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Climate Prediction Center


December 2010 - February 2011


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Latest Seasonal Assessment - Drought continued to slowly expand and locally intensify in a broad area across the southern and southeastern states, the lower Mississippi Valley, and the lower Ohio Valley northward through Indiana and southern Michigan. Based on the Seasonal Outlook for December 2010 - January 2011, which relies primarily on climate anomalies typically observed during La Niña episodes, drought persistence and broad expansion is expected from central and southern Texas eastward along and near the Gulf Coast through the southern Atlantic Seaboard. Chances for drought improvement increase away from the coastal plains, with some improvement forecast across the upper South, and broad-scale improvement expected from southern portions of the middle Mississippi Valley through the lower Ohio Valley and points north. As in areas farther east, the drought region in northeastern Arizona is forecast to persist and expand, covering large sections of the southern Four Corners region by the end of February. The recently-expanded drought across the central High Plains is also expected to persist through this period, which is their driest time of year climatologically. Farther west, limited drought improvement is expected across central Nevada, but more substantial improvement seems likely in western Wyoming and across the drought region in northeast California, southern Oregon, and adjacent areas. In Hawaii, the seasonal increase in rainfall and a modest tilt of the odds toward a wetter than normal winter season should bring limited improvement to the areas affected by drought, but the large, long-term precipitation shortages recorded in these areas will likely preclude any widespread, substantial improvement by the end of the period.

Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the official CPC precipitation outlook for December 2010 and the long lead forecast for December 2010 - February 2011, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the soil moisture tools based on the GFS model and the Constructed Analogue on Soil (CAS) moisture, the Climate Forecast System (CFS) seasonal precipitation forecasts, La Niña composites for the December - February season, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

In the two weeks since the last Drought Outlook was issued on November 4, severe drought was finally eradicated in the eastern West Virginia panhandle. However, two areas of moderate drought persisted in eastern parts of the state on November 18. Little precipitation is expected through November 22, but the 6-10 day and 8-14 day outlooks covering the period November 23 - December 1 both show odds favoring above-normal precipitation. For the ensuing three months, neither dryness nor wetness is favored in relevant La Niña composites and the official December 2010 - February 2011 Seasonal Outlook. As a result, some improvement is anticipated in these regions. However, the non-committal seasonal forecast and the fact that precipitation deficits, while relatively modest, date back 6 to 12 months reduces the chances that drought will be eliminated completely by the end of February 2011.
Forecast confidence is low.

Large areas of either drought or abnormal dryness approaching drought intensity cover a large portion of the southern and southeastern United States as of November 18, with regions of severe drought and patches of extreme drought near the Mississippi River, portions of Alabama, southern Georgia, and much of northern and eastern Florida. Looking at the expansive area from central and southern Texas eastward and northeastward through central and southern Arkansas, Louisiana, Mississippi, most of Alabama and Georgia, Florida, and the Carolinas, the outlook generally improves as one moves away from the Gulf Coast and south Atlantic Seaboard, as indicated by a relatively consistent signal in moderate to strong La Niña composites as well as the December 2010 - February 2011 Seasonal Outlook. In shorter time frames, less than 0.5 inch of precipitation is expected during the next 5 days regionwide, and for the remainder of November, forecasts look similar to the Seasonal Outlook, with near- to below- normal precipitation favored in Florida and near the Gulf and south Atlantic Coasts while heavier precipitation is more likely farther inland. Above-normal precipitation is favored near the end of the month as far south as central Louisiana, southern non-coastal Mississippi, and south-central sections of Alabama, Georgia, and South Carolina. However, the relatively high confidence and agreement of the various tools for the December 2010 - February 2011 period implies that any short-term wetness slightly removed from the coasts will not significantly influence conditions by the end of February 2011. As a result, the Drought Outlook calls for drought to persist or expand to cover much of central and southern Texas, central and southern Louisiana, southern and eastern Mississippi, central and southern sections of Alabama and Georgia, all of Florida, and all but the northern and western tiers of the Carolinas. As of November 18, dryness and drought is just as extensive farther north through northern Louisiana, central and southern Arkansas, central and northern Mississippi, northern sections of Alabama and Georgia, southeastern Tennessee, and the northern and western tiers of the Carolinas. However, the odds for below-normal December 2010 - February 2011 precipitation decline to the point where no particular tilt of the odds toward wetness or dryness is evident. Therefore, some improvement is forecast for these areas, with no anticipated drought expansion.
Forecast confidence in the south-central and southeastern states is high except in areas where development is forecast but antecedent conditions are not abnormally dry, specifically the eastern Carolinas, southernmost Florida, most of southern Louisiana, and southeastern Texas, where confidence is moderate.

As in areas farther south, a broad area of drought extends from northeastern Arkansas and western Tennessee northward along the middle Mississippi and lower Ohio River Valleys, then through Indiana and southern Michigan. Since the last Drought Outlook issued November 4, drought has modestly expanded and intensified throughout the region, but that trend is not expected to continue through the winter months. Light precipitation at best is expected regionwide during November 18 - 22, but thereafter all tools indicate enhanced odds for above-normal precipitation, including the 6- to 10-day and 8- to 14-day forecasts, composites of past moderate to strong La Niña years, and the official December 2010 - February 2011 Seasonal Outlook. As a result, improvement is forecast throughout the region by the end of the period.
Forecast confidence is high throughout this area which extends from southern sections of the middle Mississippi Valley northeastward through the lower and middle Ohio Valley and the south-central Great Lakes region.

A small area of moderate drought persists in northeastern Minnesota. The odds favor above-normal precipitation until the end of November, with no discernable tilt of the odds toward dryness or wetness indicated for December 2010 - February 2011. Considering the short-term forecast, an ongoing trend of increasing precipitation, and the fact that winter is the ideal time of year for moisture replenishment in the area (frequent and extended periods of sub-freezing temperatures that allow for little snowmelt and no evapotranspiration), drought improvement is forecast.
Forecast confidence for the upper Midwest is high.

Moderate drought has expanded to cover the Nebraska panhandle, most of the eastern half of Colorado, and west-central Kansas since the last Drought Outlook issued November 4. Light to perhaps moderate precipitation, at least somewhat above normal, is expected into late November, but odds favor dryness during the end of the month. While the Seasonal Outlook is non-committal regarding precipitation during December 2010 - February 2011, this is a very dry time of the year climatologically, so it is unlikely, though not impossible, that enough precipitation will fall by the end of February 2011 to substantially ameliorate the 1.5 to 3.0 inch deficits that have accumulated since mid-August 2010. Therefore, the drought is expected to persist through this period.
Forecast confidence for the central High Plains is moderate.

As of November 18, drought covered part of northeastern Arizona, and a much larger area of abnormally dry conditions extended through much of northern and western Arizona, northern and western New Mexico, and adjacent sections of Nevada and Colorado. Light precipitation is forecast during November 18 - 22 across much of these areas, with totals locally exceeding 0.5 inch in the central Arizona highlands. Thereafter, below-normal precipitation is favored for late November and in the December 2010 - February 2011 Seasonal Outlook, consistent with composites of past moderate to strong La Niña years. As a result, drought is forecast to persist in northeastern Arizona and expand to cover the rest of the areas above now assessed as abnormally dry. Additionally, drought is expected to develop in central Arizona, where winter is a slightly wetter time of year climatologically than most other 3-month periods, and where winter snowpack in the higher elevations could be substantially below normal by the end of the period.
Forecast Confidence for southern sections of the Four Corners states is high.

There are only a few scattered patches of drought lingering in the remainder of the western United States, although where there is drought, it has persisted for at least 9 months, and for more than a year in central Nevada and across southern Oregon, northeastern California, and adjacent areas. Above-normal precipitation is likely in central Nevada into late November, but the Seasonal Outlook shows no tilt of the odds toward either dryness or wetness during the winter months. Based on near-term wetness but uncertainty thereafter, some improvement seems the forecast of least regret, without much confidence, in central Nevada. Farther north, generally 0.5 to 1.0 inch of precipitation is expected to fall on the drought areas in Wyoming and across northeastern California, southern Oregon, and adjacent area. The odds favor above-normal precipitation in these areas during the ensuing 5 days, and the Seasonal Outlook favors above-normal precipitation through these same areas during December 2010 - February 2011. Therefore, improvement is expected.
Forecast confidence is low in central Nevada, and moderate to high in western Wyoming, and for the area in and adjacent to northeastern California and south-central Oregon.

Drought expanded across much of Hawaii due to the El Niño event from mid-2009 until early 2010, and has persisted or intensified since. Rainfall normally increases during the winter, and Hawaii receives at least somewhat enhanced precipitation more often than not during La Niña years December - February, with better likelihoods for above-normal precipitation in the ensuing months. Given the rather modest tilt of the odds toward above-normal December 2010 - February 2011 precipitation, and the protracted nature of the current drought, which is classified as extreme to exceptional in some areas, only some improvement is expected by the end of the period.
Forecast confidence for Hawaii is moderate.

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Page Author: Climate Prediction Center Internet Team
Page last modified November 18, 2010
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