March - May 2008

Latest Seasonal Assessment - The Southeastern drought region should continue to see improvement, with the best odds for relief extending across the northern part of the drought area as well as along the coast. One storm system brought widespread relief during March 3-4, while another storm system will bring another shot of rain on March 7-9. More limited improvement is expected over the longer run in the southern parts of the drought region due to seasonal forecasts of drier weather by April. Drought will improve on the northwestern peninsula of Florida, but persist and expand across southern Florida. Farther west, drought is forecast to persist over central Texas and in the western Oklahoma Panhandle region, with the odds still favoring expansion into west Texas and eastern New Mexico. Forecasts for drier weather have led to the Outlook showing persisting drought over southern California and southern Nevada, although deep mountain snow pack will boost water supplies this spring. To the north, improvement is anticipated over the northern Great Basin, while more limited improvement is forecast for the northern High Plains. Little change is expected over the far western Dakotas, but the odds for improvement increase to the east into Minnesota.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for March – May 2008, the for March, 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 and soil moisture forecasts, and La Niña.

The changes from the February 21 drought outlook are generally minor. Increased improvement is shown for the Southeast drought region due largely to short-term rainfall forecasts, with 1-2 inches of rain likely from Virginia southward into the Carolinas and Georgia on March 7-9. The area of improvement now extends along the coast of Virginia and the Carolinas. Besides the near-term relief, the latest GFS model runs indicate additional storm systems around the middle of March. In contrast, long-range forecasts and models continue to point to the possibility of drier weather returning to the region during April and May. Splitting the differences between the long-range and short-range forecasts results in more limited improvement from central Alabama into south-central North Carolina. This is the area more likely to see dry weather later this season if the long-range forecasts pan out. La Niña is forecast to continue through spring, consistent with some drier weather returning to the Southeast. However, it should be noted that the long range models and La Niña composites have been too dry for much of the Southeast in recent months, so confidence is relatively low that the dry pattern will return. Recent wet conditions and short-term forecasts of more rain removed the area of drought development from northern Florida and led to the forecast for improvement for the northwest peninsula. Continuing to show development in southern Florida is consistent with the ongoing La Niña and CFS model soil moisture forecasts.

Elsewhere, east Texas has seen some recent rain, and short-range forecasts point to more moisture during the early part of the forecast period. As a result, the slim area of development shown last month east of the ongoing drought region has been removed. The drought is still expected to persist in central Texas and expand into eastern and southern New Mexico, as seasonal forecasts are consistent in showing dryness in this region. The eastern part of the drought region may see some good rains during March, but longer-range dryness should offset short-term relief. The development area was pulled back from southwest Nebraska and northwest Kansas due to lack of dryness in the medium range and CPC updated monthly forecasts. The monthly forecast shows the best odds for below-normal rainfall extending from southern and western Texas into southern California. The consistency of short, medium, and long-range forecasts showing below-normal precipitation led to expansion northward of the persisting drought area in interior southern California. However, well above-normal mountain snow pack will lead to water supply boosts this spring. Relief is still expected in the northern Great Basin. The CFS soil moisture model shows improvement from northern Utah into Idaho and Oregon by the end of May, and the updated monthly forecast shows above-normal precipitation from western Montana westward. The odds for improvement diminish to the east into the Northern Plains. The persisting area in the western Dakotas grew smaller in this forecast due to more favorable medium-range forecasts. From the eastern Dakotas into Minnesota, medium-range forecasts, March, April, and May long-range model forecasts, and La Niña composites are consistent in showing a tendency toward above-normal precipitation this season, so improvement is depicted for the small areas of drought in southeastern North Dakota and western Minnesota.