November 2018 Summary – Wettest on Record

Blue Hill Observatory

November 2018 Summary:

November got off to a warm start then turned generally colder and brought record precipitation. The 24-hour adjusted mean temperature for the month of 38.6 deg F was 2.0 degrees colder than the 120-year average for November and 3.5 degrees colder than the 1981-2010 30-year average. The average maximum temperature was 45.2 deg F, which was nearly five degrees colder than normal and the coldest since 44.9 deg F in 1996. The average minimum temperature of 32.4 deg F was more than two degrees below normal. The highest temperature for the month was 65F on the 1st and 2nd. The lowest temperature was 9F on the 22nd and 23rd. The minimum of 9F on the 22nd not only broke the previous daily record of 12F set in 1987, it was the second earliest single-digit temperature ever measured at the Observatory. The maximum of 20F on the 22nd surpassed the previous low maximum temperature for the date of 26F set in 1972 and 2008, and it was the second coldest daily maximum temperature ever observed in November. The 22nd was the coldest Thanksgiving Day ever recorded at the Observatory. The low temperature of 9F on the 23rd tied the record for the date previously set in 1888. Rainfall was copious during November with frequent storms, and a total of 10.31 inches of precipitation was measured, which was nearly six inches wetter than the long-term 120-year average and about five and a half inches more than the 30-year mean. November was the wettest on record and the first to record more than ten inches of precipitation. The greatest amount in 24 hours was 1.78 inches on the 9th-10th. There were fourteen days with measurable precipitation, which is three more than average. Of the seven rain or snow events during the month, six of them brought over an inch of liquid precipitation. November snowfall totaled 7.6 inches, which was 5.0 inches more than the long-term mean. Most of this amount fell during the first snowfall of the season, which brought 7.5 inches on the 15th-16th and was the greatest in 24 hours. The calendar day snowfall of 6.5 inches on the 15th was a new record for the date, surpassing 4.0 inches set in 1967. There were no thunderstorm days during the month. The mean wind speed was 13.4 mph, and the prevailing direction was from the west-northwest. A peak gust of 59 mph from the west followed heavy rain on the 3rd. November had much below average sunshine, with only 102.4 hours of bright sunshine, or 36 percent of possible, which was 11 percent less than the long-term mean of 47 percent. There were twelve days during the month with little or no bright sunshine.

BHO Coldest Thanksgiving Day (Max/Min/Mean Temperature), deg F (1885-2018):

1) 20/9/15 on November 22, 2018
2) 21/10/16 on November 28, 1901
3) 22/14/18 on November 29, 1894
4) 25/11/18 on November 26, 1903
5) 27/13/20 on November 28, 2002
6) 26/16/21 on November 27, 1890
   29/13/21 on November 23, 1972
   27/14/21 on November 28, 1996

BHO Coldest November Daily Maximum Temperature, deg F (1885-2018):

1) 19 on November 30, 1929
2) 20 on November 22, 2018
3) 21 on November 23, 1888
   21 on November 28, 1901
5) 22 on November 29, 1894
   22 on November 27, 1903

BHO Greatest November Precipitation, inches (1886-2018):

1) 10.31 in 2018
2) 9.78 in 1983
3) 9.29 in 1945
4) 9.17 in 1972
5) 8.95 in 1895
6) 8.93 in 1988
7) 8.79 in 1963

Fall (Sep-Nov) 2018 Summary:

Fall 2018 became increasingly cooler than average during the season with a record amount of rainfall. The 24-hour adjusted mean temperature for September-November of 51.2 deg F was just 0.2 degrees warmer than the 120-year average for Fall and 0.7 degree cooler than the 1981-2010 30-year average. Although September was warmer than average, October was near average, and November was colder than average highlighted by the earliest daily maximum temperature of 20 deg F or colder ever recorded at the Observatory on November 22nd. Fall 2018 was the wettest on record with a precipitation total of 25.41 inches, which was about 13 inches more than the long-term mean and about 12 inches more than the 30-year average. With all of the precipitation, Fall was also the cloudiest on record with only 37 percent of the possible bright sunshine, which was 17 percent less than the long-term Fall mean of 54 percent.

BHO Greatest Fall Precipitation, inches (1886-2018):

1) 25.41 in 2018
2) 23.18 in 2005
3) 23.13 in 1996
4) 22.47 in 1888
5) 20.65 in 2011
6) 20.64 in 1932
7) 20.08 in 1962

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

1) 359.2 in 2018 [37%]
2) 388.6 in 1896 [40%] 3) 390.5 in 1888 [40%] 4) 391.1 in 1889 [40%] 5) 405.9 in 1919 [42%]

Mike Iacono
Chief Scientist
Blue Hill Observatory