To give you a better idea of the coldest time of year, on average, for your area, NCEI has created “Coldest Day of the Year” maps for the contiguous United States, Alaska, Hawaii, and Puerto Rico. The maps are derived from the 1991–2020 U.S. Climate Normals—NCEI’s 30-year averages of climatological variables including the average low temperature for every day. From these values, scientists can identify which day of the year, on average, has the lowest minimum temperature, referred to here as the “coldest day.”
The contiguous United States map reveals several interesting regional differences across the country. Most prominently, the portion of the United States west of the continental divide (the West) typically reaches its climatological coldest day in December, whereas most of the East reaches its seasonal minimum in January. The West is profoundly influenced by the flow of moderating air masses with clouds and precipitation coming off the Pacific Ocean and aligns more closely to the seasonal solar cycle, while the East is responding to cold air flowing south from Canada that is modified by snow cover reflecting solar radiation away from the surface.
Pockets of later coldest dates near the Rockies and Cascades/Sierra Nevada often correspond to stations located in deep valleys where calm winds and snow cover cause temperatures to become colder than nearby higher ground, a condition called a temperature inversion. Alaska tends to have January coldest day normals, while the low latitude islands of Hawaii and Puerto Rico can have normal coldest days later in February and even in early March.
Compared to the 1981-2010 version of this map, there has been a small but noticeable shift of the coldest day to dates 3–6 days later or more at many stations in the U.S. east of the Rocky Mountains. This is not surprising given that early winter warming is more pronounced than late winter warming between the new and previous Normals periods in this region. While the far northwestern U.S. also shows a shift of the coldest day to a later time, the rest of the western U.S. does not show a consistent pattern, with some stations actually shifting to earlier coldest day times.
Temperature Normals are important indicators used by many U.S. economic sectors for planning and making decisions for periods of time beyond the range of weather forecasts. Knowing the probability of low temperatures can help energy companies prepare for peak heating demand. They are also useful planning tools for the healthcare, construction, and tourism industries. You may even want to check the Normals before planning your next event or vacation!
While the map shows the coldest days of the year on average throughout the United States, this year’s coldest day may vary from the normal based on actual weather and seasonal climate patterns. For prediction of your actual local daily temperature, and to see how it matches up with the Climate Normals, check out your local forecast office on Weather.gov.
Also see the Climate.gov interactive map.