Weather Recap

May 2026: Warmer and Drier Than Average

A near-record heat spike, a chilly close, and an unusual sonic boom — here’s what our instruments recorded on the summit this May.

A Warmer Month With Below-Normal Rainfall

May 2026 ran warm and unsettled. The approximated 24-hour mean temperature of 58.4°F came in nearly 3 degrees above the 130-year average for the month, with average highs of 68.9°F (+2.1° above normal) and average lows of 49.1°F (+0.9° above normal).

The third week of the month brought a scorching heat spike: 95°F on May 19 shattered the previous record for the date (91°F, set in 1962) by four degrees, making it the second-warmest May temperature ever recorded at Blue Hill and the second-earliest occurrence of such heat in the season. The month closed on a much colder note, dipping to 39°F on the 31st.

Rainfall was frequent but modest — 3.13 inches total, slightly below the 30-year normal, spread across fifteen measurable-precipitation days (plus six more trace days), with no dry stretch longer than two days. The heaviest 24-hour total, 0.89 inches, fell during a cold, breezy storm on the 29th–30th, which also produced the month’s peak wind gust of 56 mph from the north-northeast.

“A very unusual occurrence — the loud sonic boom of a meteor exploding roughly 40 miles east of the Observatory was heard in the vicinity shortly after 1 PM on May 30.”

141 years of daily observation — and counting.