March - May 2008

Latest Seasonal Assessment - The northern part of the Southeastern drought region should continue to see improvement, while the odds for drought relief by the end of May diminish farther south, resulting in more limited improvement from central Alabama into the Carolinas and southeastern Virginia. A continuation of a stormy pattern for at least the latter part of February will result in beneficial moisture for most of the drought region. In contrast, the odds favor above-normal temperatures and below-normal rainfall during March-May across the Southeast, so there is a good chance that conditions will deteriorate following the near-term improvement. Even where improvement is anticipated, many reservoirs and wells will remain low due to lingering impacts from the extreme rainfall deficits incurred last year. Elsewhere, developing drought remains likely across the southern Plains from central Texas into eastern and southern New Mexico and northward into southwestern Nebraska. Consistent with the persisting La Niña episode, medium and long-range forecasts indicate below-normal rainfall for this region. Year-to-date rainfall through February 19 was less than 25 percent of normal in parts of southeastern New Mexico and southern and western Texas. In the Northern Plains, drought is expected to persist from southwestern North Dakota into western Nebraska, with some improvement to the north and west, and more substantial improvement over the Great Basin. Lingering drought may persist in southern California and southwestern Arizona due to a dry pattern forecast for March-May.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for March – May 2008, the monthly precipitation forecast 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.

Widespread rains during the first 2 weeks of the forecast period will offer beneficial moisture to the Southeast drought region, and this comes on top of good rains earlier in February. The official 5-day forecast for February 20-25 shows 1 to 2 inches of rain from Alabama into North Carolina, and the 6-10 day and week 2 forecasts indicate normal to above-normal precipitation for the region. In contrast, the longer range forecasts remain less optimistic, with the latest official March and March-May outlooks showing a tilt of the odds toward below-normal rainfall for states south and east of Tennessee, with the strongest odds for dryness in the 3-month outlook extending across the southern two-thirds of Alabama, Georgia, and South Carolina, and into much of Florida. The contrast between the wet start to the forecast period and the drier conditions expected later on makes for a challenging depiction on the Drought Outlook map once again, and an area of some improvement was used to denote the variable conditions expected during the forecast period from central Alabama into southeastern Virginia. This is more optimistic than the prior drought forecast, which indicated persisting drought for part of the region. This is because of the widespread rains anticipated during the first days of the valid period. The Southeastern drought will likely continue in some shape or form over the next several months at a minimum, given 12-month rainfall deficits still exceed 20 inches in the driest areas and some reservoirs remain far below capacity. Lake Lanier, serving the Atlanta area, rose by 1 foot from February 1 to 19, and by 2 feet since it bottomed out on December 26, but is still some 14 feet below average and 17 feet below capacity.

The development area across the southern Plains has been peeled back slightly on the eastern edge in Texas and Oklahoma because of recent rains but the area has also expanded slightly northward into southwestern Nebraska. The expansion is supported by a number of tools, including the official 3-month precipitation forecast and the CFS (Climate Forecast System) modeled soil moisture change to May. The confidence for worsening conditions from western Texas into southern and eastern New Mexico is relatively high due to the agreement among numerous forecast tools. Farther north, the CFS soil moisture forecasts, Palmer Drought Index probabilities, La Niña precipitation composites, and CAS soil moisture forecasts all suggest little improvement to be expected from southwestern North Dakota into western Nebraska.

There is little change to the forecast for the West, with a slightly more optimistic depiction for the northern part of the southern California drought area due to near-term precipitation forecasts. The spring and summer stream flow forecasts as of February 1 prepared by the USDA Natural Resources Conservation Service indicated near to above-normal flows for most of the West, with especially high flows in Arizona, western and northern New Mexico, and much of Colorado and Utah.