Jul 19, 2012

Downward spiral of drought conditions in Midwest... National Drought Summary -- July 17, 2012

Downward spiral of drought conditions in Midwest... Monte

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 National Drought Summary -- July 17, 2012

The discussion in the Looking Ahead section is simply a description of what the official national guidance from the National Weather Service (NWS) National Centers for Environmental Prediction is depicting for current areas of dryness and drought. The NWS forecast products utilized include the HPC 5-day QPF and 5-day Mean Temperature progs, the 6-10 Day Outlooks of Temperature and Precipitation Probability, and the 8-14 Day Outlooks of Temperature and Precipitation Probability, valid as of late Wednesday afternoon of the USDM release week. The NWS forecast web page used for this section is: http://www.cpc.ncep.noaa.gov/products/forecasts/.

Weather Summary: A strong upper-level ridge of high pressure dominated the nation’s weather this U.S. Drought Monitor (USDM) week, bringing well above-normal temperatures to the central and northern tier states. Clouds with scattered showers and thunderstorms along a stalled cool front kept temperatures below-normal in the southern states. But even then, maximum temperatures were 90 degrees F or warmer across much of the country, with maximums exceeding 100 from South Dakota to Kansas. Philip, South Dakota, reached 109 degrees on July 15. Beneficial rain fell from southern Texas to the southern Appalachians along the front. Excessive rainfall occurred over southeast Texas where amounts totaled 10 inches or more in places, but elsewhere rainfall amounts were generally localized with limited relief. Monsoon showers and thunderstorms brought above-normal rain to parts of the West, but the rain had little impact on deficits which have accumulated over several months. Weak fronts triggered localized showers and thunderstorms along the northern tier states. In between, hot and dry weather dominated from the central Plains to Ohio Valley, Great Lakes, and Northeast.

Another week of hot and dry weather continued the deterioration of crop conditions in America’s breadbasket. U.S. Department of Agriculture (USDA) reports for the week ending July 15 indicated that 38 percent of the nation’s corn crop was in poor to very poor condition, compared to 30 percent a week ago, and 30 percent of soybeans were in poor to very poor condition (compared to 27 percent last week). Fifty-four percent of the nation’s pasture and rangeland was in poor to very poor condition, which is a jump of 4 percent compared to last week and is an all-time high for the 1995-2012 growing season weekly history. About two dozen large wildfires, mostly in the West, were burning on July 17, about half the number compared to a week ago. Streamflows were in the lower tenth percentile of record, or at record low values at several time scales, across much of the Midwest and parts of the central Plains, West, Southeast, and even parts of New England. As a result, the impacts boundaries were shifted to reflect short-term and long-term drought conditions from the west coast to Ohio Valley and Southeast, with short-term conditions indicated in the northern tier states and from eastern Tennessee to New England. Long-term impacts were indicated for parts of the Southwest and central Gulf of Mexico states.

The Northeast and Mid-Atlantic: Light to locally moderate rain fell across parts of the region. But even the heaviest amounts, which fell in southeastern Pennsylvania and extreme southeast New York, were barely above normal for the week. Most areas were drier than normal and hot, with abnormally dry (D0) conditions expanding across New York, southern New England, northern Pennsylvania, and northern New Jersey. Moderate drought (D1) spread eastward from western New York, grew in the Chesapeake Bay area, and was added to western Massachusetts.

The Southeast, Deep South, and Southern Texas: Widespread heavy rains and flooding in southeast Texas resulted in significant improvement with the USDM depiction improving by two categories in parts of Texas and adjacent Louisiana. Elsewhere along the front, drought conditions improved by one category in a few local areas where 2-3 inches, or more, of rain fell, from Mississippi and southern Arkansas to West Virginia, and from Georgia to North Carolina. But expansion occurred in a few local areas missed by the rains in Alabama and North Carolina. Exceptional drought (D4) expanded in western Kentucky and southern Illinois, severe drought (D2) expanded in northwest Kentucky, and D1 filled in the hole from northern Kentucky into southwest Ohio. D1 expanded in the Florida panhandle which had below-normal rainfall and where low lake levels persisted.

The Great Plains to Midwest: Unrelenting heat and lack of rain continued the downward spiral of drought conditions. D0 to D2 expanded across parts of the Plains from Texas to North Dakota, from Missouri to Minnesota, and in the southern Great Lakes. Extreme drought (D3) was introduced in Nebraska, Missouri, and Wisconsin, and D3 expanded in Arkansas, Oklahoma, Kansas, and Indiana. The city of Indianapolis, Indiana, implemented mandatory water restrictions for the first time ever with many trees dropping their leaves and going dormant months early. Exceptional drought (D4) expanded in Arkansas and was introduced in western Kansas.

The West: Monsoon showers held drought deterioration at bay across much of the West, but with amounts mostly an inch or less, little improvement was seen. Even the 2+ inch rains in parts of Arizona were not enough to change the drought depiction. D4 in northwest Colorado was removed as conditions improved from recent rains, and the D1 was removed and surrounding D0 shrank in central Washington as precipitation in recent weeks justified the reassessment there. But drought conditions deteriorated in other parts of the West. D4 expanded slightly in southeast Colorado, and D0-D2 expanded from southeast Oregon and northern Utah to southern Montana.

Hawaii, Alaska and Puerto Rico: The week was mostly drier than normal at most stations in Alaska and Hawaii, but no change was made to the depiction there. It was another dry week for much of Puerto Rico, with accumulated deficits exceeding 8 inches for the last two months. D0 was added to the western and eastern sections of the island which were persistently drier than normal out to 90 to 180 days and where below-normal streamflows were beginning to appear.

Looking Ahead: Beneficial rains could continue from the Gulf of Mexico coast to Mid-Atlantic States during July 18-23, with amounts in excess of two inches in places. Some of these rains could spread into the eastern sections of the Tennessee and Ohio valleys. Monsoon showers are expected in the Southwest and showers and thunderstorms may develop with fronts moving across the northern tier states, although rainfall amounts should generally be less than an inch in these areas. The southern to central Plains will likely be devoid of precipitation. Temperatures for much of the country east of the Rockies will be above normal, with departures possibly 10 to 15 degrees above normal from the central Plains to Great Lakes.

For July 24-August 1, dry weather is expected to dominate in the southern to central Plains, across the Gulf coast, and along the west coast, while monsoon showers should bring above normal precipitation to the Southwest. Above-normal temperatures should maintain their hold across the interior U.S. from the Plains to Southeast, with cooler-than-normal conditions along the west coast. Alaska is forecast to be wet with above-normal temperatures in the northeast and cooler-than-normal conditions in the west and south.

Author: Richard Heim, National Climatic Data Center, NOAA

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