La Niña's influence contributed to cool weather and extensive spring flooding in the Ohio, Mississippi, and Missouri River basins, along with historic heat and drought in the south-central United States. Wet conditions were a detriment to planting in the eastern Corn Belt and the Mid-South, ultimately exposing late-developing summer crops to unfavorable heat and dryness during the heart of the growing season.
However, any Midwestern crop stress was overshadowed by relentless heat and drought on the southern Plains. The drought, which began during the autumn of 2010, devastated the southern Plains' 2011 winter wheat crop and left the region's pastures and rangeland in the worst condition since records of that type have been kept.
Severe crop stress carried through the summer months, sharply reducing yield potential for crops such as cotton and sorghum. Although significant rain and snow finally fell late in the year across the south-central United States, much more precipitation was needed to replenish sub-soil moisture and assist in the long-term recovery of pastures, rangeland, and water supplies.
The West had an erratic, but ultimately abundant, wet season in 2010-2011,with the exception of drought-affected Arizona and New Mexico. In an ironic twist, much of the West experienced an extremely slow start to the 2011-2012 wet season, except for abundant early-season snowfall in the Southwest. By year's end, effects of developing drought were becoming more apparent in California in the form of stunted pasture growth and increased irrigation requirements.
Meanwhile, tornadoes claimed at least 552 lives in 2011, the Nation's highest toll since 1936. Most of the fatal tornadoes struck the central and southern Plains and the Southeast, with Alabama and Missouri hit especially hard during super-outbreaks in April and May. Farther east, the Atlantic Basin was active again with 18 named tropical storms, continuing a general trend of above-normal tropical activity that began in 1995. Only six of the storms became hurricanes, but Irene - the season's first hurricane - struck the middle and northern Atlantic States in late August before triggering catastrophic flooding in parts of New England. Just a few days later, the remnants of Tropical Storm Lee brought additional flooding to the Northeast.
For the Nation as a whole, initial data indicated that the Lower 48 States posted their 23rd-warmest, 45th-driest year during the 117-year period of record. Continuing a long-running stretch of warm years, the Nation's annual average temperature of 53.8 degrees Fahrenheit was 1.0 degree above the long-term mean. The last time the Nation experienced an annual average temperature below the 20th century mean was 1996. Meanwhile, the Nation noted its driest year since 2002, with an annual average precipitation of 28.78 inches (99 percent of normal). State temperature rankings ranged from the 17th-coolest year in Washington to the warmest year on record in Delaware.
In addition, top-ten rankings for warmth covered Texas (second-hottest year, behind only 1921), Oklahoma, Florida, Vermont, and every Atlantic Coast State from North Carolina to Maine. Texas also endured its driest year on record, supplanting 1917. Elsewhere, State rankings ranged from top-ten dryness in Georgia, Louisiana, New Mexico, and South Carolina to the wettest year during the 1895-2011 period of record in Indiana, Kentucky, Massachusetts, New Jersey, New York, Ohio, and Pennsylvania.