Shrinking Cold Snaps

KEY CONCEPTS

• From 1970 to 2021, 97% of the 244 stations analyzed have experienced shrinking winter cold snaps. 

• Cold snaps shrunk by 6 days on average across all 244 stations since 1970.

• Warmer winters in general and shorter cold spells in particular come with consequences that extend into the spring and summer.

With the news of last year being the sixth hottest for the planet and fourth hottest for the U.S., heat has been getting a lot of attention recently. But in the midst of winter, many wonder how warming trends are affecting the cold. This week we look at the changing length of winter’s longest cold snaps locally from 1970 to 2021.

But first: what’s a ‘cold snap?' We define a cold snap at the maximum number of consecutive days each year with temperatures below the 1991-2020 winter normal at that location. Climate normals are 30-year temperature averages that represent typical climate conditions for a given location at the annual, seasonal or monthly scale. Learn more about changing seasonal normals here.

Nationwide trends. From 1970 to 2021, 97% of the 244 stations analyzed have experienced shrinking winter cold snaps. During this same period, annual average temperatures increased for 98% of U.S. locations.

Shorter snaps. Across all stations, the longest cold snaps shrunk by six days on average. A third of all stations have seen their longest winter cold snaps shrink by at least one week since 1970.

Record locations. Las Vegas, Nev. has experienced the largest change with a reduction of three weeks, followed by Peoria, Ill. and Topeka, Kan., where cold snaps shortened by two weeks.

Exceptional locations. Although the vast majority of stations have trended toward shorter winter cold snaps, six stations saw no trend and three saw their longest cold snaps increase by 2-3 days (Marquette, Mich., Eureka, Calif., and Idaho Falls, Idaho).

Cold spells consequences. Why do shorter cold snaps matter? First, they’re yet another sign of our warming climate. Across the U.S. winter is the fastest warming season. So, even though the highest highs of summer tend to get the most attention, the warming lows of winter are an equally important trend, and one with wide-ranging consequences—the second reason cold snaps matter. Warmer winters in general and shorter cold spells in particular come with consequences that extend into the spring and summer.

• Periods of consistent cold can keep the populations of disease-carrying pests like mosquitoes and ticks in check.

• They’re also critical for building and maintaining the snowpack that provides much of the nation’s water supplies for drinking, irrigation and industry.

• Speaking of irrigation, extended cold periods are also key to the growth of crops that require winter chill for spring and summer fruit production.

• Winter recreation, which contributes to many regional economies and cultures around the country, also faces risks from shorter, warmer winters.

POTENTIAL LOCAL STORY ANGLES

How is climate change impacting winter activities and tourism near you? Climate Central’s report On Thin Ice covers the impacts of warming winters on America’s cold-weather sports economy.

Tools for reporting on winter weather events near you: Warmer temperatures can make winter storms more complicated, with sleet and freezing rain. Criteria for winter storm watches, advisories, and warnings can vary by region so check out your local National Weather Service office. The NWS also provides helpful information on how to stay safe in winter conditions, wind chill charts, and an explanation of the polar vortex.

LOCAL EXPERTS 

The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on winter warming. The American Association of State Climatologists is a professional scientific organization composed of all state climatologists. 

NATIONAL EXPERTS 

• Mary Stampone, PhD
  New Hampshire State Climatologist and Associate Professor 
  University of New Hampshire
  Contact: Mary.Stampone@unh.edu
  Expertise: Regional climate variability and change

• Judah L. Cohen, PhD
  Director of Seasonal Forecasting
  Atmospheric and Environmental Research
  Contact: jcohen@aer.com
  Expertise: Seasonal forecasting

• Mathew Barlow, PhD
  Professor, Environmental Earth and Atmospheric Sciences
  University of Massachusetts Lowell
  Contact: Mathew_Barlow@uml.edu
  Expertise: Climate variability and change

METHODOLOGY

The maximum number of consecutive days below normal was calculated for each winter season (December - February) from 1970 to 2021 using data from the Applied Climate Information System and the 1991-2020 NOAA/NCEI average temperature normals. The change in length of the average longest winter cold snap since 1969-70 was rounded down to reflect the change in whole days. Note that data in previous versions of this analysis may look different as the 1981-2010 NOAA/NCEI normals were used in previous versions of this analysis.

Climate Central's local analyses include 247 stations. However, for data summaries based on linear trends, only 244 stations are included due to data gaps in Dothan, Ala.; Hazard, Ky.; and Wheeling, W.Va.