The preliminary 2012-2013 Winter Forecast is out for the region, and all signs are pointing towards a winter with above average snowfall. However, this is not expected to be an extremely snowy winter, and it is highly unlikely that we approach record levels. The new winter snowfall forecast calculator I developed this year does indicate that there is a statistically significant chance of an above winter, and develops a range of total winter snowfall from 32-43 inches. The average winter in Westport, CT would bring just about 30 inches. This all stems from a calculated baseline of 37.41 inches of snow, which is the number that the updated forecast model gave.
The forecasting model consists of all winters dating back to the winter of 1949-1950, with each winter being weighted according to how similar the pattern was then to now. Of course, no winter is the same, which is why this forecast is only a guideline stating the overall trend of the winter. But history and climatologists have shown us that winter patterns repeat themselves, which is why these winter analogs are used. The first main indicator used in this forecast was what the ENSO value was, or what is more commonly known as El Niños/La Nina values. These form based on water temperatures in the central Pacific Ocean, which can determine global weather patterns. It is hard currently to forecast what exactly ENSO values will be for the winter, which is why an updated forecast will be released in early November, but preliminary observations point towards a weak El Nino, or warm Pacific water temperatures just below El Nino levels.
Averages of all winters where Pacific water temperatures were above average or where El Niños were in effect showed nothing statistically significant, and winters with ENSO values between .3 and .7, which is what looks most likely this winter, also did not show anything significant. However, when winters with those ENSO values appeared after La Ninas or when El Niños were forming (like this year) rather than weakening, it was determined that winters can be expected to be above average greater than 90% of the time. This is one of the main factors that resulted in the forecast for a winter above average. The final indicator was that winters back through 1949 also signified a winter with above average snowfall, sealing the forecast.
Two winters that were weighted the most in the foreacst were the winters of 2003-2004 and 2009-2010. The winter of 2003-2004 shows up because the ENSO value and overall pattern that year were extremely similar to what is forecasted this year, and that winter the area saw around 60 inches of snow. The winter of 2009-2010 showed up not because it was also an El Nino winter, even though it is, but because the blocking in the atmosphere that year was similar to that of what is expected in the coming year, meaning that storm patterns and storm strength were similar between the two years. Many may remember this winter as the winter of “snowmageddon”, where even though Westport barely saw above average snow (around 31 inches to be exact), Washington DC saw back to back storms that each approached the two-foot mark. As of right now, this winter does not look to approach the extremes of those winters, but the potential is there for one with fairly large storms, especially coastal Nor’ Easters with strong winds and heavy snow. A pattern with slow moving, strong storms is significantly more likely than last year, where my winter forecasted stated that the majority of winter storms would be fast moving and there would be few, if any, large Nor’ Easters.
The winter forecast last year, should anyone remember, was a fairly large bust, as were many others. On reanalysis of where the forecast last year went wrong, I found that many aspects of the forecast played out, such as a warmer winter and faster moving storms, but the difference lay in the teleconnections or blocking indices, which determine storm track and direction. These were not forecasted correctly, as it is almost impossible to forecast them months ahead, and that is what blew the entire forecast in terms of snowfall. To account for that this year, forecasts involving teleconnections played a much smaller role, and the overall weighted forecasted was only part of the winter forecast, further lessening the role of teleconnections and replacing the winter more with ENSO pattern forecasts, which are much easier to forecast.
Overall, the new winter forecast model used to weight winters and predict overall snowfall has been improved upon since last year, increasing reliability in the forecast. The forecast calls for between 32-43 inches of snow this year, with the model giving us a specific forecast of 37.41 inches of snow in Westport, CT, or about a 25% increase across the board throughout Southwestern Connecticut. This was based off of winters with weak El Ninos or Pacific Ocean temperatures above average but below El Nino conditions. This winter is forecasted to be around normal temperature-wise, but it is often even harder to forecast specific temperatures than overall snowfall or storm patterns. For more information on the winter forecast and a more detailed explanation of the forecasting model, along with a month-by-month analysis, a comprehensive forecast will be posted on my website at swctweather.wordpress.com by October 7th. This forecast will be updated in early November with the latest information, so make sure to stay tuned as we enter into what looks to be an exciting winter season.