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Big weather changes on the way

A large area of high pressure is currently establishing itself over the Plains and Midwest. Temperatures this morning are coldest over the northern and central Plains where a weak surface pressure gradient has allowed temperatures to dip into the teens and 20s. Across the Midwest, morning lows range from the low- to mid-40s across Indiana and Ohio with mid- to upper-30s across most of Illinois and Iowa.

Today strong high pressure and ridging aloft will provide mainly sunny skies across much of the Plains and Midwest. Coldest temperatures this afternoon will reside in northern Minnesota and Wisconsin where some locations will fail to break freezing. Elswhere, 40s and 50s are likely across a good portion of the Plains and Midwest.

Tomorrow this high pressure center shifts east. Expect more in the way of sunny skies and overall fanastic harvest weather across the Plains and Midwest, with temperatures rising into the 40s and 50s for the Midwest and northern Delta, with 50s and 60s across the central Plains as far north as South Dakota. Wednesday some weak upper-level energy will generate clouds and isolated rainshowers across the eastern half of Iowa into Missouri, Illinois, and Minnesota. Rainfall will be light and spotty with 20% coverage of 0.1" rainfall, with some localized pockets of 0.25" possible. Minor impacts to harvesting are expected.

Wednesday night into Thursday an upper trough will dig into the Plains, bringing more organized rainfall across the southern Plains into the Delta. Thursday night into Friday this rainfall will overspread the southern half of the Midwest, with showers continuing into early Friday. Some light snowshowers will be possible Friday afternoon across the central Midwest as an Arctic front pushes through. Rainfall totals across the Plains will generally be in the 0.25 to 0.5" range for southern Nebraska, Kansas, and Oklahoma with 0.5 to 1.0" possible across Missouri, the Delta, and much of Illinois, Indiana, and Ohio.

Colder and drier weather will arrive across much of the central part of the country this weekend. In fact, both the GFS and ECMWF are in agreement for temperature anomalies Saturday and Sunday of 10 or more degrees below average, with the possiblity of much of the Midwest staying near or below freezing Saturday. The worst of the cold will be felt Friday morning across the northern Plains where many areas may fall below zero, likely forcing much of the planted winter wheat into dormancy. Lows near zero are possible as far south as Kansas depending on how far south the Jet Stream is able to travel.

Overall, with favorable harvest weather today through Wednesday, most of the remaining summer crops will likely be harvested. Harvesting delays are likely Thursday and Friday for the southern Plains, central/eastern Midwest, and Delta with a return to drier weather this weekend. The northwest Midwest will likely stay north and west of the action this week with minimal delays expected here.

Looking further down the road, computer models diverege with respect to the longevity of this weekend's cold shot. The ECMWF argues for a return to near-normal temperatures next week while the GFS stays cold due to a more suppressed Jet Stream. Better agreement is found with respect to rainfall where the GFS/ECMWF/CMC all restrict any appreciable rainfall to the Delta and extreme southern Midwest.

Freese-Notis Weather/Weather Trades, Inc. Des Moines, Iowa Copyright 2012 - All Rights Reserved

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