As the 2011/2012 snow season kicks off for the U.S., many folks are starting to talk about La Niña—that mystical force that seems to bring tons of snow to some spots and a lack of flakes to others. Here’s the scoop on La Niña and how it might affect your winter.
   
La Niña means that water temperatures in a large area of the central Pacific Ocean (around the equator) are below normal. These below normal water temperatures influence global weather patterns, especially during the winter for the U.S.

Below normal water temperatures

Below normal water temperatures in the central Pacific Ocean give La Niña her fury. Image Courtesy of NOAA.

This strong influence on winter weather is important because it provides some confidence in the seasonal snow forecast over the next three to six months. Many people are skeptical of long-range weather forecasts; especially those that purport to predict amounts of snow or rain for the next half a year. That skepticism is generally warranted—except perhaps during a La Niña (or El Niño) winter.

In the absence of La Niña (or El Niño), forecasts for an entire winter are usually not very instructive. However, when La Niña (or El Niño) influences the weather patterns, meteorologists can often provide a more confident seasonal forecast by looking at snowfall from past La Niña seasons. In short, La Niña gives us a historical guide to forecasting the future.

La Nina weather patterns

Forecasters are projecting a return of La Niña this winter, but perhaps with less gusto than last season. Image Courtesy of NOAA.

Last season was a moderate to strong La Niña winter, and many times the winter following such a La Niña sees a second coming of “the little girl.” Indeed this expectation has proven true, and a weak to perhaps moderate La Niña is in store for this season as well.

But enough with science speak—how will La Niña affect your winter plans?

In general, more snow should fall on the northern half of the country. This includes Oregon, Washington, Idaho, Montana, Wyoming, the upper midwest, and also the far northern parts of New England. These areas did see tons of snow last season, with some places reporting 150 percent of average snowfall in the Pacific Northwest.

The in-between areas are less certain, such as California, Utah and Colorado. Last season, most of these areas also had much above average snowfall, but that’s more of a lucky outcome than a guarantee from La Niña.

In the southern locations such as Southern California, Arizona and New Mexico, La Niña often provides less snow than average. However, last season was an exception for southern California, where Mammoth saw over 175% of their seasonal average.

The take away from La Niña is this: the cards are in favor of much above average snowfall for northern areas of the U.S., though each winter storm that crosses the states can behave in its own way and bring lots of snow to areas not typically favored by La Niña. But regardless of global climate patterns, there is a 100 percent guaranteed forecast for the winter: It will snow and you will have fun.

Joel Gratz is the founder and meteorologist behind ColoradoPowderForecast.com.