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July 2021 Summary – Second Wettest on Record

August 5, 2021

Blue Hill Observatory July 2021 Summary: July was very cool and very wet with much less sunshine than average, and July set…

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Blue Hill Observatory July 2021 Summary:

July was very cool and very wet with much less sunshine than average, and July set a new record for the greatest number of days with measurable rainfall in any month. The 24-hour adjusted mean temperature for the month of 67.9 deg F was 2.1 degrees cooler than the 1891-2020 130-year average for July, and it was 3.8 degrees cooler than the 1991-2020 30-year average. The contrast between the July mean temperature and the warmest June on record that preceded it was so extreme that July was 2.1 degrees cooler than the 70.0 degrees observed in June, which was the largest negative difference in July-June mean temperature on record. This was also only the second time since 1885 that July was cooler than June with the other negative difference occurring in 2001. The average maximum temperature of 76.3 deg F was 3.9 degrees cooler than the 130-year mean, and this mean was the tenth coldest average maximum for July on record and the lowest since 2000. The average minimum temperature of 61.3 deg F was just 0.4 degrees cooler than the 130-year mean. The highest temperature observed all month was 90F on the 16th, which was the only 90-degree day all month, and the lowest temperature during July was 52F on the 31st. July total precipitation was extreme at 11.59 inches, which was 7.97 inches more than the long-term 130-year average and more than eight inches greater than the 1991-2020 30-year mean. The July total rainfall was the second highest on record for July and the greatest amount in a single month since 12.11 inches was observed in June 2013. Nearly ten inches of the rainfall fell during the first twelve days of the month, which included four calendar days with more than an inch of rain with one of these totaling 3.02 inches on the 9th. Two of these days set new daily records, including 1.49 inches on the 2nd, which surpassed 1.42 inches in 1986, and 1.98 inches on the 3rd, which surpassed 1.36 inches on that date in 1985. The greatest precipitation in 24 hours was 3.09 inches on the 9th-10th. The greatest rainfall in a single hour was 0.94 inches early in the morning of the 2nd. Rainfall was so frequent that there were 24 days with measurable precipitation, which was a new record for July and for any month of the year. There were ten thunderstorm days during July, which was five more than average, and the annual total through July has climbed to 19. This was the first month with ten thunderstorm days since ten were observed during June 1998. A thunderstorm during the evening of the 7th was severe with one-eighth inch diameter hail, frequent lightning and a peak wind gust to 63 mph from the NW, which was the highest wind gust for the month The mean wind speed for the month was 9.7 mph, which was the second lowest on record for July, and the prevailing wind direction was from the northeast. With all the precipitation, July sunshine was well below average with 192.9 hours of bright sunshine, which was 43 percent of the possible sunshine and 15 percent less than the 130-year mean. This amount was the seventh lowest sunshine on record for July at the Observatory and the lowest since 1967.

BHO Smallest July-June Mean Temperature Difference, deg F (1885-2021):

1) -2.1 / 70.0 / 67.9 in 2021 (July-June / June / July)
2) -0.9 / 68.5 / 67.6 in 2001
3) +0.7 / 64.8 / 65.5 in 1895
4) +1.0 / 65.8 / 66.8 in 1923
   +1.0 / 68.3 / 69.3 in 1930

BHO Coldest July Average Maximum Temperature, deg F (1885-2021):

1) 73.2 in 1914
2) 73.9 in 1891
3) 74.0 in 1902
4) 74.3 in 1889
5) 75.0 in 1895
6) 75.3 in 1888
7) 75.8 in 1906
8) 76.1 in 1915
9) 76.2 in 2000
10) 76.3 in 2021

BHO Greatest July Precipitation, inches (1885-2021):

1) 11.67 in 1938
2) 11.59 in 2021
3) 10.68 in 1988
4) 10.43 in 1921
5) 9.52 in 1915
6) 8.47 in 1889
7) 7.62 in 2009
8) 7.55 in 1916

BHO Greatest July Number of Days with Measurable Precipitation (1886-2021):

1) 24 in 2021
2) 20 in 1906
3) 19 in 1916
4) 18 in 1938
   18 in 1988

BHO Greatest Monthly Number of Days with Measurable Precipitation (1886-2021):

1) 24 in July 2021
2) 22 in December 1972
3) 21 in May 1888
   21 in May 2019
5) 20 in July 1906
   20 in April 1912
   20 in October 1913
   20 in June 1916
   20 in April 1929
   20 in January 1950
   20 in May 2005
   20 in April 2019
   20 in October 2019

BHO Lowest July Sunshine, hours (1885-2021):

1) 165.5 in 1916  [37%]

2) 183.0 in 1938  [41%]

3) 189.2 in 1958  [43%]

4) 189.5 in 1967  [43%]

5) 189.9 in 1927  [43%]

6) 192.0 in 1921  [43%]
7) 192.9 in 2021  [43%]
8) 195.7 in 1897  [44%]

BHO Lowest July Mean Wind Speed, mph (1885-2021):

1) 9.6 in 2019
2) 9.7 in 2021
3) 9.8 in 2012
   9.8 in 2020
5) 10.0 in 2017
6) 10.1 in 1906
   10.1 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

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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
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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
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§ 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

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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

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Part III — General Provisions
§ 17–20

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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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