Extreme Weather Events: Which Counties Are Most Affected?

Extreme weather shapes where Americans choose to live, what they pay for insurance, and how local governments allocate emergency resources. While media coverage tends to focus on individual storms, the underlying climate data reveals which counties face the most persistent extreme conditions year after year.

Using NOAA's 30-year climate normals, we identified the counties most affected by three types of weather extremes: excessive heat, heavy snowfall, and dramatic seasonal temperature swings.

Counties with the Most Extreme Heat Days

Extreme heat — defined as days where the temperature exceeds 90°F — is the deadliest weather phenomenon in the United States. The counties with the most extreme heat days are concentrated in the desert Southwest, the Central Valley of California, and the Deep South.

Starr County, TX leads with an average of 191 extreme heat days per year — that is more than half the calendar year above 90°F.

Counties with the Most Snowfall

Heavy snowfall affects transportation, infrastructure costs, and daily life. The snowiest counties are found in the Great Lakes snow belt, the northern Rockies, and high-elevation areas of New England.

Counties with the Biggest Seasonal Temperature Swings

Some counties experience enormous temperature differences between summer and winter. The Great Plains and upper Midwest are notorious for this — counties where January averages are below 10°F and July averages exceed 80°F, creating swings of 70°F or more.

What This Means for Residents

Extreme weather conditions have direct financial implications for residents:

• Energy costs: Counties with extreme heat or cold face significantly higher utility bills. Air conditioning in a 150+ heat-day county can add hundreds of dollars per month to summer bills.
• Insurance premiums: Counties prone to extreme weather events often face higher homeowner's insurance rates, particularly for wind, hail, and flood coverage.
• Infrastructure maintenance: Heavy snowfall counties spend more on road maintenance, snow removal, and building upkeep. Property owners face additional costs for winterization.
• Health impacts: Extreme heat increases risk of heat stroke and cardiovascular events. Extreme cold increases risk of hypothermia and respiratory illness. Both extremes disproportionately affect elderly and low-income residents.

Methodology

All data comes from NOAA National Centers for Environmental Information (NCEI), using the 1991-2020 U.S. Climate Normals. Extreme heat days are defined as days where the maximum temperature exceeds 90°F. Snowfall is total annual accumulation in inches. Temperature swing is the difference between average July and average January temperatures. Approximately 89% of US counties have sufficient station data for reliable climate normals.