Tools used in the U.S. Monthly Drought Outlook (MDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for September, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range outlooks, the Week 3-4 outlooks, dynamical models at weekly and monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology, and initial conditions such as soil moisture. The U.S. Drought Monitor, valid on August 24 at 12Z, was used for the initial drought conditions.

Drought conditions continue to blanket the Western Region, with nearly 95 percent of these states experiencing moderate drought conditions (D1) or worse, and more than 60 percent of the region in severe to exceptional drought. While drought conditions gradually continued to worsen across the northwestern CONUS during August, monsoonal convection and below-average temperatures helped to stave off degradations across the Four Corners and Great Basin regions, with some modest improvements noted across Arizona and New Mexico. During early September, another surge of monsoonal convection is expected across the Four Corners. In fact, the National Weather Service currently has flash flood watches issued for all of Arizona, the southern California deserts, western New Mexico, and southern Utah. The enhanced monsoon signal is reflected in the updated CPC monthly outlook for September, with enhanced chances for above-median precipitation extending across much of southern Arizona and New Mexico. Based on these outlooks, additional drought improvements are favored for southern Arizona and New Mexico. Persistence is maintained for the Great Basin, Utah, and northern Arizona and New Mexico, where convection is anticipated to be spottier in nature. Elsewhere across the West, persistence is strongly favored, with enhanced chances for above-normal temperatures during September and below-normal precipitation favored for the Northwest. 

For the Western Region, forecast confidence is high for the Pacific coast states and Montana, and moderate for the Southwest monsoon regions.

Across the High Plains region, drought is also prevalent, with almost 63 percent of the region currently experiencing moderate drought conditions or worse. Drought gradually expanded across the central and northern Plains during August with inadequate precipitation and hot temperatures, but heavy rainfall overspread parts of the eastern Dakotas and northeastern Nebraska at the end of the month. During early September, another round of heavy rainfall is forecast across the eastern Dakotas, eastern Nebraska, and eastern Kansas. This additional rainfall will likely engender drought improvements across the eastern Dakotas and northeastern Nebraska. Although the Week-2 pattern looks drier, temperatures near to below-normal are favored, which should help to avoid quick evapotranspirative loss. In contrast, warm, dry conditions are favored for much of Kansas during the start of the month, which favors persistence of existing drought areas and further drought expansion into areas that are already abnormally dry.

Forecast confidence is low to moderate for the High Plains Region.

Recent rainfall was also heavy across the drought areas of Minnesota and northern Iowa, and the 7-day QPF from WPC shows additional heavy rainfall across the region. Periods of below-average temperatures are likely, and climatological precipitation remains fairly high across the remainder of the Midwest. Therefore, drought improvements are also favored for the entire Midwest Region, with confidence highest across the core drought areas of Minnesota and Iowa. Despite these short term improvements, drought conditions remain deeply entrenched across Minnesota and Iowa, and large areas of moderate to severe drought will likely remain as we go into mid-Autumn.

Forecast confidence is moderate to high for the Midwest Region.

The Southern Region was largely drought free at the end of August, with just under 6 percent of the region experiencing drought conditions. Dry conditions were on the increase across parts of Oklahoma and northern Texas, however, with rainfall deficits running 5 to 75 percent of normal over the last 30 days. During early September, dry, hot conditions are favored to continue, which may prompt some late season flash drought developments where conditions are already abnormally dry. The revised September outlook from CPC maintains equal chances for both temperature and precipitation across most of the region, with above-normal rainfall favored for the Texas Gulf Coast. Therefore, while pockets of drought development are likely to occur, widespread rapid drought development is not likely.

Forecast confidence is low to moderate for the Southern Region.

Across the Southeast Region, only a small patch of moderate drought remains across the central Appalachians of Virginia. Widepsread heavy rainfall associated with the remnants of Hurricane Ida will overspread the Appalachians on September 1st, likely removing this sole area of drought. No other drought is favored to develop across the region during September, where conditions are generally quite wet.

Forecast confidence is high for the Southeast Region.

Adjacent to the drought area in Virginia, a small area of drought remains in West Virginia, and the remnants of Hurricane Ida will likely remove this lingering drought. Wet conditions, including some moisture from Tropical Storm Henri, alleviated drought across most of the Northeast, though some drought remains entrenched across far northern New England. When the September - November seasonal drought outlook was released earlier in August, persistence was maintained for this northern New England drought area in the absence of a clear wet signal. While equal chances were maintained in the updated monthly outlook across far northern New England with the remnants of Hurricane Ida passing south of the region, there is a wet signal present during the Days 8-11 period. This potential wetness, combined with a cooler start to the month, makes further erosion of this drought increasingly likely. Therefore, the persistence was changed to improvement and removal of moderate drought for this monthly outlook.

For the Northeast Region, forecast confidence is high for West Virginia, and low for northern New England.

Improved moisture corresponded to removal of all remaining drought areas across Alaska during August, and with rapidly decreasing temperatures and daylight during September, no additional drought development is favored. Drought persistence is favored for Hawaii, with most models showing near to below-normal precipitation in a climatologically dry time of year. No additional development is favored due to the lack of a clear and strong dry signal. Across Puerto Rico, small drought areas remain on the southern portion of the island, and with the peak of hurricane season rapidly approaching and broad-scale conditions favoring enhanced activity, drought removal was indicated on this outlook.

Forecast confidence is high for Alaska, moderate to high for Hawaii, and moderate to high for Puerto Rico.

Forecaster: Adam Allgood
 
Next Monthly Drought Outlook issued: September 30, 2021 at 3pm EDT