Bloomberg News

U.S. Seasonal Drought Outlook for May 3 to July 31 (Text)

May 03, 2012

Following is the text of the U.S. Seasonal Drought Outlook as released by the National Weather Service in Camp Springs, Maryland:

Latest Seasonal Assessment - The Drought Outlook for May 3 - July 31, 2012 is based on short-, medium-, and long-range forecasts, initial conditions, and climatology. Since the release of the previous Drought Outlook issued on April 19, 2012, a slight expansion of drought occurred in the Tennessee Valley and lower Ohio Valley while drought conditions intensified across the interior Southeast. In contrast, drought improvement is noted across southern New England and southeast Florida. Since precipitation signals are weak on the seasonal time scale, this outlook is based primarily on short to medium range forecasts and climatology. Some improvement is forecast along the East Coast with improvement most likely across the south-central Florida peninsula. The protracted drought across Georgia and South Carolina is expected to persist. Persistence is also forecast in northeast Minnesota, but prospects for improvement increase farther south in southern Minnesota and northern Iowa. Some improvement can be expected across the drought areas of the central and southern high Plains, while drought is expected to persist or expand across parts of the West along with western and south-central Texas. A drier climatology supports persistence in Hawaii.

Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for May 2012 and the long lead forecast for May through July 2012, various medium- and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the most recent 384-hour GFS total precipitation amounts, the soil moisture tools based on the Constructed Analog on Soil (CAS) moisture, the Climate Forecast System (CFS, versions 1 and 2), the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

During the early spring, drought coverage increased while ongoing drought intensified across the interior Southeast due to a lack of adequate precipitation (departures of 2-4 inches below normal), above normal temperatures, and increased evapotranspiration rates. Mostly dry weather coupled with record heat (maximum temperatures into the 90s) during the first week of May is expected to result in worsening of drought conditions across Georgia and South Carolina. Persistence is forecast for this area of protracted drought across most of Georgia and South Carolina where no wet signals are apparent among precipitation tools at the seasonal time scale. Climatologically, rainfall increases slightly closer to the Gulf Coast and some improvement is forecast for the Florida Panhandle. Meanwhile, frequent and locally heavy rainfall recently led to drought elimination in southeast Florida. Improvement is most likely to continue across south-central Florida due to an increasingly wet climatology during June and July. Forecast confidence for the Southeast is moderate.

Small areas of moderate drought developed in Illinois, western Kentucky, and middle Tennessee during April and the beginning of May. Some improvement is forecast for Illinois since the drought is short-term, moderate to heavy rainfall is expected in the short-term, and the CPC May and May-July outlooks call for equal chances of above, near, or below median precipitation. Across western Kentucky, precipitation is less than 50 percent of normal during the past 120 days. A more pessimistic forecast exists for western Kentucky since short-term rainfall is less certain and precipitation anomalies are much larger than across Illinois. Some improvement is forecast for the newly developed drought area in middle Tennessee since near to above median rainfall is favored during the next ten days and the May-July outlook calls for equal chances of above, near or below median precipitation. Forecast confidence for Illinois, western Kentucky, and Tennessee is low.

An unusually warm and dry March resulted in rapid development of moderate to severe drought from the Delmarva region north to New England. Although precipitation signals are weak on most time scales, some improvement is based on the short duration of drought conditions that can be eased with more seasonal rainfall. Forecast confidence for the mid-Atlantic, Northeast, and New England is moderate.

In the upper Midwest and northern Plains, May - July is climatologically one of the wettest times of the year. Typically 35 to 45 percent of annual precipitation falls during this 3- month period from the eastern Dakotas eastward through Iowa and Minnesota, climbing to between 45 and 60 percent in the northern Plains. Improvement is forecast across southern Minnesota and Iowa due to a favorably wet climatology and heavy rainfall during the first week of May. Prospects for improvement decrease across northeast Minnesota with lighter short-term rainfall and a longer term drought. Some improvement for the northern and central high Plains is based on a wet climatology and enhanced odds for near to above median precipitation during the 6-10 day period. Forecast confidence for southeast Minnesota/northern Iowa is high and for the remainder of Minnesota and the northern Plains is low.

Drought is expected to persist across much of the West and expand across the central Rockies and south-central Texas. May- July is a relatively wet time of year for the southern High Plains and neutral to dry farther west, especially in the desert Southwest and California. A slight tilt in the odds towards below median precipitation is forecast for May-July across the north-central Rockies with no discernible tilt of the odds farther south. Surface moisture is depleted in late spring and summer across this region due to the frequency of hot, dry, and windy weather. In addition, mountain snowpack, the source of a lot of the region’s moisture, is starting off below normal, and as a result summer streamflows are expected to be abnormally low. In addition, May - July is expected to be warmer than normal, potentially enhancing the typical surface moisture depletion that always happens during this time of year. The result is a forecast for persisting drought that could expand into the central Rockies if there is sufficiently enhanced seasonal surface moisture draw-down. Onset of monsoonal rains in July should improve surface moisture levels in southeast Arizona and southwest New Mexico, resulting in a forecast of some improvement in these areas. Beneficial rainfall expected during early to mid-May along with a relatively wet climatology (30 to 40 percent of annual precipitation occurs from May-July) supports some improvement across southwest Kansas. Forecast confidence across the southwestern and western parts of the nation is high.

Following drought improvement across parts of Texas during the late winter and early spring, a drier pattern returned during April. Although no dry signals are apparent among the seasonal precipitation tools, a lack of rainfall during April into early May (typically a wet time of year) across south-central Texas combined with enhanced odds for above normal temperatures from May-July supports persistence and development across south- central Texas. Persistence is also forecast across west Texas due to expected abnormal warmth in the May-July outlook. Odds for improvement increase across northwest Texas due to a favorable pattern for beneficial rainfall during early-to-mid May. Enhanced odds for above median precipitation are forecast in the CPC 6-10 day outlook, valid from May 8-12, across northwest Texas. Forecast confidence for Texas is moderate.

Hawaii is transitioning into its drier time of the year and thus persistence can be expected. Although not designated on the USDO map, a small area of some improvement may occur along the Kona slopes. Forecast confidence in Hawaii is moderate.

SOURCE: National Weather Service

To contact the reporter on this story: Stephen Rose in Washington at kmckeaney@bloomberg.net

To contact the editor responsible for this story: Marco Babic at mbabic@bloomberg.net


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