November Long Lead Outlooks Show Effects of La Nina
The Climate Prediction Center has issued it’s outlook for the month of November, and the updated forecasts show the predicted effects of the intensifying La Nina conditions. La Nina conditions occur when sea surface temperatures cool in the Pacific Ocean. The cooler ocean temperatures alter upper air patterns, and tend to cause warmer and dryer conditions in the Southeast, and wetter conditions in the Northwest.
In the discussion of the updated outlook, the Weather Service says that while earlier forecasts were based on computer models predicting La Nina conditions, this month, actual measurements confirm that a weak to moderate La Nina has started, increasing the confidence in the forecast.
For November, much of the country will be warmer than normal, especially over the Great Plains states. For much of the East coast, there is an equal chance of above normal or below normal temperatures. Part of the reasoning here is that the overall weather pattern is changing. Instead of the ridge of high pressure in the east and a trough in the west, the situation is expected to reverse, with upper level high pressure in the west and upper level low pressure in the east.
The precipitation forecast calls for above normal rainfall in the Pacific Northwest, and below normal rainfall for much of the Mid-Atlantic, Southern, and Southwestern states. This is pretty much what would be expected in a La Nina episode, and now that the chances of tropical weather diminish in November, we are less likely to see relief from a hurricane or tropical storm.
The La Nina conditions are also reflected in the longer range outlooks:
The precipitation outlook above for November-January also calls for less rainfall than normal, and if you take a look at the three month long lead forecasts for succeeding months, it looks like it might stay drier than normal until May, 2008.
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