Friday, October 18, 2013

El Niño - La Niña Update - Forecast, October 2013

El Niño - La Niña Update - Forecast, October 2013.

Our globe is approximately 70% covered by ocean water. It has been known for many decades that the temperatures and temperature anomalies in the ocean can have a significant influence on our weather patterns in the U.S.  The Pacific Ocean has the most influence on the climate of the U.S. so therefore we monitor continuously the temperature anomalies in that ocean.  There is a listing of links at our weather links page that will provide some background information on El Niño (warm) and La Niña (cold) events and how the Pacific Ocean temperatures during these events impact our weather in the U.S.
The graph below shows forecasts made by dynamical and statistical models for Sea Surface Temperatures (SSTs) for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Thirdly, forecasts made at some times of the year generally have higher skill than forecasts made at other times of the year--namely, they are better when made between June and December than when they are made between February and May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario. The thick yellow line shows the average of the models. Our Northern Hemisphere Winter is the time period DJF (December though February). Values below -0.5 are La Niña conditions and values greater than +0.5 are El Niño conditions.  One of the models puts us into a strong La Niña for the upcoming winter season and several forecast models move us close to El Niño conditions.  Many of the forecast models however indicate neutral conditions and the average of all the models (yellow line) has the index close to 0.

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