October 2020 Summary – Wetter and Snowier Than Average

Blue Hill Observatory October 2020 Summary:

October was warm and wet with one very snowy day. The 24-hour adjusted mean temperature for the month of 52.7 deg F was 1.6 degrees warmer than the 120-year average for October, and it was 1.3 degrees warmer than the 1981-2010 30-year average. The average maximum temperature of 61.2 deg F was 0.9 degrees warmer than the 30-year mean, while the average minimum temperature of 45.5 deg F was 2.6 degrees warmer than the 30-year mean. The highest temperature observed all month was 75F on the 1st and 10th, and the lowest temperature was 24F on the 31st following the snowfall on the previous day. The year to date for January through October was the fourth warmest on record. October precipitation totaled 6.75 inches, which was almost three inches more than the long-term 120-year average and about two inches more than the 30-year mean. Nearly six inches of the monthly total fell within three 24-hour periods, including the greatest precipitation in 24 hours, which was 2.24 inches on the 16th-17th. There was one thunderstorm day during the month on the 7th, which was accompanied by very strong winds and pea-sized hail. The total thunderstorm days for the year is 18, which is four fewer than average. Snowfall for the month totaled 6.5 inches, which was the third largest on record for October. All of this snow fell on the morning of the 30th as cold air moved into the area toward the end of a complex weather system that included the passing remnants of Hurricane Zeta and a following coastal storm, which brought steady rain on the 29th into the early morning hours of the 30th before the rain changed to heavy, wet snow. A liquid equivalent storm total precipitation (rain plus melted snow) of 2.20 inches was observed during this storm. The snow on the 30th was a new record for the date, surpassing 2.0 inches in 2011, and it was the second largest snowfall ever measured in October. The mean wind speed for the month was 11.3 mph, which was the second lowest on record for October, and the prevailing wind direction was from the south. The monthly peak wind gust was 76 mph from the south during the thunderstorm on the 7th. October sunshine was well below average with 166.8 hours of bright sunshine, or 50 percent of possible, which was six percent less than the long-term average.

BHO Snowiest October, inches (1891-2020):

1) 8.5 in 2011
2) 6.8 in 1979
3) 6.5 in 2020
4) 4.2 in 1934

BHO Largest October Snowfalls, inches (1891-2020):

1) 6.8 on 10 October 1979
2) 6.5 on 30 October 2020
3) 6.0 on 29-30 October 2011
4) 4.2 on 13 October 1934
5) 3.0 on 23 October 1891
3.0 on 24-25 October 1960
3.0 on 26 October 1962
3.0 on 18 October 2009
9) 2.5 on 27 October 2011

BHO Lowest October Mean Wind Speed, mph (1885-2020):

1) 11.2 in 2013
2) 11.3 in 2020
3) 11.8 in 1997
   11.8 in 2016
5) 11.9 in 1994
   11.9 in 2004

Mike Iacono
Chief Scientist
Blue Hill Observatory