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Climate Prediction Center


August-October 2005


Latest Seasonal Assessment - Lingering moderate to severe (D1-D2) hydrologic drought is expected to persist across much of Washington, Oregon, Idaho, Wyoming and western Montana. Late summer and early fall are generally not the best times of the year for the significant, widespread precipitation needed to ease long term drought. In the Southwest, a late start to the monsoon will result in a shortened wet season. In areas dependant on the monsoon for the majority of the annual rainfall total, this may trigger moderate drought. Soaking rains from Hurricane Emily will result in drought improvement across deep southern Texas, while some improvement is anticipated across eastern Texas, southeastern Oklahoma and the lower Mississippi Valley. Improvement is expected across the Great Lakes as the pattern becomes more favorable for precipitation and eventually cooler temperatures. Some improvement in the severe to extreme drought (D2-D3) is expected over northern Illinois.

Discussion for the Seasonal Drought Outlook

Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for August-October, the drought termination and amelioration probabilities for October, various medium and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, the soil moisture tools based on the GFS model and the Constructed Analogues for the season, and the latest western water supply forecasts.

A wet spring has resulted in long term drought improvement over most of the Great Basin, northern Rockies and northern High Plains. However, the wet spring came on the heels of several years of below normal precipitation and anomalously warm temperatures which plagued much of Idaho, Montana and Wyoming. Snowfall during the preceding winter was below to much below normal in the Bitterroot, Absaroka and Salmon River Mountains. As a result, moderate to severe (D1-D2) long term drought continues across the region. Further west, the wet spring was preceded by a very dry winter. Record and near record low snowpacks were observed across Oregon and Washington. Despite the much needed moisture from abundant spring precipitation, the deficits incurred during the winter were too large to be overcome by the wet spring. As a result, moderate to severe drought continues over large portions of these states. Because the months of August, September and October are relatively dry in the northern Great Basin and northern Rockies, the long term drought will persist in these areas. The next chance for improvement will come in the autumn and winter when Pacific storm systems once again produce rain and mountain snow across the region. In the northern High Plains and Black Hills, late summer showers and thunderstorms may result in some improvement. However, long term drought will likely persist through the period. The best chance for improvement will come in spring, when melt water from the mountains to the west recharge area rivers and spring precipitation falls on the Plains.

In the southwestern U.S., abundant rain and snow so far this water year has resulted in precipitation amounts that are 100 to 200 percent of normal in much of eastern Arizona and western New Mexico. However, pockets of moderate (D1) long term drought persist due to drought in previous years and localized areas of lighter precipitation. Lingering drought will continue during the period in these pockets. The monsoon is quite late in arriving to the Southwest. In Tucson, Arizona, the monsoon started on July 18. This is the second latest start since 1949. The monsoon was preceded by 35 consecutive days with 100+ degree heat. Other years that have seen a very late start to the monsoon were 1997, 1987 and 1979. In these years, rainfall was 70 to 90 percent of normal for the period June-September. Therefore, there is a greater than average probability that rainfall will be below average for June-September 2005. This is consistent with the CPC seasonal forecast for August-October 2005. However, the deficits incurred should not be sufficient to initiate severe drought in the area. Nevertheless, the short falls could be enough to trigger moderate drought in areas of Arizona and New Mexico which typically net the majority of their annual precipitation during the late summer. Therefore, possible drought development has been indicated in eastern Arizona, southern New Mexico and adjacent parts of far western Texas.

Soaking rains from Hurricane Emily will result in drought improvement across the southern most counties of Texas. As September and October approach, rainfall amounts tend to increase across eastern Texas and southeastern Oklahoma, as well as the chances for drought improvement. Although drought improvement is possible, there is uncertainty about the late summer and early autumn rains in these areas. Further north, some improvement appears likely across Arkansas, Missouri and Illinois. However, lingering drought effects may persist. Across the Great Lakes, a more active storm track, increased precipitation and cooler temperatures will ease drought across Michigan, Wisconsin, northern Indiana and northwestern Ohio as fall begins.

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NOAA Center for Weather and Climate Prediction
Climate Prediction Center
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Page Author: Climate Prediction Center Internet Team
Page last modified: December 13, 2006
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