Drought - July 2009
Contents Of This Report:
National Drought Overview
Detailed Drought Discussion
During July, drought's overall extent across the United States held fairly constant. This stopped a months-long trend of a shrinking D1 or greater (D1+) drought footprint. By July 28th, D1+ drought covered 13.8 percent of the contiguous United States, up slightly from June 30th's 13.4 percent. This area is quite small compared to the decade-long record of the U.S. Drought Monitor. However, in many drought-stricken areas, conditions worsened. Coverage of the most significant drought categories (D2, D3, D4) expanded during the month.
The Nation's most significant drought episodes intensified or expanded during July. Exceptional (D4) drought expanded across Central and South Central Texas, where historic and near-historic drought have plagued agriculture and water supplies for months. Generally, conditions in the drought regions surrounding the most intense Texas drought improved: monsoon rains brought relief to southeastern New Mexico, while summer storms helped much of the Mississippi Delta region. Drought remained pervasive in Hawaii, where two-thirds of the state experienced D1+ drought throughout July. In eastern Hawaii, the worst areas of drought intensified, while areas along the edges improved slightly. As in the Texas episode, this resulted in a tightening of the drought's focus on severely drought-stricken areas. In the West, drought affecting nearly all of California and much of western Nevada persisted, with some early-July deterioration along these states' northern border. Severe (D2) drought expanded across the northern half of Wisconsin. Statewide rainfall totals there were the seventh driest on record for July, while the three-month (May-July) values were the sixth driest.
July was dominated by unusually strong and unusually persistent upper-air features over North America. A large trough, centered generally between the Great Lakes and Hudson Bay, remained entrenched for all but a few days during the month. An upper-air ridge prevailed over the Southern Plains. The surface boundaries associated with these features focused rainy areas generally from North Texas northeastward into the Ohio Valley and further into the Northeast. Cool, dry weather prevailed in the Upper Midwest, sustaining the aforementioned Wisconsin drought conditions. During the last half of the month, a persistent ridge feature prevailed across much of the West, resulting in record high temperatures along the West Coast, and Alaska's second-warmest July on record.
By the end of July, core drought areas in the U.S. included:
- the south-central U.S., with substantial D2+ coverage, especially south central Texas, where widespread extreme to exceptional drought remained entrenched, and detached pockets of western Oklahoma and Southern Louisiana.
- portions of the northwestern Great Lakes/Upper Mississippi Valley, especially northern Wisconsin and southern Minnesota;
- parts of the West and coastal Alaska in moderate drought, plus large areas of severe drought in Nevada and California;
- Hawaii, where moderate to severe drought continued across the central and eastern islands;
- portions of the Nation's western border with Canada, where pockets of moderate and severe drought persisted or developed.
Most drought improvements during July were minor, and tended to be along the edges of these core areas.
Streamflow conditions reported by the U.S. Geological Survey were largely consistent with other drought indicators east of the Rockies. Runoff was abundant in the Ohio Valley and Central Mississippi Valleys, while streamflow gauges in southern Texas and northern Wisconsin were near historic lows for the season. The impact of the dry July was evident across the south by late month, where streamflow deficits plagued northern Georgia and much of the surrounding southern Appalachians.
Three states (Delaware: 3rd; Wisconsin: 7th; Georgia: 10th) observed July precipitation among the ten driest July values of the instrumental record (1895-2009). Notably, June 2009 was the sixth driest June of the instrumental record for Georgia. On the wet extreme, each of the six most northeastern states recorded a July among its ten wettest (Massachusetts and Rhode Island: 2nd; Maine: 5th; Connecticut, New Hampshire, Vermont: 6th), and July was the third-wettest on record for Arkansas.
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.):
|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.|
|Contiguous United States|
- Palmer Drought Indices
- Standardized Precipitation Index
- long-term (36 to 60 month) percent of normal precipitation maps
- airport station percent of normal precipitation maps
- statewide precipitation rank maps
- Cooperative station percent of normal precipitation maps
- percent of average maps for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center
- satellite-based observations of vegetative health
- National Weather Service model calculations of soil moisture, runoff, and evaporation
- National Weather Service model calculations of soil moisture using the Leaky Bucket Model
- Midwest Regional Climate Center model calculations of soil moisture
- topsoil moisture conditions observed by the USDA and mapped by the Climate Prediction Center
- pasture and range land conditions observed by the USDA and mapped by the Climate Prediction Center
- streamflow maps maintained by the USGS
Contacts & Questions