December 2025 Summary – Colder and Drier Than Average

Blue Hill Observatory December 2025 Summary: 

December 2025 was colder and drier than normal with less snowfall and much more sunshine than average. The approximated 24-hour mean temperature for the month of 28.9 deg F was 1.2 degrees colder than the 1891-2020 130-year average for December, and it was 3.9 degrees colder than the 1991-2020 30-year average. The month was the coldest December since 2017, and it tied as the fourth coldest since 1990. The average maximum temperature of 36.0 deg F was 4.2 degrees colder than the 30-year normal. The average minimum temperature of 20.9 deg F was 4.0 degrees colder than the 30-year normal, and this measure was the coldest since 2000. The chilly weather continued throughout the month, though there were no daily temperature records, and there were only seven days that averaged warmer than normal. The highest temperature for the month was 58F on the 19th, and the lowest temperature was 8F on the 5th and 26th. December mean water vapor pressure, which is an absolute measure of water vapor in the air, was 3.8 mb, which corresponded to a mean dew point of about 22F. This amount was below the long-term mean water vapor pressure for December of 4.5 mb, which equals a mean dew point of about 26F. The total precipitation was 2.73 inches, which was 2.66 inches less than the 30-year normal. There were no significant storms during the month, though there were several strong frontal passages and smaller rain and snow events. The greatest liquid equivalent precipitation in 24 hours was 0.91 inches on the 2nd-3rd, which was mostly rain that ended as a small snowfall on the 3rd. The total snowfall during December was 6.8 inches, which was 5.8 inches less than normal. There were no thunderstorm day during the month. The lowest sea-level pressure was 29.19 inches during the passage of an Arctic front following a period of rainfall on the 29th, and the highest sea-level pressure was 30.41 inches on the 22nd. It was a relatively windy month, and the mean wind speed was 13.7 mph with a prevailing wind direction from the west. The highest wind gust was 79 mph from the south ahead of another strong cold front on the 19th. Wind gusts exceeded 50 mph on eight days. December sunshine was much above average with 150.0 hours of bright sunshine, or 55 percent of possible, which was nine percent more than the long-term average for the month.

Mike Iacono
Chief Scientist
Blue Hill Observatory