Recently, NOAA released a map whose data points indicate the likely first day of snowfall for locations across the country. The map is very detailed (with the exception of Alaska being left out) and gives us skiers an idea of where to find early season turns across the West.
A quick look at the map reveals the obvious: the main factors that govern the average day of your first snow are the same main factors that govern your other major climate characteristics: latitude and altitude. In general, the farther north you are, and the farther up you are, the earlier the threat of first snow. In fact, the highest elevation stations along the spines of the Rockies have a year-round threat of snow.- NOAA Derek S. Arndt
However, one set of data points shows a startling fact.
Snowfalls are happening later and later each year (especially in Yakima, WA) as seen in the figure below. However, those data points are apparently contradicted by those in nearby Pendleton, Oregon, which show no apparent correlation between the onset of climate change and later snowfall dates.
On the other side of the United States, NOAA shows us how irregular Boston’s recent stormy winters have been and how the sports capital of New England is receiving snowfall earlier and earlier each year.
“So there you have it, a deeper look at our annual first date with snow. Much like a first date of the other variety, these first dates can be a little unpredictable, a little sensitive to where they occur, and a lot unaware of the big world going on around them.”– NOAA Derek S. Arndt
NOAA Disclaimer: This map isn’t the average date of the first observed snowfall. Technically, it’s the date by which there’s a 50% chance at least 0.1” of snow will have accumulated. It’s based on historical patterns from 1981-2010, with some “smoothing” to account for statistical noise in the data.
You can read the entire NOAA article here: First Dates (Beyond the Data)