March - May 2014

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Latest Seasonal Assessment - Much needed precipitation brought limited drought relief to parts of the Northwest, the Great Basin, and the northern Intermountain West, but drought continued to expand and intensify across parts of California, the desert Southwest and the southern Rockies. Outside of spotty precipitation over southern and western Texas, drought also expanded across much of the central and southern Plains, and short term drought developed along the western Gulf Coast. Widespread precipitation brought drought relief to the eastern U.S.

Drought persistence and expansion are anticipated for California, the Southwest, and the southern Plains due to dry initial conditions heading into the climatologically drier Spring season. CPC 1-Month and 3-Month outlooks tilt the odds towards below-median precipitation over parts of the Southwest and California as well. In contrast, short range forecasts for heavy precipitation increase prospects for additional drought relief across the Pacific Northwest and the northern Rockies, although anticipated warmer than normal temperatures may limit effective snowpack building for late spring water resources. Drought improvement or removal is forecast for the central Plains and the middle and upper Mississippi Valley, where climatological precipitation increases substantially during April and May. While locally heavy precipitation is forecast in the short term for parts of the central and western Gulf Coast, which would ease short term drought conditions, the CPC seasonal outlook indicates enhanced chances of below-median rainfall. With 90-day precipitation totals generally below 75 percent of normal, it is possible for short term drought reductions to be offset by redevelopment later in the Spring.

Short range forecasts for enhanced precipitation over Hawaii favor additional drought reduction and a deeper than average snowpack over eastern Alaska increases the odds for drought removal.

Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for March 2014, the long lead forecast for March - May 2014, various short- and medium-range forecasts and models such as the 5-day and 7-day precipitation totals from the Weather Prediction Center, 6-10 day and 8-14 day CPC forecasts, the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, dynamical models (CFSv2, NMME, and IMME), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions. ENSO conditions continue to be and are forecast to remain neutral.

Persistent upper-level ridging across western North America promoted rapid expansion and intensification of long-term drought conditions across California, the Great Basin, the Desert Southwest, and the central and southern Rockies. Despite recent localized precipitation across north central California, as of February 16, the average state-wide water year rainfall was a record low 4.54 inches. Given current conditions, the climatological probability of recovering from these 12 to greater than 20 inch precipitation deficits during the upcoming three month period is one in a thousand, according to the NWS Hanford, CA Local Forecast Office. Severe and extreme drought also expanded across Arizona and New Mexico during the past several weeks. Mid-latitude teleconnections with a slowly evolving base state in the tropics that favors enhanced convection over the western Pacific indicates a continuation of downstream ridging over western North America. Several storm systems are forecast to undercut the ridge during late February and early March. While the heaviest amounts are anticipated over the northern tier of the West, enhanced precipitation could bring some drought relief to northern California, parts of the Great Basin, and the central Rockies during late February and early March. The CPC 8-14 day outlook tilts the odds towards above-median precipitation from northern California through the Four Corners region. The monthly outlook for March favors enhanced precipitation for the northern Great Basin, but tilts the odds towards below-median precipitation for southern California through the southern Rockies. Additionally, enhanced odds for above-median temperatures throughout the forecast period increase the likelihood for below average mountain snowfall, exacerbating the already much below average snow water content values across the Sierras and southern Rockies. Based on the drier spring climatology, the extremely dry initial conditions, and decreased prospects for above average rainfall across most of the Southwest, drought persistence and development are forecast.
Forecast confidence for California, the Desert Southwest, and the central and southern Rockies is moderate to high.

The persistent upper level ridge over the western U.S. also brought abnormal dryness and warmth to the Northwest, resulting in widespread short term drought development and expansion during a climatologically wet time of year. Recent storm systems brought drought relief to parts of Washington, Oregon, and Idaho, although most of Oregon remains in severe (D2) drought. Short and long term drought indicators across much of the Northwest are near normal. Additional precipitation is anticipated in the short term, with WPC 7-day quantitative liquid precipitation forecast totals of 2-4 inches across parts of the Pacific coast, Cascades, and northern Rockies. This pattern is forecast to continue during the Week-2 period, with the CPC 8-14 day outlook maintaining enhanced odds for above-median precipitation across the Northwest. The March monthly outlook tilts the odds towards above-median precipitation across the interior Northwest, while the seasonal outlook maintains equal chances for below, near, or above-median precipitation. Based on the relatively shallow drought conditions and prospects for additional heavy precipitation during late February and March, drought improvement or removal is forecast for the Pacific coast and much of Washington and Idaho. Persistence is maintained across central Oregon and far southwestern Idaho, where mountain snowpacks remain generally below 75 percent of normal. Enhanced odds for above-median temperatures during the outlook period may favor rainfall at higher elevations instead of snow and also promote early spring melting.
Forecast confidence for the Northwest is moderate.

Although localized precipitation brought drought relief to parts of southern and western Texas, generally below normal winter precipitation elsewhere promoted drought expansion and intensification across the southern Plains. The driest conditions occurred over western Oklahoma, with some areas receiving under 25 percent of normal precipitation. Winter is a dry time of year for the Plains, and climatological precipitation increases markedly during the spring. The CPC 8-14 day outlook tilts the odds towards above-median rainfall over southern Texas, and the monthly and seasonal outlooks maintain equal chances for below, near, or above-median precipitation during the outlook period. Although the climatological increase in rainfall during the spring may bring some drought relief to the southern Plains, the dry initial conditions and increased sensitivity to drought development due to multi-year drought conditions supports drought persistence or development across the southern High Plains, with the greatest chances for drought improvement over central Oklahoma and northeastern Texas.
Forecast confidence for the southern Plains is moderate.

While a winter storm brought localized drought relief to northeastern Kansas, HPRCC-based 90-day percent of normal precipitation was below 75 percent across most of Kansas and Nebraska. Drought conditions worsen towards the west, where parts of southeastern Colorado, western Kansas, and southwestern Nebraska remain in extreme to exceptional drought. The percent of annual precipitation increases substantially during the spring across the Great Plains as Gulf moisture penetrates further north and west. CPC extended range and long lead guidance maintain equal chances for below, near, or above median precipitation across the Plains during the outlook period. Based on January Palmer Drought indices and climatology, the NCDC-based probabilities of drought amelioration in four months are above 60 percent for the central Plains, with even below average rainfall sufficient to alleviate drought. Since drought conditions have worsened across the central Plains during February, the confidence in climatological rainfall reducing drought is somewhat lower, particularly across western areas. Therefore, drought improvement or elimination is forecast for Nebraska and much of Kansas, while persistence is maintained for southwestern Kansas and southeastern Colorado.
Forecast confidence for the central Plains is moderate.

Abnormal winter dryness promoted rapid expansion of short term drought across parts of the western and central Gulf Coast during early 2014, although recent heavy rainfall brought some relief to parts of Louisiana. Short term forecasts indicate a high probability for additional heavy rainfall across the central Gulf Coast, with some support in the Week-2 guidance for continued enhanced precipitation over both the western and central Gulf Coast. Since the existing drought conditions are mostly shallow, the wet short term forecasts would promote drought improvement or removal. The CPC seasonal outlook, however, tilts the odds towards below-median rainfall along the western and central Gulf Coast. Lingering long term precipitation deficits make this region susceptible to drought, so any period of abnormal dryness during the spring may promote redevelopment of drought across eastern Texas and Louisiana, similar to what occurred during January and February. Based on the high probabilities for heavy rainfall in the short term coupled with a drier seasonal outlook, drought improvement or removal is limited to areas of Louisiana where the heaviest rainfall is currently forecast. While drought persistence is maintained across the remainder of the western Gulf Coast, it should be noted that short term improvements are possible, with a possibility for dryness returning later in the spring.
Forecast confidence for the western and central Gulf Coast is low.

Generally below-normal precipitation was observed across the middle and upper Mississippi Valley during the winter, although impacts were not substantial due to a dry climatology and frozen soils and streams. Locally heavy precipitation (1-2 inches liquid equivalent) is forecast during the upcoming week for northern Missouri and central Illinois, although the CPC 8-14 day outlook tilts the odds towards below-median precipitation with an arctic air mass in place. Climatological precipitation increases during the spring across the middle and upper Mississippi Valley. Based on the relatively shallow drought conditions, the NCDC probabilities of precipitation required to ameliorate drought during the spring season are above 60 percent for all climate divisions in the Midwest with Palmer Drought Index values less than -2. Therefore, drought improvement or removal is forecast.
Forecast confidence for the middle and upper Mississippi Valley is moderate.

Drought conditions have eased during the winter across eastern areas of interior Alaska. A small area of moderate drought remains over eastern Alaska near the Canadian border. Snow cover in this region is deeper than normal, which favors drought removal, especially once spring melting commences.
Forecast confidence for Alaska is high.

Periods of enhanced rainfall during the winter rainy season have promoted drought reduction across the Hawaiian islands. Small areas of severe drought remain on the Big Island and Molokai. During the upcoming week, dynamical models support the idea of a trough over the northern Pacific entraining ITCZ moisture and bringing enhanced rainfall to Hawaii. Any additional above normal rainfall during the late rainy season would favor further short term drought reduction.
Forecast confidence for Hawaii is moderate to high.