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A few locations saw their first measurable snow of the season this morning, while other folks may be wondering when they can expect to see their first accumulating snow?  Using history as a guide, we can get an idea of the first snowfall climatology for eastern Kentucky, and it's no surprise that elevation is a key factor in determining when you can expect that first measurable snow to occur.

Let's take a look at the first snowfall climatology for a few of our observing sites, NWS Jackson, Farmers 2S (otherwise known as Cave Run Lake Dam) and Williamsburg, using a "box and whisker" approach.  For the purposes of this study, measurable snowfall is defined as the date of the first tenth of an inch of snow measured at a given site.

The "box and whiskers" diagrams shown above graphically depict the first measurable snowfall climatology by showing the median date, interquartile range, outer range, and the climatological extremes for the given observation sites.  The median date shown is the middle observation in the dataset.  The interquartile range, shown by the box, is the central half of the data.  In other words, there is a 50% chance that future first snows will fall within this range of dates.  The outer range, depicted by the whiskers, depicts the 10th and 90th percentile dates.  The 10th percentile date means that there is a 10% probability that future first snows will occur before that date and the 90th percentile date means that there is a 10% probability that future first snows will occur after that date.  Finally, the earliest and latest occurrence of measurable snow found in the dataset at each site is depicted. 

It is important to note that while Farmers 2S and Williamsburg have snowfall records dating back over 100 years, this dataset only included the 35 years beginning in 1981, when snowfall records began at NWS Jackson.

Snowy scene from Breathitt County, January 2016
(photo courtesy of Tony Edwards)

Because of a higher elevation, we typically see the first measurable snow here at the NWS office near Jackson about 2 weeks before valley locations see their first snow.  The data also shows that latitude matters.  The first snow of the season typically occurs up north at Farmers before it occurs down south at Williamsburg, despite Farmers being at a lower elevation. 

Based on this study, there is a 50% chance that future first snows at NWS Jackson will occur between November 16th and December 14th.  However, down in the valleys where most east Kentuckians live and work, that first snow of the season is more likely to occur between December 2nd and December 31st according to the Farmers and Williamsburg data, with a median date between the 13th and the 15th.

Finally, it is interesting to note that there is around a 25% chance in any given winter that the first snow of the season won't occur until after the new year begins in the valleys while that has only happened once at NWS Jackson, during the winter of 2015/2016.  Amazingly, no measurable snow was recorded during the winter of 1991/1992 at Williamsburg.  While several trace snow events occurred during that winter, none measured a tenth of an inch or more.

So, that's a look at a statistical approach to forecasting our first measurable snow.  Will Mother Nature perform as expected this winter?  Only time will tell...