A major change in the upper air pattern is still on schedule for later this week into the weekend. The mild beautiful weather of last week is now history over the central US. So far this week a series of upper level troughs have been moving through, each with some rain then some chilly air. These are the front runners of a much larger trough that will form over the center of the country this weekend.
The main outbreak of chilly fall air will occur over the weekend. The graphic shows the ECMWF model forecast at 500mb (~18,000 feet) valid Saturday morning. Notice the flow is coming down from way up in northern Canada. This basic north flow is forecast to continue through all of next week. Even colder air will be spilling into the country Monday night into Tuesday as another upper level system moves through.
For the Chicago metro area, this all translates into the coldest air of the fall season. The highs today, Wednesday, of only the 50s is only the first of many such days. By next Tuesday or Wednesday we will see highs only in the mid to upper 40s. Frost and/or freeze conditions are likely Sunday and Monday morning away from the city core, and pretty definite by next Wednesday morning. The city will most likely escape the first bought of frost, but not the second outbreak by next Wednesday.
Over the northern Plains, cattle ranchers are continuing to add up the cost of the blizzard two weeks ago. Many cattle were still out grazing, so were exposed to the heavy wet clinging snow in the storm. The result has been the loss of tens of thousands of cattle as they froze to death due to the wetness of the snow that clung to their bodies, and then froze in the 70 mph winds. There is one estimate of up to 100,000 cattle lost due to the storms.
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