Drought - April 2005
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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 April 2005.
- Moderate to extreme drought affected about 10 percent of the contiguous U.S.
- April was the second wetter-than-normal month across parts of the Pacific Northwest and northern Rockies, following a string of four very dry months.
- The month was drier than normal in the southern Plains and parts of the Great Lakes.
- Long-term moisture deficits (last 24 to 36 to 60 months) persisted across much 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 April 2005, a decrease of about 2 percent compared to last month
- about 10 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of April
- 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 April
- 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).
April was the second wetter than normal month across parts of the Pacific Northwest and northern Rockies, following a string of four very dry months. The month was drier than normal in the southern Plains and parts of the Great Lakes.
The April precipitation pattern at the primary stations in Alaska was mixed and drier than average for Hawaii. In Puerto Rico, most of the island had much above-normal rainfall during April, based on National Weather Service radar estimates of precipitation. This is in contrast to recent moisture shortages across the island. April streamflow averaged near normal for Hawaii and Puerto Rico.
Long-term moisture deficits persisted in many areas. Six-month dryness was evident for parts of the Southeast. The Pacific Northwest experienced its seventh driest November-April on record this year, which is a continuation of dry conditions that started some six to seven years ago.
The southwestern U.S. has been very wet during the winter and early spring though long-term deficits remain across parts of the Southwest, most of the West, and much of the central to northern Plains. These are reflected in the end of April 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:
- Two states (ND, OK) had the tenth driest, or drier, February-April (most recent 3 months) on record.
- Three states (WA, OR, ND) had the tenth driest, or drier, November-April (most recent 6 months) on record.
- End-of-month and monthly averaged soil moisture conditions were drier than normal across parts of the northern Rockies and northern High Plains, the central Plains, the Pacific Northwest, and the coastal Southeast, based on model computations (CPC-1, CPC-2, MRCC). The models also indicated dry soil moisture conditions in eastern Alaska and near the surface and at depth across parts of the central Plains to the Great Lakes.
- Streamflow levels were below seasonal norms across much of the Pacific Northwest and parts of the northern Rockies, northern and central Great Plains, both as computed by models and based on USGS observations.
- The overall circulation pattern during this wet season has resulted in a sharp north-to-south contrast of the snow water content of the western mountain snowpack. Basin-averaged end-of-April snowpacks in parts of Arizona, Nevada, central California and Utah were above average, while snowpacks in Oregon, Washington, Idaho, Montana and the east slopes of the northern Rockies were significantly below average. This pattern is also apparent in basin-averaged water-year-to-date precipitation anomalies. Snowpack conditions in Alaska were generally above normal in the interior regions, below normal in coastal areas.
- Reservoir levels in the West reflected the abundance (Arizona) or lack (many other states) of precipitation, or preventative actions taken by water managers in anticipation of summer shortfalls (Washington). 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 (November, December, January, February, March, April) resulted in an expansion of the western drought area to about 26% by the end of February. Near- to above-normal precipitation from storms during the last several months in the Pacific Northwest brought the western area coverage down to near 20% by the end of April.