The National Oceanic and Atmospheric Administration (NOAA) has released the schedule of the first dates of snowfall for this upcoming winter season.
According to the environment agency, the snowfall forecasts were based on the dataset for climate normals, or 30-day average, regularly used by the National Centers for Environmental Information (NCEI) to draw daily weathercasts.
Climate experts at the NCEI have created a historical map that outlines the projected first day of snow for an average year.
While it does not represent the actual average date that the first snowfall can be observed, the map instead highlights the first date by which there is a 50 percent chance at least 0.1 inch of snow will have amassed.
It was based on previously recorded patterns from 1981 to 2010, with minor adjustments in consideration of statistical noise included in the data.
The two main features on the map that influence the average of first snow are the altitude and latitude of a specific point.
People living in higher elevations and more northern areas are more likely to experience the threat of first snow at an earlier date. The agency's stations located in the Rockies, in fact, experience the threat of snow all year-round.
Meanwhile, stations in southern areas, such as Hawaii, the Deep South, the Desert Southwest and the Gulf Coast, very rarely experience any snowfall. Climate events in these areas do not occur frequently enough to collect any robust statistics.
Other regions experience more subtle but note-worthy snowfalls such as in the Midwest and across the Plains, where snowfall tend to follow a slightly northeastward tilt instead of the usual straight-up pattern of moving from east to west.
Scientists believe this phenomenon is more closely associated with the movement of cold air than elevation.
Mild plumes of earlier dates can also be seen on the map forming south of the Great Lakes. This shows how the northerly winds of fall can accumulate significant moisture from the warm lakes, resulting in an early start to winter precipitation every year.
Some parts of upstate New York and Michigan have already experienced this phenomenon this year.
Photo: Ralph Hockens | Flickr
