Every few years the equatorial Pacific Ocean warms, producing the phenomenon known as El Nino and causing a whole raft of environmental impacts around much of the world. The pattern was named by South American fishermen in the 1600's who noticed a change in fishing conditions around the Christmas season.
The main effect across the southwestern U.S. is typically increased rain and snow. But meteorologists want to know how much. To predict just how much of a change can be expected, they've been analyzing historical data.
Half a century of Pacific sea surface temperature records show that this year's warming trend is the third largest since records began.
With such a strong El Nino, there's a 50 to 60% chance that this winter will be wetter than average across northern Arizona. For high elevation areas that probably means more snowstorms than usual: for Flagstaff, a projected eight extra days with two or more inches of snow.
The size of storms is likely to be bigger, too. Strong El Nino years typically see five days with at least 8" of snowfall over the winter, instead of just 2 or 3.
But there's a catch. Each El Nino has its own "flavor", and there's around a 15% chance that it will impact another part of the country instead of the Southwest, leaving northern Arizona high and dry.
By mid-January we'll have a much better idea whether this year's El Nino will be a snowy Yuletide stocking filler - or not.