U.S. Drought Highlights:
- On the national scale, severe to extreme drought affected about 6 percent of the contiguous United States as of the end of July 2005.
- Moderate to extreme drought affected about 15 percent of the contiguous U.S.
- The month was drier than normal across much of the West, especially the Pacific Northwest and Rocky Mountain states, and parts of the Great Plains.
- Below normal precipitation fell across parts of the Mississippi and Ohio River valleys, Great Lakes, and into the Northeast. Dry weather has dominated much of this area, into the southern Plains, since March.
- Long-term moisture deficits (last 24 to 36 to 60 months) persisted across parts of the West into the northern High Plains and central Plains.
Please Note: The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed.
On the national scale,
- severe to extreme drought affected about 6 percent of the contiguous United States as of the end of July 2005, an increase of about 2 percent compared to last month
- about 15 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
- about 22 percent of the contiguous U.S. fell in the severely to extremely wet categories at the end of July
- a file containing the national monthly percent area severely dry and wet from 1900 to present is available
- 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).
July was drier than normal across much of the West, especially the Pacific Northwest and Rocky Mountain states, and parts of the Great Plains. Below normal precipitation fell across parts of the Mississippi and Ohio River valleys, Great Lakes, and into the Northeast.
The July precipitation pattern at the primary stations in Alaska was mixed but generally drier than average in the west and wetter than average in the east. Across Hawaii, most of the stations were drier than average, especially in Kauai and the Big Island for July and the last 3 months. In Puerto Rico, the precipitation signal was mostly wetter than normal, based on National Weather Service radar estimates of precipitation and 4-week station reports. July streamflow averaged near normal for the Hawaiian Islands and wetter than normal for Puerto Rico.
Long-term moisture deficits persisted in some areas. Dry weather has dominated much of the region from the southern Plains, across the Mississippi and Ohio River valleys, into the Great Lakes and Northeast, since March (March, April, May, June, July). The northern Rockies and Pacific Northwest exhibit a dry signal from 9 months out to 60 months, reflecting the severe drought which has plagued the region for most of the last 6 years.
A late start to the monsoon season resulted in a dry July across parts of the Southwest. This region was very wet during the winter and spring, although long-term deficits remained across parts of the Southwest and West, and much of the central to northern Plains. This is reflected in the early August U.S. Drought Monitor map. The Southwest has recovered at the 12 to 24 month timescales, but still shows dryness in some parts at the 36 to 60 month timescales.
Some regional highlights:
- Four states had the tenth driest, or drier, July in the 111-year record.
- New Mexico had the second driest June-July.
- Three states had the tenth driest, or drier, May-July on record.
- Two states (Arkansas and Illinois) had the tenth driest, or drier, April-July.
- Three states (Arkansas, Illinois, Missouri) had the tenth driest, or drier, March-July.
- Two states had the tenth driest, or drier, February-July on record.
- Arkansas had the tenth driest December-July.
- By the middle of the month, more than half (59%) of Wisconsin's pasture and range land was in poor to very poor condition. On July 15, Wisconsin Governor Jim Doyle declared a statewide drought emergency to expedite irrigation relief for farmers (Wisconsin Ag Connection, 07/18).
- By the end of the month, 60% of the pasture and range land was in poor to very poor condition in Arizona (61%) and Arkansas (60%), with three-fourths in Missouri (78%) and Illinois (74%). In response to a request by Illinois Governor Rod Blagojevich, U.S. Department of Agriculture Secretary Mike Johanns designated nearly all of Illinois' counties drought disaster areas (Brownfield Network, 7/27). Burn bans were in effect in several Arkansas counties (NWS, 7/21).
- End-of-month and month-averaged soil moisture conditions were drier than normal across a broad swath from the southern Plains to the western Great Lakes, and parts of the Pacific Northwest, northern and central Rockies, Ohio Valley, and Northeast, based on model computations (CPC-1, CPC-2, MRCC). The models also indicated dry soil moisture conditions in east central and southeastern Alaska, parts of Hawaii, and near the surface and at depth from the western Great Lakes to Ohio Valley.
- According to end-of-July USDA observations, more than 50 percent of the topsoil moisture was rated short to very short (dry to very dry) in most of the Pacific Northwest, Rocky Mountain, and Great Plains states, spreading into the Ohio Valley and western Great Lakes. This is drier than the 5-year and 10-year averages across much of the area.
- Streamflow levels were below seasonal norms across parts of the Pacific Northwest, Rocky Mountain states, central Plains, Great Lakes, Mississippi and Ohio valleys, both as computed by models and based on USGS observations.
- Several large wildfires burned across the West during the month. By mid-July, most of the fires were concentrated in the Southwest, where unusually heavy precipitation during late fall to spring resulted in rapid and extensive undergrowth which provides abundant fuel for the fires. The dry July weather was exacerbated by unusually hot temperatures. By early August, many of the Southwest fires had abated, but several new fires had started in Alaska and the Pacific Northwest.
- Reservoir levels in the West reflected the long-term precipitation deficits in many states. The percent area of the western U.S. (Rockies westward) experiencing moderate to extreme drought (as defined by the Palmer Drought Index) decreased from about 67% in July 2004 to under 10% by October. Intensification of drought in the Pacific Northwest during winter and early spring (Nov., Dec., Jan., Feb., Mar., Apr.) resulted in an expansion of the western drought area to about 28% by the end of February. Above-normal precipitation from storms during late spring to early summer in the Pacific Northwest brought the western area coverage down to near 11% by the end of June. A dry July increased the western drought area to about 17%.