2023 Summary – Second Warmest Year on Record

The year 2023 was exceptionally warm and ranked as the second warmest on record. The approximated 24-hour mean temperature of 51.5F was 3.7F warmer than the 130-year (1891-2020) long-term mean and 2.0F above the 30-year (1991-2020) average. Ten months were warmer than the long-term mean; only June and November were cooler. The annual average maximum temperature of 60.6F, which tied as the third warmest on record, was 2.3F warmer than the 30-year normal. The annual average minimum temperature of 43.9F was 2.8F warmer than the 30-year normal, and it was the second warmest on record. Each of the last four years was among the eight warmest years on record, and the ten warmest years since 1885 have all occurred since 1998.

The year started very warm and wet with the second warmest January. Four days had high temperatures above 50F, and the coldest temperature was only 18F during January. Two very cold days in early February, which included a low of -11F on the 3rd and the lowest temperature of the year of -14F on the 4th, both daily records, did not prevent a generally very warm February that also included six days that reached 50F or more. The daily low temperature of 50F on February 16th tied the record for the warmest minimum on any February day. The warmth continued into the spring months including two consecutive days that set daily high temperature records of 88F on April 13th and 14th. June was slightly cooler than average despite a warm start that included a high temperature of 91F on the 2nd. July was warm and very wet with a high temperature of 92F on July 6th, the warmest of the year. August was generally cooler than average with no days above 90F, and there were no heat waves during 2023. September was slightly warmer than average and included a day that reached 92F on the 7th, tying the warmest temperature of the year, that was only the fourth and last 90-degree day all year. Warmth returned in October, which had eight days with high temperatures above 70F and three days of 80F or more, including one of the latest readings of 80F on record on October 28th. November was cooler than average, but the year finished warm with the second warmest December that included two days that reached 61F on the 11th and the 18th. Winter 2022-2023 was the fourth warmest on record. 

Ponkapoag Pond was considered free of ice for the 2022-2023 winter season on March 5th, eleven days earlier than the long-term mean date, and Houghton’s Pond also thawed on March 5th, 15 days earlier than the mean date. The first ripe blueberries were observed on the summit of Great Blue Hill on June 27th, which was six days later than the average date. Late in the year, Ponkapoag Pond and Houghton’s Pond had not yet frozen over through the end of December 2023 due to the warm weather that month.

Post-tropical cyclone and former Hurricane Lee passes east of New England on the morning of 16 September 2023. Image courtesy of the College of DuPage NEXLAB (weather.cod.edu).

The annual rainfall of 58.70 inches was nearly ten inches more than the 130-year average and nearly five inches more than the 30-year normal. A wet January started the year with twenty days having measurable precipitation including twelve days in a row on the 12th-23rd. This period included 10.1 inches of the month’s 12.2 inches of snow, which was several inches below average. February was also dry with less snow than average. March was warm and wet, including a major storm on March 13th-15th that brought 3.73 inches of liquid equivalent precipitation and the largest snowfall of the year of 7.2 inches. After relatively dry weather from April to early June, July was the wettest month of the year with 9.59 inches, and it was the sixth wettest July on record. The two wettest days brought 2.56 inches on July 16th and 1.99 inches on the 21st. Summer 2023 was the seventh wettest on record. September was another wet month with several heavy rainfall events that included 1.92 inches of rain on the 13th and 1.56 inches on the 18th. There were impacts from two tropical cyclones during September including former Hurricane Lee, which brought 0.21 inches of rain and a peak wind gust to 44 mph from the west-northwest as it passed to the east as a post-tropical cyclone on the 16th and former Tropical Storm Ophelia, which brought 1.10 inches of rain and a peak wind gust to 38 mph from the east-northeast as it passed to the south as a post-tropical system on the 23rd-25th. October and November were drier than average. Wet weather returned in December, though there was little snowfall. One strong storm brought 2.62 inches of rain on the 10th-11th, and a more powerful rain and wind storm brought 2.94 inches on the 17th-18th that caused widespread power outages across the area and a record wind gust of 90 mph to Blue Hill. There were 28 thunderstorm days during 2023, which was six more than average, including ten in July and six in September.

Snowfall was below average during every month from January to April. January had 12.2 inches including 3.9 inches on the 15th-16th and 4.1 inches on the 23rd. Most of the 9.4 inches of snow in February fell in several small events during the last eight days. The largest snowfall of the year was 7.2 inches on March 14th-15th at the end of a major storm that started as rain on the 13th. There was only a trace of snow in November and only 0.3 inches in December, and the snowfall for the calendar year of 32.5 inches was less than half of the 30-year normal annual snowfall of 69.7 inches. The annual snowfall was the 12th lowest on record and the lowest since 31.1 inches in 2012. The period of snowless days between March 15th and December 6th, 266 days, was the sixth longest ever observed. 

The mean station pressure during 2023 at the elevation of the mercury barometer at the Observatory was 29.29 inches, which was equal to the long-term annual mean of 29.29 inches. The maximum sea-level pressure during the year was 30.63 inches on December 14th, and the lowest sea-level pressure during 2023 was 28.96 inches four days later during the strong rain and wind storm on December 18th.

A major storm brings heavy rain and very strong winds across eastern New England on December 18, 2023. NOAA GOES-16 visible satellite imagery courtesy of COD NEXLAB Weather (weather.cod.edu).

Water vapor pressure, which is derived from the dew point and is an absolute measure of the amount of moisture in the air in terms of the pressure that water vapor contributes to the total surface pressure, averaged 11.1 mb (0.328 inches) during 2023. This value was highest on record and continued a trend of higher vapor pressures in recent decades, which is consistent with the increasing trend in temperature. Another way to interpret this value is to state that water vapor on average comprised a little over one percent of the total annual mean station pressure during the year.

The annual mean wind speed of 10.8 mph was the lowest on record for any year. This average continued the several decades long trend of decreasing mean wind speeds on Blue Hill. Seven months during the year also set new record low average wind speeds. The peak gust for the year of 90 mph from the south-southeast during the major storm on December 18th was the highest gust on Great Blue Hill since 91 mph was observed on January 27th, 1996. Other notable wind gusts during the year included 69 mph from the south-southwest on December 11th and 61 mph from the west-northwest on July 27th.

Bright sunshine for the year was 53 percent of possible, which was one percent more than the long-term average. The least sunny month was January with only 73.2 hours or 26 percent of the possible bright sunshine, which was a new record low for the month and in terms of hours the second lowest sunshine for any month of the year. The sunniest month during 2023 was May, which had 329.9 hours or 75 percent of the possible sunshine. This amount was a new record for May and the fourth sunniest in terms of hours for any month of the year.

BHO Warmest Annual Approximated 24-Hour Mean Temperature, deg F (1885-2023):

1) 51.7 in 2012
2) 51.5 in 2023
3) 51.3 in 2020
4) 51.2 in 2016
5) 51.1 in 2022
6) 51.0 in 2010
7) 50.9 in 1999
   50.9 in 2021

BHO Warmest Annual Average Maximum Temperature, deg F (1885-2023):

1) 60.9 in 2022
2) 60.8 in 2012
3) 60.6 in 2016
   60.6 in 2023
5) 60.5 in 1949
6) 60.4 in 2020
7) 60.2 in 1999

BHO Warmest Annual Average Minimum Temperature, deg F (1885-2023):

1) 44.0 in 2012
2) 43.9 in 2023
3) 43.4 in 2020
4) 43.2 in 1998
5) 43.1 in 2021
   43.1 in 2006
7) 43.0 in 2010

BHO Longest Periods Between Measurable Snowfall Days (1886-2023):

1) 304 days, 15 March 1999 – 13 January 2000
2) 287 days, 17 March – 29 December, 1941
3) 276 days, 28 March – 29 December, 2015
4) 270 days, 6 March – 1 December, 1902
5) 269 days, 22 March – 16 December, 1973
6) 266 days, 15 March – 6 December, 2023
7) 265 days, 12 March – 2 December, 1983
8) 264 days, 13 March – 2 December, 1966
9) 262 days, 12 March – 29 November, 1948
   262 days, 14 April 1953 – 1 January 1954

BHO Highest Annual Mean Water Vapor Pressure, mb (1932-2023):

1) 11.1 in 2023
2) 11.0 in 2012
   11.0 in 2018
4) 10.9 in 2011
   10.9 in 2021
6) 10.8 in 2020
7) 10.7 in 1973
   10.7 in 2022

BHO Lowest Annual Mean Wind Speed, mph (1885-2023):

1) 10.8 in 2023
2) 11.5 in 2021
3) 11.8 in 2012
4) 12.0 in 2020
   12.0 in 2022
6) 12.1 in 2018
   12.1 in 2019

Mike Iacono
Chief Scientist
Blue Hill Observatory