October 2018 Summary – Colder and Wetter Than Average

Blue Hill Observatory

October 2018 Summary:

October got off to a warm start then turned colder and brought above normal precipitation. The 24-hour adjusted mean temperature for the month of 50.2 deg F was 1.2 degrees colder than the 120-year average for October and 0.9 degrees colder than the 1981-2010 30-year average. The average maximum temperatures was 58.0 deg F, which was more than two degrees colder than normal, and the average minimum temperature of 42.7 deg F was slightly below normal. The highest temperature for the month was 82F on the 10th, and the minimum on the 10th of 65F surpassed the previous record high minimum temperature for the date of 62F set in 1949. The warm start to the month ended on the 11th; there were only three warmer than normal days during the last 20 days of the month. The lowest temperature was 27F on the 22nd and 26th. The first freeze of the season, 31F, occurred on the 19th, which was one day earlier than the average date of the first temperature of 32F or lower. A total of 5.85 inches of precipitation was measured, which was nearly two inches wetter than the long-term 120-year average and a little over an inch more than the 30-year mean. The greatest amount in 24 hours was 2.08 inches on the 27th. The total precipitation for September and October combined of 15.10 inches was the seventh highest on record. There were three thunderstorm days during October (two more than average for the month), which brought the annual total up to 24. The mean wind speed was 12.0 mph, and the prevailing direction was from the west. A peak gust of 54 mph from the northeast occurred during heavy rains on the 27th. October generally had much below average sunshine, with only 130.0 hours of bright sunshine, or 39 percent of possible, which was 17 percent less than the long-term mean of 56 percent. The combined sunshine during September-October of 256.8 hours (37 percent) was the lowest on record, and it was 19 percent below the long-term mean of 56 percent.

BHO Wettest September-October, inches (1886-2018):

1) 20.54 in 1996
2) 18.53 in 2005
3) 16.72 in 1999
4) 15.98 in 2011
5) 15.48 in 1890
6) 15.43 in 1962
7) 15.10 in 2018
8) 15.01 in 1932

BHO Lowest October Sunshine, hours (1886-2018):

1) 80.5 in 1913 [24%] 2) 120.3 in 1896 [36%] 3) 121.6 in 1919 [37%] 4) 124.9 in 1888 [38%] 5) 127.4 in 1943 [39%] 6) 128.7 in 1890 [39%] 7) 129.4 in 2005 [39%] 8) 129.8 in 1900 [39%] 9) 130.0 in 2018 [39%]
10) 135.9 in 2009 [41%]

BHO Lowest September-October Sunshine, hours (1886-2018):

1) 256.8 in 2018 [37%]
2) 262.5 in 1888 [38%] 3) 272.6 in 1913 [40%] 4) 275.4 in 1889 [40%] 5) 283.7 in 1896 [41%]

Mike Iacono
Chief Scientist
Blue Hill Observatory