The Cold Air is Coming!
The first fall cold snap of the season is coming for Friday and Saturday. Take a look at the picture above. The cold air right now is pooling in northern Canada. Most of October has been unseasonably warm with the cold air bottled up well to our north thanks to the zonal east/west flow of the jetstream.
That won't be the case toward the end of the week. A major ridge of high pressure will shunt the jetstream well north across the Pacific Northwest. The warming to our west will cause the cold air to plunge south. The air mass will modify some, but it appears that our first frost and freeze will occur for both Saturday and Sunday mornings.
The coldest we have been in Milwaukee this Fall (from September 1) is 54 for a high and 45 for a low. Expected highs on Friday and Saturday will only climb into the upper 40s! It's important to note that our average first frost is October 14th, and we usually see our first freeze between October 11th and 20th, so the cold air is really right on track.