Dec 13, 2015

A statistical relationship between fall temperatures and winter snowfall

Warmer than normal average temperatures were recorded across Upstate New York during October and November 2015.  The month of November for Glens Falls was the 2nd warmest November on record and for Albany it was the 5th warmest November.

The NWS Albany, NY shows a comparison of monthly average temperatures over the past five years.

The Case Study for GFL

Onto the study: The study was modeled after one done for Boston by R.J. Panuto a former NWS meteorologist, I used the temperature and snowfall data for Glens Falls (GFL), NY The point of the study is to see if there is any correlation between the departure of average monthly temperatures for the month's of October and November and the upcoming winter's (December-April) snowfall departure. The hypothesis is: Warmer than normal fall temperatures lead to below normal snowfall. Colder than normal fall temperatures lead to above normal snowfall.

First the average monthly temperature for October (47.8°)  and November (37.5°) for GFL was computed. Next the average snowfall for December through April was computed. (Note that since October and November temperature data was used in this study the average monthly snowfall for these month's were removed from the total snowfall data for the winter season. These amounts were minimal and would not have any impact on the goal of the study). The average December through April snowfall for GFL is 64.6". (Note that the standard deviation for GFL's snowfall is around 18").

The graphs below are the average October and November temperatures and December through April for GFL for the period of record ( which is 1949-2015 for temperature data and 1949-2001 for snowfall. [Snowfall measurements ceased at the airport with the implementation of Automated Surface Observation Systems or ASOS].

Now a statistical analysis was done to see if there was a correlation between a warmer or colder than normal October or a warmer or colder than normal November and whether or not the following December through April snowfall was above or below normal. A third analysis was done comparing BOTH October and November temperature departures and the upcoming winter snowfall.

The image below shows the number of occurrences of BELOW or ABOVE normal temperatures for October and above or below normal snowfall.

The correlation for October is rather poor at best. Now let's move onto November's temperature departures and snowfall as shown in the next image:

As the graph above shows when temperatures are ABOVE normal for November there were a greater number of cases of BELOW normal snow (histogram on the left side) and when temperatures are BELOW observed snowfall seasons was ABOVE normal in a greater number of cases..

Lastly a comparison between BOTH months having the SAME temperature departure compared to the snowfall departure:

Once again a strong correlation shows up when BOTH months are ABOVE normal then snowfall is BELOW norma l(histograms on the left side of above image) . A similar inverse relationship exists for BELOW normal temperatures for both months and having ABOVE normal snowfall (histogram on the right side of above). However, this last analysis should be used with caution due to the small sample size.

Even though both the two months temperature departure compared to snowfall departure is with a limited number of cases, as well as the November temperature departure used by itself, there is strong significance of a correlation.

All in all the analysis I performed is similar to the results of the Panuto's work and I think that the correlation would probably hold true for other locations in Eastern NY State and New England as well. Also note that this study just gives a simple yes/no "forecast" as to whether or not snowfall will be above or below normal. It doesn't give a quantitative snowfall amount.

This years expected snowfall for Glens Falls (and Albany)?

Based on a very warm November 2015 and my study I would tend to go with BELOW normal snowfall for Glens Falls (and Albany) for the Dec 2015-Apr 2016 period.  Sorry snow lovers but then again there were some seasons that had above normal snowfall with a warmer than normal October, November, and both months together (not many though!)