September 24, 2010

After this week’s storm system moves east of Nebraska, extended weather models indicate a precipitation free period from September 26 to October 8, with temperatures averaging well above normal.

Weather trends across the U.S. are beginning to resemble conditions normally seen during a La Nina event. Upper air troughs are moving into the Pacific Northwest, digging into the northern and central Rockies, before moving northeast toward the upper Great Lakes.

Temperature swings between much above and much below normal are becoming more frequent over the northern third of the U.S. Frost and/or freeze conditions could easily materialize across the northern Corn Belt within the next few weeks if this trend continues. Fortunately, most agricultural crops are well advanced, with much of the U.S. corn crop already mature or within two weeks of maturity. Northern and western Nebraska, South Dakota, North Dakota, and Minnesota may need up to three additional weeks of normal temperatures to insure that the entire corn crop will be safe from freeze damage.

The corn harvest is underway across the eastern Corn Belt, with limited activity across the western Corn Belt. Corn maturity is running two to four weeks ahead of last year and about a week ahead of the five-year average. After this week’s storm system moves east of Nebraska, extended weather models don't shown any precipitation from Sept. 26 to Oct. 8, with temperatures averaging well above normal.

Currently models for the medium range forecast end Oct. 8. They indicate that the upper air ridge will continue to be centered over the central U.S., which suggests that the dry pattern will continue well past the first full week of October. The resulting air mass will likely bring low relative humidity levels and provide producers with excellent grain dry down conditions. However, the fire risk across rangeland will increase dramatically. This dry stretch could also present problems for winter wheat establishment in the western third of Nebraska.

The Climate Prediction Center fall forecast favors above normal temperatures for October to December from the southern Plains northeastward through the Great Lakes region. Above normal temperatures are expected through mid-November for much of the country (Figures 1 and 2).

Unfortunately, there is a price to pay for this pattern. Significant snow/blizzard conditions have developed abruptly anywhere from late October into early December when a strong upper air trough moves into the Pacific Northwest and collides with the upper air high pressure system typically situated over the southeastern U.S. Most of these events are quickly followed by a warming trend that removes much of snow pack.

See Winter Forecast

Also

• La Nina Effect
• Spring Forecast 2011