July 2017 Summary – Drier than Average

Blue Hill Observatory

July 2017 Summary:

July temperature was close to normal with less rainfall than average. The 24-hour mean temperature for the month of 70.2 deg F was 0.5 degrees warmer than the 120-year average for July and about a half degree cooler than the 1981-2010 30-year average. The month was the coolest July since 2009, when the 24-hour mean temperature was 67.6F.  The high temperature of 90F occurred on the 19th, 20th and 21st, which was the only heat wave of the month and the first three-day heat wave of the year. The coldest temperature during July was 54F on the 24th and 25th. The 24th also had the lowest maximum temperature for any day during July of 62F, which tied the record for the date previously set in 1904 and 1964. A total of 3.39 inches of precipitation was measured during July, which was a quarter inch less than the long-term 120-year average and about a half inch less than the 30-year mean. The greatest amount in 24 hours was 1.76 inches (about half the monthly total) during a rain storm on the 24th-25th that brought periods of heavy rain and winds off the ocean from the east-northeast to east. There were two thunderstorm days during July on the 8th and 12th, which brings the annual total up to 12. Through July, there has been at least one thunderstorm day observed in each month so far this year, which has only happened once before (in 1996) during the entire Blue Hill climate record. The mean wind speed for July was 10.0 mph, which was the second lowest on record for the month, and the prevailing direction was from the west. The peak gust was 38 mph from the northeast during the rainfall on the 24th. July bright sunshine was close to average with 259.4 hours or 58 percent of possible, which was equal to the long-term mean.

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

1) 9.8 in 2012
2) 10.0 in 2017
3) 10.1 in 1906
10.1 in 2013
5) 10.2 in 2015
6) 10.3 in 1922

Mike Iacono
Chief Scientist
Blue Hill Observatory