Corn crop withered from drought, August 2012, New Florence, Mo. | © Kevin G. Hall | MCT via Getty Images

Corn crop withered from drought, August 2012, New Florence, Mo. (© Kevin G. Hall/MCT via Getty Images)

The setup
The drought and heat had their origins during the prior winter.

A fast storm track over northern Canada during the winter of 2011-2012 prevented cold air from making many visits into the U.S. and kept the frigid air locked up near the Arctic Circle.

According to Expert Senior Meteorologist Brett Anderson, "This pattern, in turn, resulted in mild Pacific air over much of the U.S. and southern Canada. Additionally, a lack of snow cover over southern Canada then allowed any air coming southward to further warm up before entering the U.S."

The lack of cold air in the U.S. then greatly limited the intensity of storms during the winter and influenced the form of precipitation.

Many stream and river systems are fed by the melting of snow cover and the release of frozen water in the ground through the spring and early summer.

Drought begins, heat blossoms
The warm start to the spring allowed some crops to be planted early in the Midwest. However, the soil also dried out very quickly.

As the days lengthened and the angle of the sun increased, temperatures climbed much higher than average over the Midwest and occasionally spread into the East as a result of the dry landscape. Many cities over the middle of the nation had weeks of 100-degree temperatures.

The quick warmup is why also severe weather season spiked very early and was extremely brief.

According to Agricultural Weather Expert Dale Mohler, "We had a lack of large complexes of thunderstorms during the spring and summer over the Plains and Midwest."

Crops shrivel
The thunderstorm complexes are a major source of rainfall during the spring and summer.

Mohler stated that corn was the hardest hit major crop during the drought and even though a record number of acres was planted the number of bushels per acre was down about 25 percent from what was originally anticipated.

"The heat and drought hit much of the corn belt during the critical pollination period for the crop." Mohler stated.

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Soybeans were not hit as hard. This crop takes much longer to mature, and some rain came the rescue late in the period. However, yields were about 12 percent lower than originally expected.

Last year's winter wheat fared better. The wheat, which matured during the beginning of the summer of 2012, had only a minor negative impact due to the drought.

Streams dry up, rivers shrink
The excessive heat and drought not only resulted in reduced crop yields and brown pasture lands, but it also forced water restrictions in some communities.

Levels on the Mississippi River, which was near record high levels only a year earlier, plunged to 50-year lows during the summer of 2012.

These levels continued to dip during the autumn as the lack of storms with heavy precipitation continued.

During the summer and autumn, levels became so low that drudging operations on behalf of the Army Corps of Engineers were stepped up to keep the shipping channel open. However, barge companies were still forced to lighten their loads to avoid running aground.

Concerns continue for possible closures along the waterway into this winter above where the Ohio River joins in. Most notably affecting the port of St. Louis.

According to AccuWeather.com's Long Range Team of meteorologists, headed by Paul Pastelok, "During this winter, rain and snow is projected to be adequate over the Ohio Basin but still may be low enough over the upper Mississippi River for concern with low water levels. Little rain and snow is projected over much of the Missouri Basin and other areas farther south over the Plains."

It will take more than one or two storms like that of the middle of December over the Plains and Upper Midwest to substantially turn things around over the upper Mississippi and Missouri valleys.

Drought and heat extremes
For some areas of the Central states, this year will finish high on the list of driest years on record. It isn't so much individual cities that have record dryness, but more the number of locations that were abnormally dry throughout the nation. Only the Northwest and portions of the northern Gulf Coast were regions where rainfall was significantly above normal over a broad area.

Following the warmest first six months of the year and the hottest summer on record across the lower 48 states, it soon became apparent that 2012 in its entirety would be in the running for the hottest years on record.

According to Steven A. Root, President and CEO of WeatherBank, Inc., "2012 is set to be the warmest year on record in the United States and southern Canada since 1950."

Not even cooler conditions during November took 2012 out of the top spot. Unusual warmth returned during the first part of December. Virtually every reporting site in the lower 48 states had temperatures averaging above normal during the first 20 days of the month.