February - April 2004

Latest Seasonal Assessment - The season is off to a good start in most of the West, with mountain snow pack generally above normal across the Rockies and Intermountain region. Spring and summer streamflow forecasts indicate near to slightly below-normal conditions over the West except for the arid Southwest, where the prospects are dimmer. The winter snow season has a long way to go, and conditions could easily change between now and spring, but the seasonal drought outlook indicates that overall drought improvement is expected from the interior Northwest into western parts of Wyoming and Montana and southward into Utah and northern Nevada. In contrast, the season has been slow to start in Arizona and New Mexico, and precipitation prospects into April are generally lower, with the latest official outlook for February through April indicating a tendency for below normal precipitation over much of the Southwest. As a result, drought is expected to persist from Arizona into New Mexico. Abundant tropical moisture streaming into southern and eastern New Mexico, as well as Texas and Oklahoma, during January 14-17 will provide at least a temporary boost to moisture levels. In the central and northern Plains, periodic storms will offer some improvement to drought-afflicted areas, but significant improvement is not forecast at this time. Drought should largely persist from northwestern Kansas into western Nebraska.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for February-April, the Palmer Drought Index Probability Projections for April, 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 continues to call for improvement in the Pacific Northwest consistent with recent trends and the January 1 spring and summer streamflow forecasts. The forecast is based on both the short and long-term precipitation outlooks, the Constructed Analogue Soil (CAS) model, and the prospects for impact improvement based on the streamflow forecasts. The outlook for improvement is not as great in the hatched areas on the map in the West, relative to the green areas, generally due to lower streamflow forecasts, weaker trends, and lower soil moisture and precipitation forecasts from the CAS model. Prospects for improvement are lowest in the Southwest due to current low snow pack as well as a tendency for below-normal precipitation in the week 2 forecast and the February-April precipitation forecast. The hatched area in New Mexico and adjacent Texas is largely based on the rainfall event expected during January 14-17, which was getting underway as this forecast was being prepared. Forecast rainfall amounts exceeding 1 inch in southeastern New Mexico and across Texas will offer important short-term relief, but much more moisture will be needed to have a major impact on the ongoing drought in New Mexico and western Texas. Portions of southeastern New Mexico recorded less than one- third of their normal precipitation during 2003, so a number of rainfall events will be needed to erase the long-term deficits. Expected rainfall totals during January 14-17 could amount to as much as one-third of the total rainfall measured during the preceding year, so the moisture will be important. A higher level of drought relief would be indicated in the forecast if there were indications of good follow-through rains after mid-January.

The forecast for some improvement in the plains is based on a compromise between beneficial rain and snow seen in the first 2 weeks of the forecast period and lower prospects for improvement indicated by the CAS seasonal soil moisture and precipitation forecasts. The Palmer Drought Index probabilities for April suggest that the odds for improvement are relatively slim from northwestern Kansas into western Nebraska, and this area is shown as drought persisting. However, some rain or snow should hit all of the Plains region during the first 2 weeks, given the forecast transition to a deep upper level trough digging into the central United States by late January.