Blue Hill Observatory May 2026 Summary:
May 2026 was generally warm with below average precipitation, snowfall and sunshine. The approximated 24-hour mean temperature for the month of 58.4 deg F was 2.9 degrees warmer than the 1891-2020 130-year average for May, and it was 1.7 degrees warmer than the 1991-2020 30-year average. The average maximum temperature of 68.9 deg F was 2.1 degrees warmer than the 30-year normal, and the average minimum temperature of 49.1 deg F was 0.9 degrees warmer than the 30-year normal. Despite several cool and rainy periods during May, the third week of the month was very warm. The highest temperature was 95F on the 19th, which surpassed the previous record for the date of 91F in 1962, and it was both the second warmest temperature ever observed in May and the second highest so early in the season. The lowest temperature was 39F on the 31st. May mean water vapor pressure, which is an absolute measure of water vapor in the air, was 11.5 mb, which corresponded to a mean dew point of about 48F. This amount was above the long-term mean water vapor pressure for May of 10.5 mb, which equals a mean dew point of about 46F. May rainfall was near average with a total precipitation of 3.13 inches, which was 0.69 inches less than the 30-year normal., but precipitation was frequent during the month. Fifteen days had measurable precipitation, while another six days had at least a trace, and there were no periods without rainfall longer than two days. The greatest amount in 24 hours was 0.89 inches during a cold and breezy rainstorm on the 29th-30th. There was no snow during May, and the final snowfall for the 2025-2026 season was 81.6 inches, which was 11.9 inches more than the 30-year normal. There was one thunderstorm day during May on the 19th, which was two fewer than average. The highest sea-level pressure was 30.53 inches on the 23rd, and the lowest sea-level pressure was 29.62 inches during the storm on the 30th. The mean wind speed was low at 11.2 mph, and the prevailing wind direction was from the south-southwest. The highest wind gust was 53 mph from the north-northeast on the 30th. May sunshine was below average with 216.0 hours of bright sunshine, or 49 percent of possible, which was three percent less than the long-term average for the month. A very unusual occurrence, the loud sonic-boom from a meteor exploding through the atmosphere about 40 miles to the east of the Observatory, was heard in the vicinity shortly after 1 PM EST on the afternoon of the 30th.
BHO Warmest May Temperatures, deg F (1885-2026):
1) 96 on 18 May 2017
2) 95 on 19 May 2026
3) 94 on 26 May 2010
4) 93 on 10 May 1896
93 on 15 May 1900
93 on 22 May 1911
93 on 29 May 1919
93 on 30 May 1929
93 on 7 May 1930
93 on 9 May 2000
93 on 22 May 2022
Mike Iacono
Chief Scientist
Blue Hill Observatory
