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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,
June was drier than normal in a broad swath from the Southwest and southern Plains to the Great Lakes, then eastward to the mid-Atlantic and Northeast states. Parts of this swath have been drier than normal for the last four months (March, April, May, June). For the Pacific Northwest as a whole, June was the fourth near to wetter-than-normal month following a dry winter, although parts of the region were drier than normal this month.
The June precipitation pattern at the primary stations in Alaska was mixed but mostly drier than average along the coast and wetter than average at the interior stations. Across Hawaii, most of the stations were drier than average. In Puerto Rico, the precipitation signal was mixed, based on National Weather Service radar estimates of precipitation. June streamflow averaged near normal for Puerto Rico and the Hawaiian Islands.
Long-term moisture deficits persisted in many areas. Six-month dryness was evident for parts of the Northwest, northern Rockies, southern Plains, Mississippi to Ohio valleys, Great Lakes, and mid-Atlantic states. The Pacific Northwest has experienced a dry winter followed by a wet spring, although spring excesses did not significantly ease six to seven years of precipitation deficits. The southwestern U.S. has been 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 end of June to beginning of July U.S. Drought Monitor maps. 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.
The southwestern U.S. has been 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 end of June to beginning of July U.S. Drought Monitor maps. 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:
June 2005 Drought Pre-Instrumental Perspective
Bighorn Basin, Wyoming and Montana
Despite near-average precipitation over the past 12 months, Wyoming and Montana have been mired in long-term drought since mid-1999. The Bighorn Basin in north-central Wyoming and extreme south-central Montana is representative of conditions in both states, with precipitation in the corresponding climate division (Wyoming Division 4) since July 2000 totaling 84% of the 60-month normal (based on 1950-2000) (also see graph to left).
The graph to the right (annual values in light blue, 5-year weighted average in dark blue) shows the average annual (July-June) precipitation, 1896-2005, for Wyoming Division 4. Several severe multi-year drought events can be seen in this record: around 1900; the mid-1930s Dust Bowl; the 1950s; and the last six years (2000-2005), all of which have been below the long-term average.
Also shown on this graph is a 739-year tree-ring reconstruction (1260-1998) of Bighorn Basin annual precipitation (annual values in light red; 5-year smoothed values in dark red), developed by Gray et al. (2004). This reconstruction is based on four long tree-ring chronologies (one Douglas-fir, three limber pine) from the Bighorn Basin, and was calibrated on an instrumental precipitation record (1907-1996) averaged from five long-term weather stations in the Bighorn Basin, four of which are within Wyoming Division 4: Buffalo Bill Dam, WY; Lovell, WY; Powell Field Station, WY; Worland, WY; and Bridger, MT. The reconstruction was calibrated on a 13-month "annual" period (June-June), but it correlates well with the Wyoming Division 4 annual (July-June) precipitation. Over their common period (1896-1996) the correlation is 0.602, indicating a high degree of shared variance. The precipitation units shown are standardized for comparison; negative values indicate below-average precipitation, and positive values indicate above-average precipitation.
The tree-ring reconstruction can put the precipitation variability of the last century in north-central Wyoming into a much longer perspective. First, the most severe single-year droughts of the 20th century (e.g., 1934, 1956) were probably matched or exceeded on numerous occasions in the previous 650 years. The reconstruction also shows several extended dry periods much longer than those in the instrumental record, including events in the late 1200s and the late 1500s. The latter event has been found, from other tree-ring reconstructions, to have extended through much of North America (Stahle et al. 2000). These events, were they to recur, would likely pose a greater challenge to human activities and ecosystems in the Bighorn Basin than even the severe droughts of the 1930s, 1950s, and 2000-2005.
Resources:
References:
For questions on technical or scientific content of this report, please contact:
Richard Heim:For general climate monitoring questions, please contact:
CMB.Contact@noaa.govFor climate data orders, please contact the National Climatic Data Center's Climate Services and Monitoring Division:
NCDC.Orders@noaa.gov
http://lwf.ncdc.noaa.gov/sotc/index.php
