March - May 2004

Latest Seasonal Assessment - A series of snowstorms eased drought in the Great Plains from late January into February, and the seasonal drought outlook suggests continued improvement into spring, with the best chances for relief extending across eastern portions of South Dakota, Nebraska, and Kansas into Minnesota and Wisconsin. Improvement is also slated for southern Oklahoma and northern Texas. More limited improvement is on tap for the western High Plains into Montana, Wyoming, western Colorado, and eastern Utah, as well as western Texas and much of New Mexico. Although the first half of the snow season has been disappointing for the drought areas in the Southwest, with the mid-February water content of the mountain snowpack less than two-thirds of normal over much of Arizona and New Mexico, the weather pattern has been changing, and a series of storms is forecast to bring prolific rain and snow to large portions of the West during the last half of February. The official precipitation outlook suggests the wet pattern could continue into March over parts of the Southwest. Drought improvement is also anticipated northward into eastern Colorado and across Nevada into Oregon and Idaho. Although some relief is expected across the West, this does not mean full drought recovery, as the region has a long way to go before water supplies are fully restored. As of February 1, four western states - Nevada, New Mexico, Oregon, and Utah - measured reservoir storage that was one-half or less of normal. And every western state reported below-normal levels except for California. As a result, it remains likely that some water shortages will persist into summer, especially in the Southwest.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for March-May, the Palmer Drought Index Probability Projections for May, various medium and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, and the soil moisture tools based on the GFS model and the Constucted Analogues for the season.

The drought forecast calls for more improvement this month over many areas due to both short and long-term considerations. Short term, the upper-level circulation pattern for the last 2 weeks of February is forecast to show a broad band of lower heights extending coast to coast across the southern half of the country. This leads to a series of Pacific low pressure areas entering the West Coast, tracking across the Southwest, and moving across the Plains. Abundant and widespread areas of rain or snow appear likely to accompany these storms. For the two weeks beginning on February 18, heaviest rain and snow totals should be extending from California, Nevada, and Arizona northeastward into the central Plains. Although the forecast going into next month is, as always, much less certain, there are some forecast tools that suggest wetness will continue over at least parts of the Southwest, as shown on CPC's official precipitation outlook for March. Green areas on the outlook map indicate those areas where the drought intensity levels depicted on the weekly U.S. Drought Monitor are likely to improve by one category or more as of the end of May. Hatched areas, where more limited improvement is expected, are shown where precipitation amounts over the seasonal forecast period should be lower and water shortages are most likely to persist.

In the Plains states, the 2-week forecast supports drought improvement in the central Plains, while climatology supports improvement over the longer term, with normal monthly rainfall climbing to 4 to 6 inches over large parts of the Plains in May. The hatched area in western Nebraska is based on the likelihood of water shortages continuing in this area. Both climatology and the Constructed Analogs from Soil Moisture (CAS) suggest more limited improvement in western South Dakota. The latter tool also suggests more limited improvement in western Colorado and eastern Utah.

Elsewhere, several forecast tools suggest dryness in Florida during the March-May season. This remains an area to watch, but the CAS soil moisture forecasts are now backing away from bringing significant dryness to Florida and the Southeast, and the official seasonal temperature outlook does not call for above-normal warmth, so no drought development is indicated at this time. Ample to excessive soil moisture levels argue against drought development this spring across most of the East.