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December 2024 Summary – Warmer and Wetter Than Average

January 1, 2025

Blue Hill Observatory December 2024 Summary: December temperature was above average with more rainfall and much more sunshine than expected. The approximated…

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Sunrise on the summit of Great Blue Hill on the morning of 21 December 2024 following a nine-inch snowfall the previous day. Photo by Blue Hill observer Joshua Polen.

Blue Hill Observatory December 2024 Summary:

December temperature was above average with more rainfall and much more sunshine than expected. The approximated 24-hour mean temperature for the month of 32.9 deg F was 2.8 degrees warmer than the 1891-2020 130-year average for December, and it was just 0.1 degrees warmer than the 1991-2020 30-year average. The average maximum temperature of 40.4 deg F was 0.2 degrees warmer than the 30-year normal, and the average minimum temperature of 25.5 deg F was 0.6 degrees warmer than the 30-year normal. After a cool start during the first week, December brought large swings in temperature, though there were no daily records. The highest temperature was 62F during a warm rain and wind storm on the 11th, and the lowest temperature was 4F on the 23rd, which was also the coldest temperature for the year. The mean water vapor pressure, which is an absolute measure of water vapor in the air, was 5.2 mb, which corresponds to a mean dew point of 29F, which was above average for the month. December brought relief from a summer to fall drought, and the month was the first with above average precipitation since June. The total precipitation for the month was 7.58 inches, which was 2.19 inches more than the 30-year normal. The greatest amount in 24 hours was 3.43 inches on the 11th-12th, and the calendar day total of 3.38 inches on the 11th was the third wettest day ever observed in December. Another significant storm brought 1.17 inches of liquid equivalent and the largest snowfall of the month of 9.4 inches on the 20th. The snowfall total for the month was 12.6 inches, which equalled the 30-year normal. There was one thunderstorm day during December during the heavy rain on the 11th, which was one more than average, and the annual total was 20, which was two fewer than average. A large area of high pressure moved into New England after the storm on the 11th, and the sea-level pressure at the Observatory peaked at 30.92 inches on the 14th, which was the highest pressure for the year. This reading was the highest sea-level pressure in December since 31.04 inches, the monthly record, was observed in 1949. It was also the highest pressure for any month since the station record sea-level pressure of 31.08 inches was measured on 13 February 1981. The mean wind speed was 11.9 mph, which was the third lowest on record for the month, and the prevailing wind direction was from the west. The highest wind gust was 65 mph from the south-southwest during the heavy rain on the 11th. Despite the high rainfall, December sunshine was well above average with 154.4 hours of bright sunshine, or 56 percent of possible, which was ten percent more than the long-term average for the month.

BHO Wettest December Calendar Days, inches (1886-2024):

1) 3.94 on 12 Dec 1992
2) 3.64 on 26 Dec 1969
3) 3.38 on 11 Dec 2024
4) 3.23 on 9 Dec 2014
5) 3.03 on 17 Dec 1888
6) 2.93 on 17 Dec 1973
7) 2.87 on 17 Dec 2000
8) 2.86 on 5 Dec 1993

BHO Highest December Sea-Level Pressure, mb (1885-2024):

1) 31.04 on 25 Dec 1949
2) 30.98 on 1 Dec 1887
3) 30.95 on 31 Dec 1889
4) 30.92 on 14 Dec 2024
5) 30.88 on 14 Dec 1893
6) 30.87 on 21 Dec 1942
30.87 on 23 Dec 1971

BHO Lowest December Mean Wind Speed, mph (1885-2024):

1) 11.2 in 2023
2) 11.8 in 2015
3) 11.9 in 2024
4) 12.0 in 2017
5) 12.1 in 2021
6) 12.2 in 2014
7) 12.3 in 2013

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
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