The Definition of a Winter Season Duration

First Day of Winter represents a daily max temp equal or below 32°F and a snow depth of 1" or greater for several consecutive days.
                                
Last Day of Winter
represents a daily max temp equal or above 32°F and a snow depth less than 1" for several consecutive days.

In the case of OSNW3, six(6), is used for "several" consecutive days.

A graphical example is below. Use the links on the left hand side of the page to navigate to different decades. Slowly but surely past decades will be added to the output.