Later Fall Frost Extends Allergy Season

Climate Central analysis of 204 U.S. cities shows that the first fall freeze is arriving later in 88% of locations, delaying the date by an average of 12 days since the early 1970s. This trend extends the growing season for ragweed, prolonging allergy seasons, and disrupts ecological cues for bird migration, hibernation, and fall foliage. Additionally, the delay affects the $27 billion U.S. fruit and nut industry by reducing necessary chilling periods and allowing disease-carrying insects like mosquitoes to persist longer into the year.

• Analysis of 204 U.S. cities reveals that the first fall freeze (minimum temperatures at or below 32°F) is now arriving later in 88% (179) of those cities, with an average delay of 12 days compared to the early 1970s.
• The most significant delays in the first freeze are observed in 70 cities, particularly in the Upper Midwest, Ohio Valley, and Northeast. The longest delays were recorded in Reno, Nevada (41 days), Bend, Oregon (38 days), Santa Maria, California (35 days), Toledo, Ohio (29 days), and Boise, Idaho (29 days).
• Warmer fall temperatures and delayed freezes extend the ragweed growing season, which typically peaks in September and lasts through October, thereby worsening and lengthening the fall allergy season.
• Climate warming is disrupting ecological and biological processes, including the timing of bird migrations, hibernation, and the development of fall foliage. It also allows disease-carrying insects, such as mosquitoes, to remain active longer.
• The U.S. fruit and nut industry, valued at nearly $27 billion, is impacted by delayed freezing; 181 U.S. locations have experienced a decrease in the sustained chilling period required for high-quality non-citrus yields since 1980.

APA

Climate Central (2025). Later Fall Frost Extends Allergy Season. https://www.climatecentral.org/climate-matters/later-first-freeze-in-179-US-cities

Chicago

Climate Central. Later Fall Frost Extends Allergy Season. 2025. https://www.climatecentral.org/climate-matters/later-first-freeze-in-179-US-cities.

Wikipedia

{{cite report |author=Climate Central |title=Later Fall Frost Extends Allergy Season |date=8 October 2025 |url=https://www.climatecentral.org/climate-matters/later-first-freeze-in-179-US-cities |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climatecentral2025later, author = {{Climate Central}}, title = {{Later Fall Frost Extends Allergy Season}}, institution = {Climate Central}, year = {2025}, month = oct, url = {https://www.climatecentral.org/climate-matters/later-first-freeze-in-179-US-cities}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }