Seasonal forecasting is a tough game, but as we're entering the winter season, there are some strong signals for how this winter may shake out.
Last winter was a snowy one. Portland totaled 95.3 inches, far above the average 61.9 inches. Bangor picked up 82.6 inches of snow, also above the average 66.1 inches.
There are many factors that influence a winter forecast. Different signals can conflict and make it difficult to draw a conclusion. When creating our forecast for this winter, it seemed like all of the data pointed to a common theme: More snow than average.
In our winter weather special, we focused on three of the elements that went into our forecast.
1) October was the warmest on record in both Bangor and Portland. If it weren't for a cooler November, this would easily go in the books as the warmest fall on record. As explored by Keith in a Brain Drops segment back in October, when evaluating the warmest Octobers in Bangor and Portland, 17 of the 20 following winter seasons produced above average snowfall. This wasn't only the case in Maine. A majority of the warm Octobers in Concord, New Hampshire were followed up by a snowy winter.
While a forecast for a snowy winter can't be made by these facts alone, we were able to see how this October fit into the larger scale weather pattern.
2) Some of those seasons were La Nina winters. Perhaps you've heard of El Nino - warming of ocean water off of South America in the Pacific Ocean. La Nina is the opposite - when the Pacific Ocean is cooler than average in that region of the world. Both influence weather patterns in the United States, rearranging the jet stream and storm tracks across the Northern Hemisphere.
La Nina is forecast to reach moderate status, possibly peaking mid-winter.
There have been four moderate La Ninas since 1950. Three of those produced much above average snowfall in Portland. The snowiest winter on record (1970-1971) was a moderate La Nina.
3) Ocean water temperatures are above normal off the northeast coastline. While this can tip air temperatures in a milder direction, it's a key to our forecast because it may add additional moisture and fuel for storms to grow and intensify. Coastal storms grow in a baroclinic zone, or where cold and warm airmasses come together. The added warmth could enhance this zone.
With all that in mind, the factors we considered heavily leaned in a snowy direction for Maine. Remember, a snowy winter isn't necessarily a cold one. All it takes are a couple of big ones to push us above the average.
Our outlook calls for above average snow in central and southern Maine. It's possible a more southern storm track could limit the amount of snow in northern Maine - but even there, close to average snow is expected.