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May 2026 Summary – Warmer and Drier Than Average

June 3, 2026

Blue Hill Observatory May 2026 Summary:  May 2026 was generally warm with below average precipitation, snowfall and sunshine. The approximated 24-hour mean…

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NOAA GOES-19 visible satellite imagery of a chilly rainstorm over New England on the afternoon of Saturday, May 30th, 2026 at 1811 UTC with overlaid data (color contours) from the Geostationary Lightning Mapper (GLM) instrument depicting lightning to the south of New England and the bright flash of an exploding meteor over Cape Cod Bay.

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 56 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

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Blue Hill Observatory & Science Center · Legal

Data Use & Privacy Policy

Please read the full Policy before accessing Observatory data · Effective January 1, 2025

Notice: By accessing, downloading, or using any Blue Hill Observatory data or services, you unconditionally accept and agree to be bound by this Policy in its entirety. If you do not agree, you may not access or use Observatory data.
Effective January 1, 2025 · Milton, Massachusetts · bluehill.org
Part I — Data Use Policy
§ 01

Ownership and Proprietary Rights

All observational records, compiled datasets, metadata, database structures, and related materials provided by the Blue Hill Observatory & Science Center are the exclusive property of the Blue Hill Observatory & Science Center. The Observatory has maintained continuous weather observations at the summit of Great Blue Hill since 1885, and the entirety of that record — its compilation, structure, curation, and organization — constitutes a proprietary database protected under applicable United States law, including copyright law and common law database protections.

All rights not expressly granted in this Policy are reserved by the Observatory. No access to or use of Observatory data shall be construed as a waiver of any rights or as a license to use data beyond the scope expressly stated herein.

§ 02

Governing Law and Jurisdiction

This Policy shall be governed by and construed in accordance with the laws of the Commonwealth of Massachusetts, without regard to its conflict of law provisions. For interactions with international users, this Policy shall apply to the maximum extent permitted by applicable local law.

Any dispute arising from or related to this Policy shall be subject to the exclusive jurisdiction of the state and federal courts located in Norfolk County, Massachusetts. By accessing Observatory data, all users consent to personal jurisdiction in Massachusetts and waive any objection to the venue or inconvenience of such forum.

§ 03

Permitted Uses

Observatory data are made available for the following limited, non-commercial purposes only:

  • Personal study and analysis
  • Educational classroom use
  • Student projects
  • Non-commercial academic research
  • Publication of analyses, figures, models, or conclusions derived from the data, subject to the attribution requirements of Section 4

All other uses require prior written authorization from the Observatory.

§ 04

Attribution Requirement

Any use of Observatory data in any published, presented, or publicly distributed work must include the following verbatim acknowledgment:

“Data provided by the Blue Hill Observatory & Science Center, Milton, Massachusetts. Continuous weather observations since 1885.”

Failure to include proper attribution is a material violation of this Policy.

§ 05

Prohibited Uses

Unless explicitly authorized in writing, Users may not:

  • Resell, license, sublicense, or commercially exploit Observatory data in any form
  • Redistribute the dataset in whole or in part to any third party
  • Publish the dataset for download by third parties
  • Host, mirror, or archive the dataset on any external website, repository, or storage service
  • Upload the dataset to any public or institutional data repository
  • Provide the data through APIs, automated services, or subscription platforms
  • Incorporate the data into any commercial product, software, application, or service
  • Use the data for AI or machine learning systems intended for commercial use or external distribution
  • Use the data to create derivative datasets that enable reconstruction of the underlying observations
§ 06

Commercial Licensing

Organizations seeking to use Observatory data for commercial purposes must obtain a license prior to any such use. Licensing inquiries: data@bluehill.org.

§ 07

Automated Access

Automated scraping, bulk harvesting, or systematic downloading of Observatory data is strictly prohibited without prior written authorization.

§ 08

Enforcement and Remedies

Violation of this Policy may result in immediate revocation of data access, pursuit of legal remedies available under United States law, and referral to applicable authorities. The Observatory reserves all rights to seek injunctive relief, damages, and attorneys’ fees in connection with any unauthorized use of its data.

Part II — Privacy Policy
§ 09–10

Scope & Information Collected

This section governs the collection, use, storage, and disclosure of personal information from visitors to the Blue Hill Observatory website and users of its data services. The Observatory may collect contact information (name, email, organization) when voluntarily submitted, usage data including IP addresses and pages visited, and data download records.

§ 11–12

How We Use Information & Retention

Information is used solely for: responding to inquiries and licensing requests; monitoring and enforcing compliance with this Policy; improving website performance; and communicating Observatory news to opted-in users. The Observatory does not sell, rent, or share personal information with third parties for marketing purposes. Data access records may be retained indefinitely for compliance and enforcement purposes.

§ 13

International Users and Data Transfers

The Observatory is located in the United States. International users acknowledge their information will be processed in the United States under U.S. law. Users requiring specific data processing agreements under non-US law must contact data@bluehill.org before accessing data.

§ 14–16

Cookies, Security & Children’s Privacy

The Observatory website may use cookies for analytics and functionality. By continuing to use the site, users consent to cookie use. The Observatory implements reasonable measures to protect personal information but cannot guarantee absolute security. Observatory data services are not directed at children under 13.

Part III — General Provisions
§ 17–20

Modifications, Severability, Entire Agreement & Contact

The Observatory reserves the right to modify this Policy at any time. Updated versions will be posted at bluehill.org. Continued use of Observatory data following any modification constitutes acceptance of the revised Policy. This Policy constitutes the entire agreement between the User and the Observatory. Questions and licensing inquiries: Blue Hill Observatory & Science Center, Milton, Massachusetts — data@bluehill.org

By accessing, downloading, or using any Blue Hill Observatory data or services, you acknowledge that you have read, understood, and agree to be bound by this Policy.
Effective January 1, 2025 · Blue Hill Observatory & Science Center · Milton, Massachusetts