La Niña conditions strengthen across the east-central equatorial Pacific Ocean, but the models favor a weak-to-moderate strength La Niña during the Northern Hemisphere winter


Here’s the latest discussion from the Climate Prediction Center. Click through for the cool graphics. Here’s an excerpt:

A majority of the models now predict La Niña to continue through the Northern Hemisphere winter (Fig. 6) and then gradually weaken after peaking during the November – January period. The models are roughly split between those that predict La Niña to remain weak (3-month average in the Nino-3.4 region less than -0.9°C) and those that predict a stronger episode. Over the last half-century, La Niña events that were preceded by ENSO-neutral conditions during the Northern Hemisphere summer (May-August) were less likely to attain strong amplitude (less than –1.5°C) the following winter. This observation, in combination with the model forecasts, favors a weak-to-moderate strength La Niña during the Northern Hemisphere winter.

During November 2011-January 2012, there is an increased chance of above-average temperatures across the south-central U.S. with the odds favoring below-average temperatures over the north-central U.S. Also, above-average precipitation is favored across the northern tier of states, excluding New England, and drier-than-average conditions are more probable across the southern tier of the U.S. (see 3-month seasonal outlook released on 20 October 2011).

Meanwhile it’s was warmer than normal in October across most of the U.S., according to Bob Berwyn writing for the Summit County Citizens Voice. From the article:

Eighteen states reported monthly temperatures readings above their long-term averages, while 11 states reported readings below the monthly average. In the Pacific Northwest , in the central and southern plains, and parts of the Midwest reported near average temperatures for October. Most of the states with below average readings were in the Southeast, which was the coolest region for the month, according to the monthly report from the National Climatic Data Center.

For the August-October period, readings across the U.S. were well above the historic average, ranking as the 10th warmest such period on record, especially across the West, where 10 states reported near-record readings…

As of Nov. 1, about 9 percent of the country was categorized as being in exceptional drought, with some improvement across the southern plains, which recorded near-normal precipitation for the month.

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