Coldest, Hottest Places Depend on What's Measured
The town or city in the continental United States that can lay claim to being the hottest or coldest location hinges on how temperature is calculated. The place most often having the highest temperature of the day for the 48 states is not the same place with the highest mean yearly temperature, for example.
Death Valley, California is the undisputed winner at reporting the most days with the highest temperature, achieving that distinction 803 times between April 1995 and March 2005. For the place with the highest mean yearly maximum temperature, Lake Havasu City in Arizona shares the honors with Death Valley at 90 °F. But none of the hottest spot winnings for these two sites occurred in December or January.
Top temperatures during winter mainly show up in Florida, with Fort Myers leading the way at 159 days, followed by Pembroke Pines with 71 and Naples with 61 days. Altogether 21 locations, mostly in California, Arizona, Texas and Florida, had the continental US's highest daily temperature over 50 times during the ten years. Key West, Florida holds the highest mean yearly temperature at 78 °F, coming in two degrees above Death Valley and Lake Havasu City.
The day's coldest place also depends upon the time of year, with 364 places winning that distinction during the decade. The coolest summer days often occur where the California ocean current moderates temperatures of coastal Oregon and Washington. Winter cold spots repeatedly show up in the northeastern US, particularly at Saranac Lake, New York on 128 days, and in Berlin, New Hampshire on 92 days. Other states with frequent cold spots include Wyoming, Colorado, Maine and Minnesota.
The town most often achieving the coldest temperature of the day is Stanley, Idaho at 398 days, mainly staying chilly during summer and autumn. West Yellowstone, Montana gets particularly frigid winters, bringing it 337 of the coldest days. But Darwin Ranch in Wyoming has the lowest mean yearly minimum temperature at 14 °F, considerably below Stanley's 18 °F and West Yellowstone's 21 °F.
Many of the coldest sites are high-elevation valleys that receive chilled air draining down the surrounding mountains. Yet the frostiest mean yearly temperature measured among the 48 states is 27 °F on a 6,262 foot peak: Mount Washington in New Hampshire.
Guy King. 2007. The Hottest and Coldest Places in the Conterminous United States. Yearbook of the Association of Pacific Coast Geographers. 69: 101-114.