Monday, October 3, 2011

La Nina Update

Monday, October 3, 2011
12:28 P.M.

I saw an article the La Nina episode we are currently seeing in the Seattle times today, so I thought I'd just give an update on the current La Nina situation. The La Nina has strengthened slightly, and although it won't become as strong as last year's, all indications point to a cooler and wetter winter for the Pacific Northwest.

Take a look at the general anomalies over the equatorial Pacific below.

Weekly SST anomalies from week centered around 9/28/11

Also, look at the diagram below of the anomalies in specific regions. As you can see, there is a clear downward trend in sea surface temperatures. The overall temperature varies from week to week as different weather conditions alter the temperature, but you can see the big picture. The tropical Pacific is colder than normal, and these anomalies are forecast to increase in the next couple months.

SST anomalies from four sites over the Pacific

Another interesting graphic shows the anomalies in temperature below the surface. It is shown below.

Mean and Anomalous Equatorial Pacific Temperatures

This graphic above is probably my favorite graphic, because it not only shows the ocean temperature anomalies at all depths, but it also gives you an idea of what the temperatures over there look like. Apart from super intense El Nino years, the Eastern Pacific is always colder because there is constant upwelling off the coast of Peru. In El Nino years, this upwelling is reduced or stopped, resulting in warmer water temperatures off of the Peruvian coast.

Andy Wappler, former meteorologist for Kiro TV, said that we should expect "colder, stormier weather than normal." I agree with the colder weather part, and we will see more rain than usual. I'm not so sure about the "stormier" part though. It depends how you define it, of course, but all of our major inland windstorms have struck during neutral years. During the La Nina year of 2007-2008, we saw one of the strongest storms ever to hit the Pacific Northwest, the December 1-3, 2007 "Great Coastal Gale." Many places in Western Washington saw record flooding, and the Chehalis reached record flood stage. The coast saw winds approaching 140 mph in spots. The Puget Sound area, however, did not see high winds. We may see a major windstorm this year, but just because it is a La Nina year doesn't mean you will see super strong storms. Generally, you will just see more regular storms, which, coupled with cooler than normal temperatures, produce gobs of snow in the mountains and slightly more snow in the lowlands. There is a chance that the lowlands could see a significant snow event. I'll keep you posted on that one.

As far as a weather forecast goes, the Tuesday storm that prompted the "Special Weather Statement" has continued to weaken in the models, and the "Special Weather Statement" has been discontinued. Expect unsettled weather from Monday to Wednesday, with calmer weather Thursday and Friday. It will be cooler than normal throughout the period.

Thanks for reading!

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