The autumn that can't make up its mind.
The first 12 days of September averaged 4.7 degrees Fahrenheit below normal. Then, the pattern shifted dramatically, and the next 41 (that's f o r t y o n e) days (from September 13 through October 23) averaged 9.9 degrees Fahrenheit above normal - and not a single one of those 41 days was below average. Not one. It was warm. Very warm. Saturday, October 21 saw a high temperature of 77 and a low temperature of 60. That's approximately the daily range of temperatures you'd expect to see on September 5, for example.
And then, shit hit the fan. Late autumn came on strong, and the week since October 23 has averaged 5.9 degrees Fahrenheit below normal. This is all depicted in the following graph:
Today, Halloween, for example, reached a high of only 40 degrees as O'Hare airport, making this the 10th coldest Halloween since 1872.
One more chilly night
One more chilly night may be in the offing tonight, with temperatures just sneaking down close to freezing, before another pattern shift may alter our weather once again.
A big warmup could be in store this weekend, where temperatures may sneak back up to 70 degrees on Sunday. But first, the deep trough that has plagued our weather for the past week has been replaced by more zonal flow, as evidenced by these contrasting plots showing the upper air patter (blue = cold, red = warm) for Saturday, October 28 and Sunday, November 5:
This means that temperatures will begin to moderate tomorrow, with highs on Wednesday reaching 50 or above.
But it also means that more active weather is heading our way, and rain chances Thursday through the weekend will accompany the slightly warmer temperatures. :'(
After Sunday, the weather is anyone's guess
After Sunday, the models are having a really hard time figuring out what is going to happen. Will we retrograde back into a cooler-than-normal pattern or will we stay above normal? Autumn is notoriously hard to forecast and November is one of the hardest months. The Climate Prediction Center is forecasting above-normal temperatures for November through January (which seems to be driven by forecasts for a warm December), so we'll have to see if that plays out:
