June 2021 Summary – Warmest on Record

Blue Hill Observatory June 2021 Summary:

June was the warmest on record, and it was much drier and sunnier than average. The 24-hour adjusted mean temperature for the month of 70.0 deg F was 5.7 degrees warmer than the 1891-2020 130-year average for June, and it was more than 4 degrees warmer than the 1981-2010 30-year average. In addition to being the warmest June on record, it was the first June to average as high as 70 deg F. The month also surpassed the previous record for the month, 68.7 deg F in 1999, by 1.3 degrees, which is a very large jump in mean for a new monthly record. The average maximum temperature of 80.9 deg F was 6.2 degrees warmer than the 130-year mean, and the average minimum temperature of 60.4 deg F was 4.8 degrees warmer than the 130-year mean. Both the average maximum and average minimum temperatures for June were also new records for the month. The highest temperature observed all month was 95F on the 29th, which was also a new record high temperature for the date, surpassing 94F set in 1933. The high temperature of 94F on the 30th tied the record for that date, which was previously set in 1964. There were two three-day heat waves during the month, which has never occurred before in June on the entire record at Blue Hill, including high temperatures of 90F or more on the 6th-8th and again on the 28th-30th. The six 90-degree days tied the record for June previously set in 1997. The lowest temperature for the month was 50F on the 1st. The mean water vapor pressure, which is an absolute measure of the amount of water vapor in the air, was 18.1 mb, which was also the highest on record for the month since 1932. June total precipitation was 2.72 inches, which was 1.08 inches less than the long-term 130-year average and about an inch and a half less than the 1981-2010 30-year mean. The greatest precipitation in 24 hours was 0.68 inches during a thunderstorm on the 22nd. There were six thunderstorm days during June, which was two more than average, and the annual total for the first half of the year is nine. The mean wind speed for the month was 10.9 mph, and the prevailing wind direction was from the south-southwest. The monthly peak wind gust was 51 mph from the northwest during the rain and thunderstorms on the 30th. June sunshine was above average with 270.5 hours of bright sunshine, which was 62 percent of the possible sunshine and seven percent more than the 130-year mean.

BHO Warmest June 24-Hour Adjusted Mean Temperature, deg F (1885-2021):

1) 70.0 in 2021
2) 68.7 in 1999
3) 68.5 in 2001
4) 68.3 in 1925
   68.3 in 1930
6) 68.2 in 1994
7) 68.0 in 1943

BHO Warmest June Average Maximum Temperature, deg F (1885-2021):

1) 80.9 in 2021
2) 80.4 in 1930
3) 80.3 in 1949
4) 79.5 in 1957
   79.5 in 1976

BHO Warmest June Average Minimum Temperature, deg F (1885-2021):

1) 60.4 in 2021
2) 59.9 in 1925
3) 59.8 in 2001
4) 59.7 in 1999
5) 59.5 in 2008

BHO Highest June Water Vapor Pressure, mb (1932-2021):

1) 18.1 in 2021
2) 18.0 in 1973
3) 17.9 in 2005
4) 17.7 in 1976
5) 17.6 in 2006
6) 17.5 in 2010
7) 17.4 in 1994

Mike Iacono
Chief Scientist
Blue Hill Observatory