Bloomberg News

U.S. Seasonal Drought Outlook for Aug. 16 to Nov. 30 (Text)

August 16, 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 - Drought covered over 60 percent of the contiguous 48 states as of mid-August 2012, although significant expansion finally halted during the last couple of weeks. Still, almost one-quarter of the country was experiencing extreme to exceptional drought (D3 - D4 on the Drought Monitor), primarily in a large swath generally extending from the central Rockies eastward through the Mississippi and Ohio River Valleys. Many locations from Indiana, the western reaches of Tennessee and Kentucky, and Arkansas westward through parts of Iowa, central Kansas, and eastern Oklahoma received 8 to 12 inches less precipitation than normal April 1 - August 14, 2012, with a few areas reporting deficits exceeding one foot. According to the U.S. Department of Agriculture, 51 percent of the corn crop was in poor or very poor condition across the 18 primary corn- producing states, as was 48 percent of sorghum (11 primary producing states) and 38 percent of soybeans (18 states). For the contiguous 48 states as a whole, 59 percent of pastures and rangelands were in poor or very poor condition, with 4 states reporting more than 90 percent of their pastures and rangelands in poor or very poor condition (Missouri 98 percent, Illinois 94 percent, Nebraska 92 percent, Kansas 90 percent) and another 6 states topping 85 percent. The Drought Outlook valid through the end of November 2012 indicates drought conditions will remain essentially unchanged in large sections of the central Mississippi Valley, the central and southwestern Great Plains, most of the High Plains, the central Rockies, the Great Basin, and parts of the Far West, though the seasonal declines in temperatures, evaporative moisture loss, and water demand should preclude any widespread worsening of conditions. At least some improvement is forecast for much of the central Rockies, the Southwest, the southern Great Plains, the Ohio Valley, the Great Lakes region, the upper Midwest, and the eastern tier of states. In Hawaii, the odds favor cooler- and drier-than-normal conditions through the rest of the year as a whole, which should cause drought to persist and expand through most of the state except for eastern sections of the Big Island. The developing El Niño episode, expected to last through the winter, could begin to bring above-normal precipitation to parts of the southern and eastern states late in the period. Discussion for the Seasonal Drought Outlook

Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for September 2012 and the long lead forecast for September through November 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.

For the eastern tier of states, improving conditions are expected both in the Southeast and Northeast, some improvement is expected across the interior mid-Atlantic region, and persistence is expected in Delaware and adjacent Maryland. The odds favor above-normal rainfall through the last half of August in all these areas, and the long-lead forecast leans wet in western Georgia and adjacent Alabama. The southeastern drought region has been slowly improving for a number of months now, and given short-term forecasts and the potential for the developing El Niño to bring enhanced rainfall to the region late in the period, improvement is the logical forecast. In the Northeast, the expected wetness during the last half of August, the seasonal drop in temperatures (inducing less surface water evaporation and reduced water demand) and the potential for snow late in the period (which can efficiently replenish soil moisture content) all argue for improvement there. The interior mid-Atlantic region is less clear-cut given the milder autumn temperatures (relative to the Northeast) and the lack of a strong correlation between El Niño conditions and precipitation during this period, so a forecast of some improvement seemed most prudent. In the coastal mid-Atlantic region, significant precipitation deficits date back a couple of years if not more. Here, drought conditions should persist given the amount of precipitation necessary to substantially reduce large, long-term precipitation deficits Forecast confidence for the Eastern States is high in the Northeast and Southeast, and moderate in the mid-Atlantic region.

For the large area of drought covering areas from the High Plains eastward through much of the Mississippi and Ohio River Valleys, the forecast is difficult to say the least. Above- normal precipitation (indeed, locally heavy rainfall) is expected during August 16 - 21, 2012 in the southern tier of the region from central and eastern Texas eastward; odds favor above-normal precipitation for the remainder of August from southern and eastern Texas, the lower Mississippi Valley, the Ohio Valley, and the eastern Great Lakes region eastward to the Atlantic Coast; and the long-lead outlook for September - November 2012 indicates enhanced chances for above-normal precipitation in eastern Texas, Louisiana, and Alabama. Farther north and west, near- to below-normal precipitation seems more likely in the High Plains and northern half of the Great Plains for the last half of August, and the September - November outlook leans neither dry nor wet. These precipitation considerations are rather straightforward, but what complicates matters is the seasonal decline in temperatures, which brings with it reduced evaporative water loss, lower water demand, and declining vegetative need for soil moisture. This consideration is particularly important this year given how excessive summer heat amplified and accelerated drought development in the central United States. In the end, improvement was forecast in southern Texas (where both weeks during the last half of August could be quite wet), the lower Mississippi Valley (where odds favor a wet September - November), the Ohio Valley and eastern Great Lakes region (where wet weather is favored in late August, and where the seasonal temperature decline could have a significant effect), and the upper Midwest and northern Plains (primarily for a more marked effect from cooler autumn temperatures, and because precipitation deficits do not date back quite as far as in many other areas). Some improvement was forecast in areas adjacent to these improvement regions, and persistence was forecast effectively for the interior and western parts of this large drought region. However, the effect of cooler autumn weather is not easy to determine, and given the indeterminate precipitation forecast, improvement could well be felt in a considerably larger part of this region. The most likely area for persistence is across southern Nebraska, Kansas, Oklahoma, and the southern High Plains, where near or below normal precipitation is anticipated in the short term, the September - November period leans neither wet nor dry, autumn temperatures are relatively mild, and excessive heat has been felt more recently than in areas farther east, north, and even south. Forecast confidence is low through most of the central United States, but moderate in Kansas, Oklahoma, and the southern half of the High Plains.

From the Rockies westward, improvement was forecast for much of Arizona and adjacent portions of southern California, southeastern Utah, southwestern Colorado, and western New Mexico. A fairly narrow area of some improvement surrounds the improvement area, with drought expected to persist farther north and west, as well as in central New Mexico. The September - November outlook identifies enhanced chances for above-normal precipitation in the Southwest, leading to a forecast of improvement there. Just to the north and northeast of this region in southwestern Colorado and nearby areas, this is a fairly wet time of year, so the chances for improvement are fairly good, especially as autumn temperatures decline. Elsewhere in the West, however, the last half of August looks dry, and the 3-month outlook favors below-normal precipitation in central California, northwestern Nevada, Oregon, and adjacent Idaho. In addition, mountain snow water content is one critical indicator of drought given the way water is managed in the West and the ecology of the region. Precipitation during September - November has little impact on mountain snow water content, which typically peaks in the spring, and thus drought tends to change little during this time of the year. Forecast confidence from the Rockies westward is high, except moderate in and near the improvement area across southwestern Colorado and immediately adjacent areas in Utah, New Mexico, and Arizona.

Most indicators point toward cooler and drier than normal weather prevailing across Hawaii for the rest of the year as a whole. Therefore, drought is expected to persist where it already exists, and expand to cover most of the state (except the eastern Big Island) by the end of November. Forecast confidence for Hawaii is moderate.

SOURCE: National Weather Service

To contact the reporter on this story: Stephen Rose in Washington at srose31@bloomberg.net

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


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