October - December 2011

Outlook Graphic: GIF   PDF 

Latest Seasonal Assessment - The drought outlook for September 15, 2011 – December 2011 was based primarily upon climate anomalies associated with La Niña as it is expected to strengthen and continue throughout this period. Persistence or development can be expected across much of the Southeast excluding North Carolina and areas soaked by Tropical Storm Lee. The return of La Niña also elevates the chances for persistence across the exceptional drought areas of the southern Plains. It should be noted that forecast confidence across the western Gulf region and Southeast is tempered due to the potential for heavy rainfall associated with tropical cyclone activity during the fall. The waning of the summer monsoon and enhanced odds for below median precipitation during October – December favor persistence or development across most of the Southwest. Based on consecutive La Niña composites, persistence or development is favored across the middle Mississippi Valley and lower Ohio Valley. A slightly drier climatology from October through December tilts the odds towards persistence for the small drought areas in the northwest Corn Belt and upper Mississippi Valley. Across Hawaii, drought persistence is forecast for the western Big Island, Molokai, and Maui since the wet signal associated with La Niña typically becomes established later in the winter.

Tools used in the U.S. Drought Outlook (USDO) included the official CPC temperature and precipitation outlooks for October 2011 and the long lead forecast for October - December 2011, 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 Analogue on Soil (CAS) moisture, the Climate Forecast System (CFS) seasonal precipitation forecasts, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions.

A persistent ridge of high pressure maintained hot and dry conditions across the south-central U.S. into early September, maintaining a large area of extreme to exceptional drought. Texas had its driest summer on record, with a statewide average of 2.44 inches of rain. 2011 was the hottest summer on record for Oklahoma and Texas with average temperatures of 86.5 degrees F and 86.6 degrees F, respectively. According to the National Climatic, Texas recorded the hottest summer for any state. On September 13, Dallas-Fort Worth broke the previous record (69 in 1980) for most 100 degree days in a year. At the beginning of the period, a cold frontal passage is expected to bring 1-2.5 inches of rainfall to southeast Kansas and northeast Oklahoma where some improvement is forecast. Across the remainder of the southern Plains, tools on all time scales and consecutive La Niña composites indicate enhanced odds for below median precipitation. Therefore, persistence is forecast for much of Oklahoma and Texas. However, forecast confidence is tempered by the potential for tropical cyclone activity through the end of November that could provide relief to the western Gulf region.
Forecast confidence for the southern Plains is moderate.

During the summer, monsoon rainfall provided some drought relief to eastern Arizona and western New Mexico. Locally heavy rainfall and flash flooding occurred in the desert Southwest during early-to-mid September. Therefore, development that was forecast in the previous outlook across the desert Southwest was removed. The waning of the monsoon coupled with forecasts of enhanced odds for below median rainfall during the upcoming three months favors persistence or development across Arizona, southeast Utah, southwest Colorado, and much of New Mexico. Some improvement is forecast in southeast Colorado and northeast New Mexico due to moderate to heavy rainfall expected at the beginning of the period.
Forecast confidence for the Southwest is moderate.

Across the Southeast, heavy rainfall associated with Tropical Storm Lee eliminated drought and abnormal dryness across southeast Louisiana along with parts of Alabama and Mississippi. Outside of Lee’s track, drought continued in Arkansas, western Louisiana, southeast Alabama, central and southern Georgia, the Carolinas, and parts of Florida. During the remainder of September, an upper-level trough is expected to increase the odds for near to above median rainfall in North Carolina where improvement is forecast. The October-December climatology across south Florida trends much drier, with this region receiving only 10-20 percent of their annual rainfall (versus a normal distribution of 25 percent) during the period. Without heavy rainfall from a tropical system, persistence can be expected for the small drought area at Lake Okeechobee in south Florida. Based upon the seasonal CPC precipitation outlook and consecutive La Niña composites, persistence or development is forecast for the Southeast where heavy rainfall did not occur with Tropical Storm Lee.
Forecast confidence for the Southeast is moderate.

Across the upper/middle Mississippi Valley, lower Ohio Valley, and western Corn Belt, a lack of late summer rainfall resulted in drought expansion. Based upon consecutive La Niña composites, persistence and development is forecast for the middle Mississippi Valley and lower Ohio Valley. To the west and north of this region, signals among tools for October-December are rather weak and the seasonal outlook for OND indicates equal chances for below, near, and above median precipitation. Since the climatology tends slightly drier during this period, odds are tilted towards persistence for the upper Mississippi Valley and western Corn Belt.
Forecast confidence is moderate for the middle Mississippi Valley and lower Ohio Valley and low for the upper Mississippi Valley and western Corn Belt.

In Hawaii, drought continues on the western Big Island, Maui, and Molokai. Although the return of La Niña favors above median precipitation across the Hawaiian Islands, the wet signal typically occurs later during the winter season. Therefore, persistence is forecast at this time for the ongoing drought areas.
Forecast confidence for Hawaii is low.