 NCDC / Climate Mon. /
Climate-2007 / Jul / U.S. Drought / Help
Climate of 2007 - July
U.S. Drought Watch
National Climatic Data Center, 15 August 2007
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Global Analysis /
Global Hazards /
United States /
Extremes
Use these links to access detailed analyses of Global and U.S. data.
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Contents Of This Report:
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 National Overview
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- Based on the Palmer Drought Index,
severe to extreme drought affected about 25 percent of the contiguous United States as of the end of July 2007, a decrease of about 2 percent compared to last month.
By contrast, about 15 percent of the contiguous U.S. fell in the severely to extremely wet categories.
- About 38 percent of the contiguous U.S. fell in the
moderate to extreme drought categories (based on the Palmer Drought Index) at the end of July.
- On a broad scale, the previous two decades (1980s and 1990s) were characterized by unusual wetness with short periods of extensive droughts, whereas the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness (
moderate to extreme drought,
severe to extreme drought).
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- A file containing the national monthly percent area severely dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories.
- Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page in files having names that start with "drd964x" and ending with "txt" (without the quotes).
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Detailed Drought Discussion
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Severe to extreme drought expanded across much of the West and into the northern High Plains during July (U.S. Drought Monitor for July 3 vs. July 31). Scattered showers and thunderstorms brought limited short-term relief to some parts of the drought-ravaged Southeast, while dry conditions expanded moderate to severe drought into parts of the Great Lakes and mid-Atlantic regions. By the end of the month, moderate to severe drought generally stretched in an inverted "U" shape from the Southeast through the northern Plains to the Southwest.
In the southeastern anchor of the inverted "U", extreme to exceptional drought was concentrated across much of Alabama, Georgia, and Tennessee. The dryness has been especially acute for the last six to eight months. Statewide, Tennessee had the driest January-July in the 113-year record, with Alabama second driest and Georgia fourth driest. Most of the Southeast states ranked in the top ten driest for year-to-date precipitation.
Excessive heat and drought, combined with low humidities and steady winds, resulted in widespread wildfires this month across much of the West, especially the northern Rockies. The largest wildfire in state history flared up in Utah. Idaho had the second driest March-July and January-July, while Montana ranked ninth driest for June-July. It was the hottest July on record for Idaho, Montana, and Wyoming, and second hottest for Nevada.
About two-thirds of the western U.S. (Rockies westward) fell in the moderate to extreme drought category, and about half fell in the severe to extreme category (as defined by the Palmer Drought Index) by the end of this month.
For July, four states ranked in the top ten driest category, with the most severe dry anomalies concentrated in the northern Plains. South Dakota had the fourth driest July and Minnesota the seventh driest July on record. The remnants of Hurricane Cosme brought heavy rain to eastern parts of the Big Island, but Hawaii had below-normal rainfall across most of the islands this month, continuing a dry trend which has been going on for the last 12 months or longer. The rainfall pattern over Alaska and Puerto Rico was mixed during July.
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The prolonged drought prompted several states to take remedial action. In early July, Gov. Bredesen requested a federal designation of natural disaster for agriculture for all 95 counties in Tennessee to help farmers who have suffered crop and livestock losses as a result of extreme drought conditions. All 67 counties in Alabama were designated by the USDA in July as natural disaster areas due to drought. Near the end of the month, Gov. O'Malley asked the USDA for a Secretarial Disaster Designation for those Maryland counties impacted by dry weather and excessive heat in June and July.
Hundreds of daily maximum temperature records fell across the West during the month. The record and near-record heat in the northern Rockies and northern High Plains magnified evaporation, which exacerbated the drought conditions. Pocatello, Idaho reported the warmest July on record, as did Missoula, Kalispell, and Butte in Montana. Other temperature records: Missoula recorded a new all-time record high of 107 °F and had 11 days with highs of 100 °F or greater during July, shattering its 1936 annual record of 6 days. Bozeman, Montana set a new all-time record high temperature several times during July, exceeding the 1941-2006 record of 103 °F six times. Miles City, in eastern Montana, reported 110 °F on July 23, which tied its second-hottest day on record behind 113 °F on July 18, 2003.
The drought and heat wave ravaged pastures and rangeland from the Southeast to the Great Lakes, and across much of the West. Two-thirds or more of the pasture and rangeland was rated poor or very poor in Maryland, Michigan, Minnesota, Nevada, and Virginia, with up to 97 percent in California. Soils (both observed and modeled) dried out, rivers and streams (both observed and modeled) shrank, and vegetation was stressed.
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State/Regional/National Moisture Status
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Pre-Instrumental Perspective
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There is no July 2007 Paleoclimatic Perspective.
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Drought Indicators
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The following indicators illustrate the drought conditions this month:
- 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
- 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.
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Additional Contacts:
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- For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:
Climate Services Division
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4876
phone: 828-271-4800
email: ncdc.info@noaa.gov
- For further information on the historical climate perspective presented in this report, contact:
Richard Heim
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Richard.Heim@noaa.gov
-or-
Jay Lawrimore
NOAA/National Climatic Data Center
151 Patton Avenue
Asheville, NC 28801-5001
fax: 828-271-4328
email: Jay.Lawrimore@noaa.gov
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NCDC / Climate Mon. /
Climate-2007 / Jul / U.S. Drought / Help
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