williwaw.com

After a particularly nasty winter, Alaskans usually hope for a nice summer to erase the memories. Actually, a lot of Alaskan’s do that after every winter.  Well, we are just finishing up (or still waiting for the end of, depending on what part of Alaska you live in)  a very tough winter in most parts of Alaska, so hope runs high for the summer. Will it soothe or disappoint the weather weary?

The truthful answer? I don’t know. Seasonal forecasts for the warm season have little skill in Alaska. Worse than winter forecasts, which are far from reliable.

There are two points pertinent to this issue:

1. Temperatures vary much less in summer than in winter. While that might make it easier by reducing the potential forecast error,  in reality the forecast needs to show skill within the context of that variability. This is the technical explanation. From a human standpoint these smaller temperature variations seem to be relatively more important in summer, perhaps because there is more outside activity. There is about as much grumbling about a 3 degree colder than normal summer month as there is about a 6 degree colder than normal winter month.
2. Correlations of summer weather in Alaska with climate systems such as the El Nino/La Nina are either too weak or as yet too poorly understood to be a very useful predictor of a particular summer. Frankly most people have been trying to figure the links with winter weather, probably because winter weather is seen as more important (dangerous, costly, etc.) and I suppose that is right to an extent.

So I’m not putting much confidence in my prediction, and asking you not to as well. This is more of a theory to be played out over the next 3 months than something to make decisions on. (more…)

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…)