The Second Snowfall

The Second Snowfall
Tuesday December 12, 2017

Today's snowfall is significant,
and here's why.

Have you ever experienced a winter in which the first snowfall occurs very early in the season, and then wondered if that was a harbinger of a bad winter? What about a slow-starting winter that left you wondering if the rest of the season would follow suite? Well that's one of the things I was recently thinking about, so I decided to crunch some numbers to see how snowfall dates relate to season total snowfall.

~ The First Snowfall ~

It was found that the first snowfall date is not a very good predictor of the total snowfall for the season. By plotting the date of the first snow and the total snowfall for the season over multiple years, we can get a relationship between the totals and the dates. We can then use this relationship to calculate any season's total snowfall based on the date of the first snowfall and compare it to how much snow actually fell. When we do this, if the average difference between the Calculated Season Totals and the Actual Season Totals is small, then the relationship is strong and start date is a good indicator of the rest of the season. If the average difference between the Calculated Season Total and the Actual Season Total is large, the the relationship is weak and start date is not a good indicator for the rest of the season. Overall, for the past 13 years, the average difference between Calculated Season Total and the Actual Season Total was 37 inches. This means that the average total snow prediction for the season using the date of the first snowfall would have been off by 37 inches. Because we normally see 43 inches of snow in one season, to be off by 37 inches is a lot, and so the first snowfall date is not a very good predictor of the total snowfall for the season.

~ The Second Snowfall ~

One of the problems with focusing on the first snowfalls is that they can easily be "outlier" events - that is, random snowfalls that are well removed from the rest of the season. The best example of this is from last winter: the first snow of the season happened during a random cold snap on October 27th, but then the next snowfall didn't occur until December 5th. To filter these outlier events, the date of the second snowfall of the season was evaluated as a predictor of season total snowfall utilizing the same process as with the first snowfall. Using the second snowfall date for the past 13 years, the average difference between the Calculated Season Total and the Actual Season Total was found to be 13 inches. This means that the average total snow prediction for the season using the date of the second snowfall would have been off by just 13 inches. Considering that we normally see 43 inches of snow in one season, to be off by 13 inches isn't terrible, and is much better than using the first snowfall date.

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Image caption: The chart shows the relationship between Calculated Season Total snowfalls and Actual Season Total snowfalls. The purple dots are the calculated totals using the first snowfall date, the green dots are the calculated totals using the second snowfall date, and the red line represents the Actual Season Total snowfalls. The closer the purple and green dots are to the red line, the more accurate the calculated predictions are.

~ What about this winter ~

Today's 1.2 inches of snow is significant because it marks the second measurable snowfall of the winter. We can now make a relatively informed prediction for the rest of the season using our second snowfall predictor. The Calculated Season Total for this winter is 48 inches of snow, and Kingstonsnows will be recognizing this as its official snow total prediction for the 2017-2018 winter season - its first season prediction ever. This is slightly above the 13-year average of 43 inches. Applying the average error of 13 inches to this value, we get a possible season total range of 35 to 61 inches. There is an 80% chance that the final total will fall in this range.

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We'll see how the prediction does in the spring!

-Ethan

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