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Climate Prediction Center

 
 
 

December 2008 - February 2009

 

Latest Seasonal Assessment - Across the United States, significant drought relief looks to be the exception rather than the rule for the next few months. In the East, below-normal precipitation is expected through February 2009 in the south Atlantic states, thus drought is expected to persist in the Carolinas, Georgia, and northeast Alabama. Precipitation is expected to be more generous from the lower Appalachians through the central Ohio Valley, where some limited improvement is anticipated. Farther south, conditions are already somewhat dry in part of Florida, and drier than normal conditions are favored over the next few months. As a result, drought is expected to develop over central and northwestern sections of Peninsular Florida. Moving westward, drought should persist and expand slightly southward across central Texas, and persist through the western Great Lakes region as well, except in areas that typically receive substantial lake-effect snowfall. Drought should improve in south-central Oklahoma while more limited improvement is anticipated for the small areas of drought in the High Plains. Farther west, drought should persist in southwest Wyoming and part of adjacent Idaho, but at least limited improvement is expected through other areas west of the Rockies and outside the desert Southwest. Substantial improvement is expected in northern California, but it should be noted that complete alleviation of the moisture deficits that have accumulated over the last 2 years is unlikely. For central and southwestern California, central and north Nevada, and adjacent parts of Oregon, Idaho, and Utah, limited improvement is anticipated since winter is a relatively wet time of year and typically a period of hydrologic recharge and increasing mountain snowpack. In the desert Southwest, drought is expected to persist, and by February to expand into much of the western half of Arizona. It should be noted, however, that some indicators point toward a significant storm system moving through the region in late November, and should this or some subsequent system drop heavy precipitation on the region as it moves through, the drought situation could change markedly in a relatively short period of time. The region is among the most climatologically arid in the United States, and just a few inches of precipitation would be a significant proportion of the annual normal. Finally, drought conditions should improve throughout Hawaii.

 
Discussion for the Seasonal Drought Outlook

Tools used in the Drought Outlook included the official precipitation outlook for December-February, 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, and climatology.

The Drought Outlook calls for limited improvement over areas from Virginia and Tennessee northwestward into the central Ohio Valley; persistence across the Carolinas, Georgia, and northeast Alabama; and development in part of Peninsular Florida. Light to moderate precipitation is expected through late November in the areas forecast to experience some improvement, and the official CPC December-February precipitation outlook indicates equal chances for above-, near-, or below-normal precipitation across this region. In areas farther south and east, including the development area in Florida, short- to medium-range forecasts favor below-normal precipitation through November, as does the official December-February outlook. However, despite the generally pessimistic outlooks, winter is a season of reduced water demand, relatively low water loss to evaporation and plant or crop usage, and longer-duration precipitation events of light to moderate intensity, all of which favor hydrologic and soil moisture recharge. Significant improvement wonít occur if the precipitation outlooks are correct, but marked deterioration is also unlikely because of the time of year. For these reasons, the area highlighted for development was a relatively small portion of the area expected to be drier than normal through meteorological winter. Across central and northwestern peninsular Florida, soil moisture deficits are already in place with the past several months having been somewhat dry, and winter weather is typically more mild than in areas farther north, which implies increased evaporative water loss and plant demand.
Confidence for the Southeast: High

In the Great Lakes region, most precipitation tools donít particularly favor dryness or wetness over the next 3.5 months, although substantial lake-effect snowfall is expected into early Thanksgiving week in the Upper Peninsula of Michigan, and the odds slightly favor a wetter than normal December throughout the region, according to the official CPC monthly precipitation outlook. Still, indications are that surface moisture conditions should improve little during the period, so drought persistence is forecast for most of the region, with some improvement expected in the Upper Peninsula of Michigan where lake-effect snowfall is typically robust. Our confidence is eroded a bit by the lack of any significant precipitation signal for the period.
Confidence for the Great Lakes region: Moderate

In central Texas, drought is expected to persist, and expand somewhat to the south. Near- or below-normal precipitation is forecast through the rest of November, and both the official December monthly and December-February seasonal forecasts favor drier than normal weather. In addition, this is a relatively dry time of the year for the region, especially in the southern and western reaches.
Confidence for central Texas: High in western areas; moderate farther east

In southern Oklahoma, the official forecast for December-February favors enhanced precipitation following a relatively dry end to November. With no reason climatological or otherwise to alter the precipitation forecast for the purposes of the Drought Outlook, confidence mirrors that of the precipitation outlook.
Confidence for southern Oklahoma: Moderate

For the drought areas in the High Plains, one covering southeastern Colorado and northeastern New Mexico, and the other encompassing southwestern North Dakota and adjacent Montana, some improvement is anticipated. In the southernmost area, the official December-February outlook favors above-normal precipitation following a dry end to November. In the northern area, there is no precipitation signal for the winter season, and only light precipitation at best is expected through the end of November; however, winter is very cold in this area, so what falls is typically snow which can build up over the course of the winter and provide a soil moisture boost as it melts during the spring. In both drought areas, these considerations are tempered by the fact that precipitation totals are quite low compared to other times of the year.
Confidence for the High Plains: High

Farther west, in the sprawling drought area extending from California and southern Oregon eastward through the Intermountain West and into the central Rockies, expected changes to the current drought situation vary with location. The December-February outlook doesnít favor dryness or wetness anywhere in the existing drought area, but does tilt dry in part of Arizona that has been drier than normal for at least a few months. As a result, drought is expected to expand into this area by the end of February. As for the areas already experiencing full-fledged drought, improvement is anticipated in northern California, where December is expected to be wetter than normal and climatology indicates that normal precipitation is quite robust this time of year. For central and southwestern California, the Great Basin and adjacent areas, and southern Idaho, some improvement is expected. This is a relatively wet and cold time of year, especially in the higher elevations where building mountain snowpack, a primary source of water for the region, provides hydrologic recharge. With no indication as to how the season might progress relative to normal, climatology dictates a forecast for some improvement. Farther east, winter is actually one of the drier times of year in southwestern Wyoming, and again with nothing favoring either dryness or wetness for the next few months, climatological considerations imply persisting drought. The forecast for the desert Southwest is a difficult one. Drought is forecast to persist with some eastward expansion into Arizona, based essentially on the December-February forecast and the fact that, though the season is relatively wet in some areas, this is one of the driest regions in the country climatologically, and dryness has been entrenched in the area for some time. This points toward persistence as the most prudent forecast, but also introduces substantial uncertainty should a significant storm move through the region, which seems possible during late November. If this system or any subsequent system drops significant precipitation on the region, it could result in marked changes to the drought situation, since only a few inches of precipitation would be a substantial proportion of the normal annual total. Other parts of the West, where normal precipitation is more abundant, are not so sensitive to individual storm systems.
Confidence for the West: Low in the desert Southwest; moderate elsewhere

For the Hawaiian Islands, with the climatologically wet time of year approaching and short-term forecasts indicating that heavy rain and flash flooding are possible throughout the island chain, drought improvement is forecast.
Confidence for Hawaii: High

 

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Page last modified: November 20, 2008
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