Defining What 'Winter' Means

Weeks before winter actually settles in meteorologists are called upon to make their predictions for what type of season it will be. Long-range forecasting is one the more difficult tasks for meteorologists (my profession), so we turn to climatologists to help us analyze and interpret worldwide weather patterns that affect us locally.

Typically when we speak of winter temperatures we usually mean average temperatures for the months of December, January, and February. When we talk about snowfall we usually mean the total snowfall for the entire season (September-May.) The average winter temperature for Grand Rapids is 26.8°F while the average snowfall is 74.9" (based on the 30-year average from 1981-2010).

Last Year's Forecast Results

Last year, I forecast the winter of 2011-12 would feature temperatures near to slightly below average (26.3°F, or -0.5°F);it turned out to be our third warmest winter in Grand Rapids with 32.2°F, or 5.4°F above average). I also predicted snowfall would be average or slightly above average (80", or +5.2"); it turned out to be a rather dry season in Grand Rapids with 51.2" or 23.7" below average).

ENSO Neutral

This year, the sea-surface temperatures over the Pacific Ocean are considered 'neutral' (neither La Niña nor El Niño). This means that other weather patterns such as the North Atlantic Oscillation (NAO) may play a larger role in shaping our winter season.

NAO Snowfall

Right now, the North Atlantic Oscillation is in the negative phase (NAO-). If this continues throughout the winter it would mean drier conditions (and less snowfall) over the eastern United States, including the Great Lakes. If the NAO turns positive (NAO+), wetter conditions will prevail (with more snowfall). Unfortunately, the NAO is not predictable beyond two weeks.

NAO Temperatures

Temperatures during the negative phase of the NAO are typically colder than usual, while during a positive phase temperatures are usually warmer than average.

Statistical Comparisons

To make a stronger case I analyzed the winters following the warmest summers on record, like this past summer (second warmest). Winter temperatures averaged 2.7°F colder than usual (24.1°F), with seven out of ten winters below average and with three out of ten winters above average. Season snowfall averaged 24.4" less than usual (50.5"), with nine out of ten winters below average and only one winter above average.

The Forecast

In general, I believe West Michigan will have a cold and dry winter, with temperatures that are below average (26.0°F, or -0.8°F for Grand Rapids); snowfall will also be below average (65", or -10" for Grand Rapids).