Thursday, October 15, 2009

NOAA's 2009-2010 Winter Outlook: El Nino Rules

See here for other seasonal forecasts, including the current winter energy forecast.

In honor of Blog Action Day, here's a view of an effect which has a shorter time scale than climate, seasonal weather:

NOAA's Climate Prediction Center this morning issued its outlook for winter 2009-10 (December-January-February) in the U.S. It calls for a strengthening El Niño in the central and eastern tropical Pacific to dominate weather patterns for much of the country. The relatively warm Pacific water temperatures are expected to affect tropical rainfall distribution and in turn influence the strength and location of the storm track over North America.

The temperature forecast includes warmer than average temperatures over much of the West and central and northern Midwest. The best chance (over 40%) of warmer-than-average temperatures is from the northern Rockies eastward to Minnesota and as far south as Colorado and Nebraska. Temperatures are expected to be cooler than average from southern Texas northeastward to the Mid Atlantic area, including the Southeast. The Washington, DC region is on the borderline between the areas for over 33% chance (Maryland) and over 40% chance (most of Virginia) of cooler than average temperatures. The highest probability (over 40%) of cool temperatures is in the Southeast, from Virginia southward to Florida and westward along the Gulf Coast.

Precipitation is expected to be heavier than average along the central and southern West Coast eastward along the southern border and Gulf Coast through Florida. The wettest areas are likely to be most of California, central and southern Texas, and Florida. The driest areas relative to average are predicted to be the Pacific Northwest eastward across the northern Rockies and also from the northern Gulf States northeastward through the Ohio and Tennessee Valleys to the eastern Great Lakes.

Unlike the hype-casts promoted by certain commercial forecast services and media, the NOAA forecast recognizes the futility of predicting snowfall at seasonal time scales:
This seasonal outlook does not predict where and when snowstorms may hit or total seasonal snowfall accumulations. Snow forecasts are dependent upon winter storms, which are generally not predictable more than several days in advance.
Images (click to enlarge): U.S. winter 2009-2010 temperature and precipitation outlook and most recent Pacific sea-surface temperature (SST) departures from average, from Climate Prediction Center/NOAA

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Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.