Drought - August 2009


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Issued 9 September 2009
Contents Of This Report:
Map showing Palmer Z Index

National Drought Overview

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Detailed Drought Discussion

In total, drought coverage across the United States held fairly constant during August, as small areas of improvement were more or less counter-balanced by regions in which drought emerged or intensified. The end-of-month drought footprint of 14.2 percent (of the contiguous U.S.) was up only slightly from the July value of 13.8 percent. This number remains fairly low relative to the history of the U.S. Drought Monitor (since 1999). In the more intense categories of drought, the overall size of the footprint and the placement of the features remained near constant, with only minor variations.

End of Month U.S. Drought Monitor Image

Three of the nation's most significant ongoing drought episodes persisted or worsened through August. Extreme and Exceptional Drought remained entrenched in Central and South Central Texas. Another drought episode featuring widespread D2 (Severe) Drought persisted in California and Nevada. This Western drought feature expanded to the north during August, where drought emerged or intensified along the Pacific coasts of Washington and Oregon. The eastern islands of Hawaii saw little improvement to drought focused there. A fourth area of Severe to Extreme Drought in Wisconsin and Minnesota improved somewhat, especially in the most intense areas.

The most notable drought eruption came in the desert Southwest, where Moderate (D1) drought emerged across half of Arizona when monsoon rains delivered less-than-typical precipitation. Pockets of Moderate Drought also appeared in the Carolinas.

Precipitation Dot Map for U.S.

Early August's general weather pattern was somewhat typical of summer, with the jet stream and associated storm track displaced to the northern U.S., and high pressure dominating the southern tier of states. However, on several occasions during the month, this pattern broke down, as cooler air advanced southward into the Plains and Midwest. The associated upper-level trough persisted for much of the month. The Ohio Valley received the most substantial precipitation from the combination of frontal boundaries and abundant available moisture. This region's wetness continued a trend that had developed early in the summer. In contrast to the early summer months, August's significant precipitation expanded northward into the Upper Midwest, helping to abate intense drought in the western Great Lakes region. In the south, precipitation was spottier, as is typical of summer. Late in the month, the cool-air incursions reinforced each other, bringing rains further south and east, along the Atlantic coast. However, the late-month precipitation was not vast enough to stop the development of drought and dryness in the southern Atlantic states. In the Southwest, the monsoon feature was weaker than average, and this was largely responsible for the introduction of drought in Arizona.

By the end of August, core drought areas in the U.S. included:

  • South Central Texas, where widespread extreme to exceptional drought remained entrenched;
  • The western and southwestern U.S., notably:
    • most of California and western Nevada, where moderate to severe drought persisted;
    • western Oregon and western Washington, where moderate to severe drought emerged;
    • much of Arizona, where moderate drought emerged;
  • Hawaii, where moderate to severe drought continued across the central and eastern islands;
  • the western Great Lakes, where moderate to severe drought improved somewhat in Wisconsin and Minnesota.

Improvements to smaller drought areas occurred in western Oklahoma, southeastern Alaska, and Montana.

U.S. Pasture and Range Conditions

Reported topsoil conditions indicated typical summer dryness in parts of the United States, but few agricultural areas reported topsoil moisture deficits less than the long-term summer averages. According to observations from the US Dept. of Agriculture (USDA), four states (Texas, New Mexico, Oregon and Washington) reported that more than half of agricultural topsoil was in "Very Dry" condition. However, of these, only the New Mexico and Washington values were above the long-term average. It should be noted that California, Arizona and Nevada, where drought is pervasive, are not accounted for on these maps. In fact, California and Arizona reported a a large percentage of pasture and range land in poor or very poor condition. This rangeland dryness, relative to normal, stretched along the nation's southern border.

U.S. Streamflow Conditions

Streamflow conditions reported by the US Geological Survey (USGS) were largely consistent with other drought indicators east of the Rockies. Texas gauges were near historic lows for the season, while low flows spread up the southern Atlantic states and dominated Arizona and the coastal weatersheds of the Pacific Northwest. Deficits in northern Georgia were striking. Hawaiian streamflow levels were also quite low in most locations.

Five states (Arizona, Colorado, New Mexico, Texas, and Utah) observed August precipitation among the ten driest of the instrumental record (1895-2009), while no states placed among their ten wettest August values of the same period.

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State/Regional/National Moisture Status
A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

States
alabama arizona arkansas california colorado connecticut
delaware florida georgia idaho illinois indiana
iowa kansas kentucky louisiana maine maryland
massachusetts michigan minnesota mississippi missouri montana
nebraska nevada new hampshire new jersey new mexico new york
north carolina north dakota ohio oklahoma oregon pennsylvania
rhode island south carolina south dakota tennessee texas utah
vermont virginia washington west virginia wisconsin wyoming

Regional
northeast u. s. east north central u. s. central u. s.
southeast u. s. west north central u. s. south u. s.
southwest u. s. northwest u. s. west u. s.

National
Contiguous United States

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Drought Indicators
The following indicators illustrate the drought conditions this month:

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Contacts & Questions
For additional, or more localized, drought information, please visit:

Citing This Report

NOAA National Climatic Data Center, State of the Climate: Drought for August 2009, published online September 2009, retrieved on September 2, 2014 from http://www.ncdc.noaa.gov/sotc/drought/2009/8.