Latest Seasonal Assessment -
The forecast continues to show persisting drought across the Southeast, with the odds favoring expansion into Florida and the Gulf Coast.
The ongoing La Niña is expected to bring abnormally mild and dry weather to the region this winter. Improvement remains on tap from Tennessee
and Kentucky into the mid-Atlantic and New England. Scattered drought areas in the Midwest should also see improvement. In the Southwest,
unusually heavy rains eased drought at the end of November and the first day of December. More storm systems during December will bring
additional relief to the Great Basin, California, and the Southwest, although there is a chance that drier weather will return by the end
of winter. Continued drought relief is expected in the interior Northwest and the northern Rockies, but little relief is expected from
the western Dakotas into western Nebraska. To the south, drought is forecast to develop in western and southern Texas, eastern New Mexico,
and northward into parts of Colorado, Oklahoma, and Kansas, although beneficial rains should ease drought along parts of the Texas-Oklahoma
border. Improvement will continue for the lingering drought in parts of Hawaii.
Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for December - February 2007/08, the four-month drought termination and amelioration probabilities, 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 moisture, the CFS seasonal precipitation forecasts, and La Niña composites of soil moisture.
Across the southeast, Gulf Coast and Florida, this forecast made little change to last month’s forecast. Drought persistence or development should be widespread with La Nina conditions typically bringing subnormal precipitation to the region during the forecast time period. Exceptional drought continues for parts of Alabama and Georgia, where year-to-date precipitation deficits in excess of 15 inches are common.
Farther inland across eastern parts of Kentucky and Tennessee, near or above normal precipitation typically occurs during La Nina winters, and medium-range and long-range forecast models remain consistent with this scenario. Also, soil moisture composites indicate an increased likelihood for improvement. Therefore, odds are for improvement for northern Tennessee into eastern Kentucky. However, some improvement is forecast for areas suffering from exceptional drought as complete drought elimination is not likely. Medium-range forecasts and recent trends continue to support improvement in the drought still affecting northern Virginia, Maryland, Delaware, and southern New England.
Across the Great Lakes and the Midwest, improvement for the small areas of moderate drought remains likely due to expected wetness either in the medium-range forecasts or in the monthly and seasonal forecasts. Improvement was scaled back in the western Dakotas and western Nebraska due largely to seasonal considerations, as drought relief is usually not seen during the winter due to frozen ground and relatively light precipitation totals.
In the West, La Nina favors above normal precipitation for the interior Pacific Northwest and northern Rockies, and the storm striking the Pacific Coast in early December brought rain and snow to the drought areas from the interior Northwest to the northern Rockies, and long-range forecasts indicate relief will continue.
Up to 5 inches of rain hit the drought area in Arizona, and over an inch even fell in the desert areas of Nevada and southern California during the storm that struck at the end of November and continued into the first day of December. With more heavy rain forecast for December 7-9, the drought forecast changed to show improvement southward into parts of Arizona, with more limited improvement forecast for central and southern California and southern Arizona. The forecast would be even more optimistic if it were not for most seasonal forecast models showing dryness this winter in the Southwest, and La Nina composites as well. The big question is whether or not conditions will return to dryness this winter, resulting in drought returning or intensifying. In this regard, the monthly CFS precipitation maps were considered. With these forecasts showing wetness for much of the Southwest through January, it seems that the December wetness may not be an isolated instance. However, dryness returns in February and continues through spring from California through Arizona and New Mexico. The map label has been modified to include the “near-term” wording to suggest that the wetter conditions may not persist throughout winter.
Finally, with Hawaii progressing into its wetter time of the year, La Nina composites favoring above-normal precipitation, and wet-looking short-term forecasts, improvement is forecast for those small drought-affected areas remaining across the island chain.