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where the temperature in late December is frequently well below freezing. Second, there are plenty of places in the U.S.

It also means that at some locations, changes could be the result of natural decadal variability. This gradual introduction of a single decade of new data means that most changes from one Normals period to the next will be relatively small compared to the trend between the oldest decade and the most recent decade. From one 30-year Normals period to the next, two decades of the data are the same only one decade out of three is new. If you’re tempted to compare the two maps for signs of the influence of long-term warming, keep a few things in mind.įirst, comparing two adjacent Normals periods is not the most direct way to look for climate change. Long-time readers of will know that this map is an update of an analysis originally made by NCEI experts using data from the 1981-2010 U.S. These probabilities are useful as a guide only to show where snow on the ground is more likely. For prediction of your actual weather on Christmas, check out your local forecast at. While the map shows the historical probability that at least 1 inch of snow will be observed on December 25, the actual conditions in any year may vary widely from these because the weather patterns present will determine the snow on the ground or snowfall on Christmas day. This collection contains daily and monthly Normals of temperature, precipitation, snowfall, heating and cooling degree days, frost/freeze dates, and growing-degree days calculated from observations at nearly 15,000 stations, the majority of which are operated by operated by NOAA’s National Weather Service. The 1991–2020 Climate Normals are the latest three-decade averages of several climatological measurements.

See and download the background map here.

The observing network in Alaska is too sparse for scientists to interpolate with confidence, so the map includes only the station dots. (Sorry West Coast, Gulf Coast, Deep South!) White shows probabilities greater than 90 percent. Interpolating means estimating values where you don’t have direct observations, using existing observations and physical relationships, such as the way temperature is known to change with altitude.ĭarkest gray shows places where the probability is less than 10%.

The background map shows interpolated values for all locations in the Lower 48. The dots show the probability at specific weather stations. Climate Normals from NOAAs National Centers for Environmental Information (NCEI). The map above shows the historic probability of there being at least 1 inch of snow on the ground at weather stations across the United States on December 25 based on the latest (1991-2020) U.S.