U.S. Seasonal Drought Outlook for June 2 to Aug. 2011 (Text)
Latest Seasonal Assessment - A classic and very persistent La Nina precipitation pattern has dominated the country since Autumn 2010, resulting in broad areas of drought across the southern tier of states, in the southern half of the Plains, and along parts of the lower and middle Atlantic seaboard. Extreme to exceptional drought covers most areas across the southern Rockies, the central and southern Plains, the immediate Gulf Coast, and the southernmost Atlantic seaboard. Drought has been most acute through Texas and the southern High Plains, where many locations experienced the driest October through May period on record, in some places by wide margins. Frequently high wildfire danger, dramatic agricultural impacts, and increasing hydrologic concerns have been felt throughout these areas. Farther east, drought dates back more than a year from much of eastern Texas and Louisiana eastward through northern Florida and southeastern Georgia even as an historic influx of water from the north flooded rivers and the extensive marshlands in parts of Louisiana.
The La Nina precipitation pattern should loosen its grip through the meteorological summer of 2011, leaving a lot of uncertainty about how drought conditions will evolve by the end of August 2011. The Drought Outlook map was synthesized from a combination of initial drought conditions, current drought duration, forecasts for the first two weeks of June, the June monthly forecast, and climatology (especially whether June - August is a relatively wet or dry season) to varying degrees. Drought is expected to persist in the interior Carolinas and through much of Louisiana and adjacent areas, where drought dates back farther than in most other areas. In other existing areas of drought, the odds at least nominally favor some degree of improvement, though there is nothing pointing toward anything broad-scale and substantial. To wit, the forecasts of “some improvement” and “improvement” for the parched areas of Texas and the southern High Plains were driven by the approach of a neutral to climatologically wet season (summer) which should provide at least some surface moistening, even if amounts aren’t unusually heavy. There is nothing to indicate that widespread, significant drought relief should be expected during the forecast period, though that of course is a possibility; in fact, prior to any seasonal increase in rainfall across the southern High Plains, conditions may well get worse before they get better.
Discussion for the Seasonal Drought Outlook:
Tools used in the U.S. Drought Outlook (USDO) included the official CPC precipitation outlook for June 2011 and the long lead forecast for June - August 2011, 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 Analogue on Soil (CAS) moisture, the Climate Forecast System (CFS) seasonal precipitation forecasts, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.
The Drought Outlook valid through the 2011 meteorological summer (August 2011) anticipates a slow dissolution of the classic La Niña precipitation pattern across the contiguous United States dating back approximately to October 2010. This pattern has covered the southern tier of the country from Arizona eastward through Florida, parts of the southern and middle Atlantic Coast, and the southern half of the Plains in drought. Extreme to exceptional drought covers many areas from southeast Arizona and central New Mexico eastward through Florida and southern Georgia, and much of the central and southern Plains. Precipitation has been most critically lacking in much of Texas and the southern High Plains, where October through May totals were unprecedentedly low in many areas.
With the unwavering La Niña pattern expected to wane as summer 2011 progresses and the typical decline in long-lead precipitation predictability during this time of year, there is a sharp drop in Drought Outlook confidence nationwide compared to the forecasts issued between September 2010 and April 2011. In fact, the June - August 2011 long-lead forecast indicates no tilt of the odds toward either above- or below-normal precipitation in any of the areas currently experiencing drought (except in Hawaii). As a result, the June - August 2011 Drought Outlook leans primarily on initial drought conditions, the day 1 through 14 forecasts, the June 2011 monthly forecast, and climatology.
From southern Mississippi northeastward into the lower mid- Atlantic coast, Light precipitation is expected through early June, and the odds favor below-normal rainfall along the Gulf Coast through southeastern Georgia into the middle of June. June - August is climatologically a little wetter than other times of the year along the immediate coasts and the southeastern half of Georgia; however, drought is well entrenched in southern parts of this region, dating back more than a year. Given these factors, drought is forecast to persist near the Gulf and in southeast Georgia, with limited improvement expected in most other areas. Farther north, drought is also expected to persist in the central Carolinas with some improvement anticipated farther east, where dryness has been of shorter duration. Confidence in the Southeast and along the eastern Gulf and southern Atlantic coasts is low.
Drought has also gripped the Florida Panhandle to varying degrees for the past several months, which coincides with its driest time of the year. The odds favor below-normal rainfall in northern areas through mid-June, and near- to above-normal amounts farther south. The advent of the rainy season in June should at least alleviate any surface moisture shortages existing at that time, even if June - August 2011 totals are unremarkable. Confidence in the Florida Panhandle is high.
In the lower Mississippi Valley, seriously deficient precipitation has fallen since Autumn 2010, and consistently below-normal amounts date back well over a year through much of Louisiana even as upstream rains led to historic flooding along rivers and across the swamps, marshes, and natural levees that cover most of southeastern Louisiana. Given the serious, protracted rainfall deficits in place and unlikely to change substantially over the summer, drought is expected to continue. Light to moderate rain is expected through June 6, with more than 0.5 inch forecast near the Louisiana Gulf Coast. Odds tilt only nominally toward drier than normal conditions thereafter through mid-June. June - August is climatologically neither a wet nor dry time of year; however, the entrenched and long-term nature of precipitation deficits in this area will not respond readily even to increased precipitation. Confidence in the lower Mississippi Valley is moderate.
The southern half of the Plains states, and in particular the southern High Plains, are experiencing the most acute drought conditions in the country. Even though dryness dates back only to last October, the period since then has brought record dryness to many locations, with some parts of western Texas and eastern New Mexico recording only a few tenths of an inch during the period. Serious and intensifying agricultural impacts and frequently high wildfire danger has been a mainstay for several months now, and longer-term hydrologic impacts have been on the rise. A few tenths of an inch of rain is expected by June 6 across Kansas, eastern Colorado, and much of New Mexico. Through mid-June, drier than normal conditions appear likely regionwide. Subnormal rainfall may continue through June across Texas, but for the summer as a whole, the only indicators of which direction the drought will take are initial conditions and climatology. The outlook for the swath of land from central parts of Texas, Oklahoma, and Kansas westward through the southern High Plains was driven exclusively by initial conditions and climatology. Western and northern parts of this region are headed into their wet season as summer progresses, making it likely that at least some surface moisture improvement will be felt by the end of August, though this forecast should not be interpreted as calling for widespread, significant relief, and conditions may well get worse before they get better. From central Texas into south-central Oklahoma, where June - August is not particularly wet and/or precipitation since the start of the water year has been particularly sparse, limited improvement is expected at best, even if it is only a marginal boost in surface moisture. Persistence is only forecast in eastern Texas, where drought dates back farther than in the rest of the region. Confidence in the southern half of the Plains is moderate.
Drought also covers the Southwest from western New Mexico through central Arizona. A few tenths of an inch of rain is expected in western New Mexico through early June, but generally drier than normal conditions are expected areawide through the middle of the month, although this is a dry time of year for the region anyway. Later June through August tends to be wetter climatologically, though not to the extent observed a little farther to the east. The result of these considerations is a forecast for some improvement. Confidence in the Southwest is low.
In Hawaii, there are enhanced chances for drier than normal June - August conditions, resulting in drought conditions similar to or slightly worse than at the start than at the start of June. Confidence in Hawaii is moderate.
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