than the 30-year average. The greatest rainfall in 24 hours was 3.47 inches during a strong Nor’easter on March 2nd, which also brought the strongest wind gust during Spring of 73 mph from the north-northeast. Spring snowfall totaled 48.1 inches, most of which fell during several March snowstorms, and this amount was the fourth highest Spring snowfall on record. The three thunderstorm days during Spring were all observed during May. Spring was cloudier than average with 45 percent of the possible bright sunshine, which was five percent less than the long-term mean.

Mike Iacono
Chief Scientist
Blue Hill Observatory