Thursday, October 21, 2010

NOAA 2010-2011 Winter Outlook: Strong La Niña Bringing More Extremes;
Above Average Temperatures Over Much of Country

The winter weather outlook (December 2010-February 2011) released this morning by NOAA's Climate Prediction Center is dominated by the effects of a developing strong La Niña. Temperatures are forecast to be above the long-term average from the Ohio Valley through most of the Southeast and westward to the Rockies. The warmest area relative to average is predicted from southern New Mexico eastward through most of Texas and Louisiana.

The only areas expected to be cooler than average are along the immediate Pacific Coast and eastward along the Canadian border to northern Minnesota. There are equal chances of above or below normal temperatures in the interior of the West and across the Great Lakes, Mid Atlantic, Northeast, and southern Florida.

Precipitation is predicted to be above average in the eastern Great Lakes, Ohio and mid-Mississippi Valleys, and from the Pacific Northwest and northern California eastward across the northern Rockies. The wettest areas relative to average are likely to be the Pacific Northwest, northern Rockies, and lower Ohio Valley.

Drier-than-average conditions are forecast along the southern tier of states from the Southwest eastward across the Gulf Coast to the Southeast, with the driest conditions through central and northern Florida. The National Weather Service chart of West Palm Beach precipitation, to the right, shows the drastic reduction of dry season rainfall during past moderate to strong La Niña patterns. The red bars represent the precipitation deficit, and the green bar represents the climatological precipitation total.

Equal chances of above or below average precipitation are expected from central and southern California eastward across the central Rockies and much of the Great Plains, as well as from the central Appalachians northeastward through the Mid Atlantic and Northeast.

The seasonal drought outlook for the next 3 months (November-January) calls for persistence or intensification of drought conditions in the Southeast, but with improvement of conditions in more northern areas, particularly the lower Ohio Valley and Mid Atlantic.

La Niña is defined by cooler than average sea surface temperatures in the equatorial Pacific Ocean. The current La Niña continued to develop during September, and the latest outlook calls for it to strengthen into the winter and continue through at least the spring.

For the DMV (DC, Maryland, and Virginia), there are equal chances of above or below temperature and precipitation. Average temperature, precipitation, and snowfall for Washington in the winter are:
        Temperature Precipitation Snowfall
December 39.5 3.05" 1.5"
January 34.9 3.21" 6.2"
February 38.1 2.63" 5.2"
Winter 37.5 8.89" 15.2" (Nov-Mar)
For some caveats on the forecast, see The Weather Channel's analysis: NOAA Issues Winter Outlook

Images (click to enlarge), from Climate Prediction Center/NOAA and National Weather Service:
  • U.S. winter 2010-11 temperature outlook
  • U.S. winter 2010-11 precipitation outlook
  • Historical West Palm Beach La Niña precipitation amounts
  • November-January U.S. drought outlook
  • Typical North American La Niña jet stream and weather patterns
  • Weekly equatorial Pacific sea surface temperatures, Oct. 2009-Sept. 2010

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Seasonal Outlook

Latest seasonal forecast: Click here.

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