U.S. Drought Monitor Report for the Week Ending Sept. 3 (Text)Stephen Rose
Following is the text of the weekly U.S. Drought Monitor as released by the National Drought Mitigation Center in Lincoln, Nebraska:
Weather Summary: The week commenced with high pressure over the Southeast and storm systems traversing across the northern U.S. As the week progressed, the high pressure system traveled westward, settling over the south-central Plains while a trough of low pressure and associated cold front brought scattered showers and thunderstorms to the eastern third of the Nation. A weak frontal system generated scattered showers in the Pacific Northwest. In the Southwest, tropical moisture from Tropical Storm Juliette (which dissipated off central Baja California) helped to fuel the southwest monsoon in Arizona, Nevada, Utah, and southern Idaho. Decent showers also fell on parts of New Mexico and Colorado. Hit and miss showers also fell on parts of the northern Plains and upper Midwest, the central Great Plains, and south-central Texas. Unsettled weather and decent precipitation also affected most of Alaska, with many stations reporting weekly totals exceeding 2 inches in southwestern and south-central sections of the state. In contrast, little or no rain fell on most of California, Oregon, and eastern Washington, parts of the Plains, most of the Mississippi Valley, and much of Hawaii. Weekly temperatures averaged well above normal (6 to 10 degF) across much of the contiguous U.S., with the exception of seasonable readings in the desert Southwest and Southeast. Highs topped triple-digits in the southern two-thirds of the Plains, southern Iowa and northern Missouri. The Northeast: Two to three inches of rain fell across northern Pennsylvania, erasing 60- and 90-day deficits and trimming the northern portion of last week’s D0 area. Just to the south and northwest, however, less than 0.5 inches fell. With only 50-70% of normal precipitation occurring the past 2 months, 2 to 4 inch deficiencies have accumulated. Accordingly, the D0 area was adjusted southward, and a new D0 was added in northwestern Pennsylvania. Although stream flows have yet to be impacted by the short-term dryness, Pennsylvania pasture conditions rated poor or very poor increased by 6 points to 19%, according to USDA/NASS as of September 1. Other areas to watch for future short-term dryness include parts of New York state, Long Island, and Maryland. The Midwest: Well above-normal temperatures (6 to 10 degF), continued lack of rain, and record to near-record low August rainfall in some areas has led to rapidly declining topsoil moisture conditions in parts of the Midwest. After such an ideal start to the growing season (March-June; polar opposite compared to last year), the past two months have been much drier than usual, with temperatures slowly increasing. The region from the eastern Dakotas southeastward into western Illinois (and slowly creeping eastward) has gone from nothing (not even D0) to D1-D2 since mid- to late July, aided by 25-50% of normal rainfall. Some portions in central Iowa and northern Missouri have measured between 5-25% of normal, with some stations in the latter area recording under 0.1” of rain during August. In Iowa, the state recorded its warmest week since July 2012, with highs topping 104F at Des Moines and Fort Madison on August 30. Statewide August rainfall ranked seventh driest among 141 years of records, and followed the ninth driest July. Many Iowa stations set new August records for dryness (Keokuk and Mount Pleasant 0; Burlington and Fort Madison Trace; Jefferson 0.04 in; Centerville 0.1 in; Iowa City 0.13 in; Marshalltown 0.17 in). In the eastern Dakotas, and from northwestern Minnesota into southwestern Wisconsin, only 5-25% of the normal August rain fell. With the addition of the excessive heat, crops and pastures conditions have begun to rapidly deteriorate. According to NASS/USDA (Sep. 1), the percent of corn/soybean/pastures rated very poor or poor were: Iowa 25/24/52; Wisconsin 24/23/56; Minnesota 14/14/45; Missouri 27/27/20; and Illinois 14/13/29. Even USGS stream flows have dropped into the below average (10- 24) percentiles, with some gauges in southern Iowa below the tenth percentile. As a result, D2 expanded or was added in southern Iowa, western Illinois, and northern Missouri, in western Wisconsin, and central Minnesota. D1 increased into southwestern Wisconsin and central Illinois, with D0 added to parts of Indiana and southern Wisconsin. A few areas, however, received over 2 inches of rain, and some improvement was made - northeastern Minnesota, northern Wisconsin, northern Illinois, and southern Indiana. The Lower Mississippi Valley: Little to no rain fell across the Delta (except in northwestern Mississippi), adding to growing short-term deficits over the past 90 days. With 50-75% of normal rainfall the past 3-months, precipitation shortages have reached 4 to 8 inches, and locally to 12 inches. As a result, the D0-D2 areas crept eastward, with D2 reaching into central Mississippi where less than 50% has fallen since June 5. USGS stream flows have dropped below the tenth percentile in parts of central and western Louisiana. In northwestern Mississippi, however, 1.5 to 2.5 inches of rain was enough to reduce short-term deficiencies and improve D2 to D1. Northern and Central Great Plains: Most of the Dakotas reported light to moderate (0.5 to 1.5 inches) of rain, with a few spots in southern North Dakota and northern South Dakota measuring over 2 inches. The rains were enough to keep conditions status- quo, except where the heavier rains fell. In the latter case, D0 was alleviated along most of the western D0 edge of the Dakotas, with D1 to D0 in south-central North Dakota. A slight increase in D0 was made in extreme southeastern South Dakota where many days in the 90’sF have started to prematurely brown the crops. USGS stream flows are still near or above normal at most sites in the Dakotas. No changes were made in Nebraska and Kansas, except for a small 1-category improvement (D1 to D0; D0 to nothing) in extreme sections of southeast Nebraska, northeast Kansas, southwest Iowa, and northwest Missouri, where 1.5 to 3.2 inches fell. Southern Great Plains: In Oklahoma and Texas, several weeks of mostly dry and warm weather (highs in the 100sF) have diminished the surplus rains from a wet and cool July (in both states) and a wet and cool early August (in Oklahoma). As a result, D0 returned across northern Oklahoma, while a 1-category downgrade occurred across southern Oklahoma as August was a no-show in the southern third of the state. In Texas, a band of light to moderate, with some locally heavy (>2 inches) rain, fell from near Del Rio northeastward into southeastern Oklahoma, and along the Gulf Coast. Some slight improvements were made where the heaviest totals occurred. In eastern Texas, little or no rain fell, and some deterioration was made. The Southwest: A continued robust summer monsoon, aided by a northward fetch of moisture from former Tropical Storms Juliette and Kiko (both dissipated west of central Baja California), produced widespread showers and thundershowers to much of Arizona, New Mexico, Nevada, Utah, and northward into parts of the West (Idaho, Wyoming, and Colorado). Numerous locations in southern Nevada and Arizona measured over 2 inches of rain, while 1 to 2 inches were common in central Nevada, western and central New Mexico, central Utah, and most of Arizona. Although short-term shortages have been greatly eased or eliminated, long-term deficits still lingered. To accommodate the long-term impacts, only slight improvements were made where the greatest rains fell and the long-term deficits (180-days) were noticeably reduced. For example, enough rain has fallen during the past 6- months in western New Mexico and southwestern Texas that surpluses have accumulated, hence the D2 to D1 and D0 to nothing upgrade, respectively. Similarly in south-central Nevada, D3 and D2 was improved where there was heavy weekly rains and the 180- day deficits were noticeably diminished. The same holds true in western and central Arizona where D2 and D1 were decreased. On Sep. 2, even many USGS stream flow gauges in western New Mexico, central Arizona, southern Nevada, and southwestern Utah flowed at the 90th percentile at 1- and 7-days. The Impacts line was redrawn to depict improved short-term conditions from the robust monsoon, making the long-term (hydrologic) effects causing most of the negative impacts. The West: Moderate to heavy (1 to 3 inches) rains fell on the Pacific Northwest Coast, effectively eliminating the D0(S) in western Washington. Southwest monsoonal showers also spread northward into southeastern Idaho, central Colorado, and southeastern Wyoming, dropping enough rain (1 to 2.5 inches) to improve D2 to D1 in southeastern Idaho, and 1-category improvement of parts of the D3 and D2 areas in southeastern Wyoming. In addition, 180-day surpluses were present, justifying an upgrade from D1 to D0. Elsewhere, little or no rain fell, and conditions were kept status-quo. An exception was made in north- central Oregon (D0 and D1) where a re-assessment of 90- to 180- day deficiencies were made. The data and products yielded a surplus at those time periods, hence the D1 was improved to D0 (eastern Wheeler county) and D0 removed (from Wasco, Jefferson, Sherman, and western Wheeler counties). Hawaii and Alaska: In Hawaii, the week started and ended dry as only a few Hawaiian stations measured any rain. During midweek, however, scattered showers fell across the windward slopes of the islands, although amounts were light. On Maui, the County Department of Water Supply declared a Drought Watch for Upcountry residents (central Maui) and asked for a voluntary ten percent reduction in water use. Very dry trade winds the past 3 weeks have greatly lowered the stream flow diversions from the northeast-facing slopes of Haleakala that feed reservoirs. Accordingly, D0 expanded across the rest of the island, and D1 pushed into central Maui’s Upcountry. Elsewhere, conditions remained the same. In Alaska, a stormy and unsettled week brought ample precipitation and subnormal temperatures to much of the state. One to 2.5 inches of precipitation was common at many locations across the southern half of the state, with 3 to 6 inches on the Kenai Peninsula and eastward to Cordova. In the central interior, 0.5 to 1.5 inches of precipitation fell. As a result, D0 was removed where the greatest totals occurred (southern portions), D1 was improved a category where over 2 inches fell, and D2 was improved along its southern edge where 1.5 to 3 inches was measured. Looking Ahead: During September 4-9, rainfall is forecast to be along the borders of the contiguous U.S., namely in the Northwest, the Great Lakes region into New England, along the Gulf Coast (Texas to Florida), and in the Southwest. Unseasonable warmth is predicted for much of the country, but especially in the North-Central States. For the ensuing 5 days (September 10-14, 2013), odds for above normal precipitation are greatest in the Southwest, Great Lakes region, Appalachians, and southeastern Alaska. Subnormal rainfall probabilities are highest in the Northwest, southern Plains and lower Mississippi Valley, coastal New England, and western Alaska. Temperatures are expected to be above normal in the western two-thirds of the U.S., Southeast, and southeastern Alaska.
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