Western US weather expert
Early Winter Prediction: La Nina Making a Big Comeback
9/19/2011, 6:49:13 AM
It looks like it will be another winter that brings a moderate La Nina pattern. From the middle of spring into early summer, conditions went into the El Nino territory for a time, but then things quickly reversed and have been strong trending to La Nina since.
Average sea surface temperatures are now below normal in much of the Eastern Pacific, especially from off the California and Baja coasts on southwest and west of South America.
Both of the above have pretty much put the lid on the hurricane season in the Eastern Pacific. The last named storm, Greg, dissipated almost a month ago on Aug. 20.
These charts show that over the last 30 days, sea surface temperatures have decreased in the Eastern Pacific region.
Models continue this trend throughout the fall and winter seasons. First, here are all the models.
And here is the ensemble mean.
So what do all these charts mean? To me, it seems likely that La Nina is here to stay through the coming winter, and it will more than likely become stronger with time. It could become as strong as last winter's La Nina, certainly nearly as strong. This should generally bring typical La Nina winter weather, being wetter than normal from northern California into the Northwest and across the northern to the central Rockies and Great Basin. It should also mean drier-than-normal weather from the Southwest into the South Central states. This, of course, is very bad news from Texas to New Mexico, which have been suffering through some of the driest weather in decades. It also is not good news for Arizona. As for south-central and Southern California, La Nina usually means a drier-than-normal rainfall season in this area as well. As we all know, that is not always the case; take last year. I am not as confident about this area again this winter having below-normal precipitation. The summer pattern showed storms coming farther south than normal before lifting northeast, exactly what happened last winter. If we continue to have an active storm pattern in the Eastern Pacific west of California, then we could have a repeat of an untypical La Nina winter in the southern third of California. The chances of it being as wet as last year are statistically quite low. But even a normally wet winter would be unusual (and welcomed).
I will continue to be watching the trends over the next month or so and keep you informed about any changes.
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