February-April 2005

Latest Seasonal Assessment - The latest seasonal drought outlook continues to call for generally improving conditions across the Southwest and central Great Basin, while prospects for relief diminish farther north. Drought will tend to persist from southeastern Oregon eastward through Idaho into Montana, northern Wyoming, and the western Dakotas. Limited improvement is expected in a transition zone between the two areas. Current low snowpack and a long-range outlook for below-normal precipitation during February through April placed the Pacific Northwest at enhanced risk for drought development, notwithstanding recent heavy rains in some areas. As of January 19, the water content of high-elevation snowpack stood at less than one-half of normal across much of Washington and northern Oregon, and less than two-thirds of normal in north-central Idaho. Forecasts for above-normal precipitation during the latter half of January mitigate the drought threat to some extent, especially in Washington. Farther south, epic snowstorms in late December and early January resulted in enormous snowpack increases from California across the Great Basin and the Four Corners area. This sets the stage for increased streamflows into area reservoirs during spring and summer as well as replenished groundwater supplies and soil moisture. With the official Climate Prediction Center outlook calling for enhanced odds for above-normal precipitation during February-April from California through New Mexico, additional improvement in the long-term drought is expected, although some larger reservoirs will likely take a long time-perhaps several years-before storage gets back to normal. Elsewhere, little drought improvement is anticipated in the upper Missouri River Basin-- including Montana and the western Dakotas--through April. Farther east, there has been sporadic dryness since October along the Southeast Atlantic coast from the Carolinas to Florida. Drought is not forecast at this time, but the area bears watching. In Hawaii, recent heavy rains have reduced the threat of drought development.

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for February-April, the drought termination and amelioration probabilities for April, 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 Analogues for the season, and the latest western water supply forecasts.

The current drought outlook focuses on the February-April precipitation outlook and considers current mountain snowpack and the latest official spring and summer western streamflow forecast from USDA and NOAA. The huge snowstorms that struck the area extending from California into the Southwest and Great Basin in late December and early January have contributed to unusually high snow water content levels as of mid-January, with several river basins exceeding 200 percent of normal, and many over 150 percent of normal. As a result, the January 1 streamflow forecast showed normal to above-normal flows from California eastward into the Four Corners region for this spring-summer season. With much of this region slated to see above-normal precipitation in the next 2 weeks as well as the February-April period, additional drought relief can be expected. Relief is expected to be more limited in northern New Mexico due to lower snowpacks accrued so far this season. Optimism is somewhat tempered by short-term forecasts for above-normal temperatures across the West as well as the February-April outlook for above-normal temperatures, although the probabilities for warmth are muted outside of the Pacific Northwest in the latter outlook.

The drought outlook for much of the West is quite similar to the one from December, although the odds of seeing storms similar to those that hammered the region in late December and early January are very slim, so improvement may not be as substantial. As before, it should be noted that significant water storage increases are not expected in coming months in the large Colorado River Basin reservoirs. The good news is that snowpack in the watersheds above Lake Powell was close to 140 percent of normal in mid-January, providing hope for normal or better inflows during spring snowmelt season. The bad news is that Powell was only 35 percent full and its elevation was 136 feet below capacity, so it's a long road back to full recovery. In New Mexico, relatively lower expectations for relief from hydrological drought due to lower snowpack numbers resulted in the area of limited improvement in northern areas. The severity and length of the ongoing drought in northern parts of the state was a consideration as well.

The main change from the previous drought outlook was in the Pacific Northwest, where continued low snowpack and the outlook for below-normal precipitation and above-normal temperatures in February-April heightened the odds for drought development. Recent heavy rains and forecasts for more precipitation in January have reduced the drought threat in parts of the region, especially in Washington, but it should be noted that water managers prefer to see snow rather than rain, so recent and forecast rains may not provide as much benefit as precipitation falling in the form of snow. Snow water content ranged from 25 to 64 percent of normal in Washington as of January 19, and 22 to 80 percent of normal in most of Oregon. The official long-lead precipitation outlook for February-April depicts a slight tendency toward below normal precipitation in Washington and Oregon, with the greatest odds for dryness in western Washington. The new Drought Outlook weighs the recent flood-inducing rains in western Washington and forecasts for more precipitation in the next 2 weeks in the region against the current low snow water content and drier long-range outlook to arrive at the depiction of the drought threat extending across Oregon and central Idaho and parts of Washington.

The new Drought Outlook continues to call for persisting drought in the upper Missouri Basin. Neither medium-range nor long-range forecast models show much inclination toward improvement from the ongoing long-term drought, with the latest Coupled Forecast System (CFS) depicting below-normal precipitation and above-normal temperatures for February-April in eastern Montana and the Dakotas. In contrast, the latest Constructed Analogue forecasts from soil moisture (CAS) show wetness for the same time period, so confidence for this region is low, consistent with the official February-April outlook showing equal chances of wet or dry. Rain typically picks up in this region in April and more so in May, so the Outlook may be more positive next month, when the target period extends to May.

Extremely wet conditions over much of the country east of the Mississippi preclude drought worries anytime soon, but the tendency for below-normal rainfall seen since October from the Carolinas to Florida bears watching. The time of the year and the lack of a strong seasonal signal for either above-normal temperatures or below-normal rainfall in February-April prevents the introduction of a drought development area at this time.

In Hawaii, recent heavy rains have reduced the chances for drought development, so no development is shown in this month's Drought Outlook despite some indications for below-normal rainfall next season.