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Climate Prediction Center

 
 
 

August - October 2006

 

Latest Seasonal Assessment - July heat and dryness rapidly worsened conditions across the northern Plains and upper Midwest, resulting in drought expansion across much of the region. The Outlook indicates that drought should largely continue in this region and also southward into Texas as well. In contrast, the summer monsoon rains are likely to offer short-term relief to the Southwest, Colorado, and southern Wyoming. Relief for water supplies will likely need to wait until next winterís snow season, at the earliest, since snow melt is the major source for water in the West. Some improvement is also expected in Wisconsin, Iowa, and Missouri, as well as the interior South. The best odds for improvement extend along the Gulf Coast from Louisiana to northern Florida and into the southern Appalachians, as well as parts of southern Texas.

 
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 and the soil moisture tools based on the GFS model and the Constructed Analogues for the season.

Hot, dry weather resulted in major drought expansion and intensification across the northern Plains and upper Midwest as anticipated when the Outlook was updated on July 7. Although temperatures should tend to be above normal over parts of the northern Plains during the last half of July, a repeat of the triple digit heat seen during the mid-July heat wave is not forecast. The 90-day temperature outlook indicates a tendency for above-normal temperatures across the central and western states for August-October, with equal chances for wet, dry, and normal across the central United States. Although there is no strong signal for dry weather during August-October in the Plains states, the CAS (Constructed Analogues from Soil moisture) suggests a tendency for dryness to persist from Texas to the Dakotas and Minnesota through the end of October, while the CFS (Climate Forecast System) model leans toward below-normal rainfall in the southern Plains. In short, further drought intensification and expansion may be on hold for the time being in the northern parts of the drought region, but there are also few signs of major relief, so the odds lean toward drought continuation at this time. Both short-term models and the CAS indicate greater odds for improvement in the western Great Lakes region, so some drought improvement is depicted in the Wisconsin area and eastern Iowa into Missouri. In addition, the drought amelioration probability data suggest relatively favorable odds for improvement in Wisconsin. The odds lean slightly toward dryness for August-October in the Michigan-Indiana area, as shown in the new long-lead seasonal precipitation outlook, but short-term moisture conditions seem sufficient to lower the risk for drought development at this time.

The Southwest monsoon appears to be on course for normal to above-normal rainfall this summer, based on the early start of the season, recent heavy rains, the negative correlation with winter dryness, medium-range forecasts, and the August-October regression forecast from the SWcast model produced at the Earth System Research Laboratory. The latter does show a signal for dryness in southwest Arizona, so improvement is cut off for this area. No more than limited improvement is indicated in the region due to the dependency on moisture from winter snowfall for water supplies. This means enduring drought relief will tend to wait until next winter, at the earliest.

The first 2 weeks of the outlook period are expected to see above-normal rainfall across the South, contributing to the improvement depicted in the Drought Outlook. Beyond that period, there is much uncertainty, as the long-lead seasonal rainfall outlook indicates equal chances of wet or dry outside of the Atlantic coast, which has a wet bias. Given the active Gulf of Mexico convection seen in the near-term and the summer rainfall climate, the best odds for improvement appear to extend from Louisiana to Florida. However, rainfall deficits for this year range up to 20 inches from southeastern Louisiana into the Florida Panhandle, so drought eradication will be difficult absent a hurricane or tropical storm, and the path any such storm would take is not known at this time.

The improvement shown for the Georgia to North Carolina area is consistent with short-term forecasts for abundant rains in this area as well as some long-term models, including the CFS. The drought amelioration probability statistics based on historical weather also support drought improvement in Georgia, Florida, and South Carolina.

Elsewhere, Hawaii bears watching, as dry conditions have been affecting the islands. Seasonal rainfall outlooks indicate equal chances of wet or dry, so no drought development is indicated.


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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: July 20, 2006
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