Official 2014-2015 Winter Forecast Summary

This is the summary of the SWCTWeather official forecast for the winter. This basic summary is just meant to give a first glimpse into expected conditions of the winter, with many more details coming in future posts. The winter forecast is created through a number of statistical forecasts, indicators, and correlations, stemming primarily from climatological factors such as pacific ocean temperatures, stratospheric winds, and the like. We combine these weaker correlations to attempt to find an overall view of the most probable winter conditions. Of course, with any number of variables in every season, it is impossible to predict with complete accuracy any scenario. Using climate variables, we can essentially find what is more likely every winter season, and come to some broad conclusions regarding individual variables. We then combine these broader conclusions with different random observations throughout the historical data sets we use to find the general trends published.

This year, we are publishing a slightly modified version of the winter forecast: we are giving a probability of different various snowfall amounts and temperature differentials based on our observed trends. We will list the latest official forecast here, and then give an explanation as to what drove some of the forecast. However, since this is just the basic summary, we will just provide a general overview of our thoughts, and the in-depth technical analysis will come later.

SNOWFALL

Less than 10 inches of snow: 15%

Less than 20 inches of snow: 35%

Less than 30 inches of snow: 65%

Less than 40 inches of snow: 80%

Less than 50 inches of snow: 90%

More than 50 inches of snow: 10%

TEMPERATURE

Temperatures more than 1 degree above average November-March: 50%

Temperatures within 1 degree of average November-March: 30%

Temperatures more than 1 degree below average November-March: 20%

These forecasts are based off of a base of Bridgeport, CT. The surrounding area will likely see more snow as Bridgeport will often report slightly less snow due to the urban heating effect, and inland areas of Westchester, Fairfield, and New Haven counties historically see significantly more snow as the cold low level air gets locked in longer. With an average of around 28 inches of snow per season, the going forecast is for a winter with less than average snowfall and above average temperatures not just for Bridgeport but for the entire forecast region.

A number of different indicators were taken into play when creating this forecast, and for those that enjoy the snow and the cold (often those most involved in predicting the weather) forecasts such as these are normally not taken too well. Meteorologists use any number of indicators for a forecast; the main ones used here were ENSO (El Nino/La Nina and Pacific Ocean temperatures) along with the QBO (stratospheric winds) and other climate and longer-run indicators.

It is important to note that there are multiple historical winters that exhibit strong similarities to the upcoming one. The strongest analog was the winter of 1968-1969, with almost exactly the same ENSO conditions and formation as we are observing now. Sadly QBO data is not widely available from that time frame to access. That winter season saw average snowfall with slightly below average temperatures. The second strongest analog was the winter of 2012-2013; this winter has a very similar QBO set-up and is one possible ENSO track. As most remember, that winter had above average snowfall alongside slightly above average temperatures.

Some central technical assumptions for the winter were a weak El Nino (DJF ENSO value around .6 or .7), which is essentially in line with the daily updates from the Climate Prediction Center. Similarly, a negative QBO value will dominate the winter; this combination will help drive a slightly above average PNA value although the NAO and AO will oscillate.

When going through the weighted snowfall forecast, a base of 21.5 inches of snow was found for Bridgeport; approximately 23% below seasonal snowfall. It is expected that there will be a period in time that is snowy this winter; historically speaking there will be a time frame with a positive PNA and a negative NAO that is conducive for snowfall. Most storms in patterns like this tend to be smaller rather than larger, with a week or two with a couple small snow events moving through. However, the one thing that is worth watching out for, which occurred in 2012-2013, is that the lack of major storms can prime the pattern, via warmer ocean temperatures, etc. for an extreme snow storm. This does not occur very often, but a couple analogs did indicate the potential for significantly above average snowfall. It will be important through the winter to continue to monitor the potential for larger snow events, especially later in the winter, as it is far from impossible.

Finally, just statistically speaking, with the past two winters in Bridgeport having seen over 50 inches of snow, there is no time in recorded meteorological history there (since 1949) that there were two winters in a row where that happened. Having a third is even less likely. Typically, snowfall oscillates with the QBO, which changes every year or two and can prevent back-to-back exceptionally severe winters. Due to “Nemo” in 2012-2013, that wasn’t the case; it’s more likely now that we revert back to the mean. The 10, 20, 30, 40, and 50 year moving averages for snowfall are all above the climatological mean, meaning that we have been in a much snowier pattern the last decade or too. This pattern may help us reach slightly elevated snowfall levels and get close to average even in an atmospheric pattern that is not all that favorable; the forecast basically gives us around a 35% chance of achieving average snowfall across the region. While completely possible, the current thinking is that it is more likely that we just fall short.

There are plenty more data points and analysis to come, but we had promised a basic summary of the winter forecast at a reasonable date, and as soon the data analysis was completed we wanted to publish the preliminary findings here. We will continue to publish more technical discussions, though the most detailed winter forecast will only be able available to clients by the end of the month. Please stay tuned as the publishing of the winter forecast traditionally signifies consistent site updates and storm coverage through the Fall season.

Additionally, we are pleased to announce that we will be launching a premium subscription service tentatively on November 1st. For a reasonable monthly or yearly fee, we will provide additional meteorological services beyond what we have historically served in the past, along with additional impact forecasts. We will be posting polls to sign up and receive email updates when the service becomes available and goes live, as we are also looking to gauge interest in the advanced weather services. Free services will still of course be offered through the winter here as well, but the premium website is a chance to receive more regularly updated content that goes more in depth with all of the storms. More information will be available on this in the coming weeks.

Thank you for reading our 2014-2015 winter forecast overview and we look forward to serving you through the coming season.

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