This year’s winter forecast is going to look a lot like last year’s. That’s because last winter was a La Nina winter and this winter almost certainly will be one, (or already is depending on your point of view). And how did my forecast for last winter turn out? Here’s that story. A twist to this winter is the speculation by some that there might be some significance to a 2nd consecutive, or double-dip, La Nina.
But first, what is a La Nina, how does it affect our weather, and can it really allow one to make a five month or longer forecast? Very briefly, a La Nina is one phase of a oscillating weather pattern in the equatorial Pacific involving air pressure patterns, winds and sea water temperatures. That a weather pattern roughly 4,000 miles (6,000 km) away can affect Alaska’s weather shows the large, interconnected nature of Pacific weather and climate systems and how important ocean temperatures are to them. The tropical part of this system has been studied for decades and is termed the El Nino/Southern Oscillation, or ENSO for short. La Nina is the cool phase of this tropical system, El Nino the warm phase. It oscillates between the two famous kids on a more or less yearly basis, typically with a lull during the northern hemisphere summer and an intensification in fall and through the winter. Many years the phenomenon is weak or noncommittal…a neutral phase. Here’s a intuitive graph from the NOAA’s Earth Systems Research Lab:
For more information on the the ENSO see the links at the end of the post. (more…)