September 2020 Summary – Warmer and Drier Than Average

Complete undercast as photographed from the Blue Hill Observatory looking west on the morning of August 23, 2020. Photo by Matthew Douglas.

Blue Hill Observatory September 2020 Summary:

September was warm and generally dry with above average sunshine. The 24-hour adjusted mean temperature for the month of 63.6 deg F was 2.4 degrees warmer than the 120-year average for September, and it was 1.5 degrees warmer than the 1981-2010 30-year average. The average maximum temperature of 73.2 deg F was 1.6 degrees warmer than the 30-year mean, while the average minimum temperature of 54.9 deg F was just 0.3 degrees warmer than the 30-year mean. The highest temperature observed all month was 82F on the 4th and 8th, and the lowest temperature was 39F on the 22nd. The year to date for January through September was the fourth warmest on record. September precipitation totaled 1.61 inches, which was almost two and a half inches less than the long-term 120-year average and the 30-year mean. This deficit significantly added to the ongoing moderate to severe drought over the area. The greatest precipitation in 24 hours was 1.02 inches on the 29th-30th, mostly during the passage of a cold front with strong winds on the 30th. There were no thunderstorm days during September, and the total for the year remains 17. The mean wind speed for the month was 11.1 mph, and the prevailing wind direction was from the south. The monthly peak gust was 71 mph from the south on the 30th. September sunshine was close to average with 202.5 hours of bright sunshine, or 56 percent of possible, which was one percent less than the long-term average.

Mike Iacono
Chief Scientist
Blue Hill Observatory