First Snowfall of the Year: Map Shows Median Dates A climatologist has created a detailed map illustrating the typical median dates for the first measurable snowfall across the United States, based on 45 years of historical snow records. The map, developed by Brian Brettschneider using data from NOAA’s Global Historical Climatology Network, identifies the median date for the first snowfall at each location with at least 20 years of complete snow data since the winter of 1980-81. This effort builds on NOAA’s Climate.gov analysis, which calculates the probability of measurable snowfall at any given location. Both datasets emphasize that latitude and elevation are the primary factors determining when snow arrives in a region. The map categorizes locations into nine color-coded bands, ranging from “before Sept. 15” to “after Dec. 31.” Northern Canada and Alaska’s interior fall into the earliest bands, with some areas experiencing their first snowfall before mid-September. Conversely, the Gulf Coast, Deep South, and Desert Southwest are in the latest bands, with parts of Texas, Florida, and Southern California lacking enough snow events to produce a reliable median date. Elevation also plays a critical role, as high-altitude areas like the Rockies face a year-round snow risk, while low-lying valleys may wait until November or December for their first snowfall. Geographic factors further complicate the timing of the first snowfall. The Plains and Midwest do not follow a clear east-west pattern, with early snow pushing farther south through the high Plains than across the Midwest at the same latitude. This is attributed to the Rockies channeling cold Canadian air down the Plains ahead of seasonal storms.#el_nino #noaa #brian_brettschneider #climate_gov #global_historical_climatology_network
