September kicked off a beautiful start to the fall season. In fact for awhile, it almost felt more like summer than fall. But starting with the end of the September, a change in the jet stream meant a big time temperature swing.

The jet stream is a strong upper level wind flow that acts to divide warm and cold air masses. During September, the jet stream was well off to the north, which meant temperatures were warm. However, by the last few days in September, the jet stream plunged south, ushering cold air into Wisconsin.

That pattern has stuck during October and through the first 14 days, every day has been below average. It is far different than September which had only 6 days below average.

So far in October, the average temperature is running around 7 degrees below average in Green Bay, with La Crosse running around 11 degrees below average.

With these statistics in mind, it is no surprise that it has been the 5th coldest start to October on record in Green Bay. Meanwhile, in Wausau it has been the coldest start to October.

Until Next Time,
Meteorologist Andrew Thut