Headed toward a chilly southern Canada vs. mild USA pattern for most of November….

The Arctic air mass that is dropping through the Intermountain Region and Great Plains may look ferocious, but the event is actually fairly normal for later October. The ridge pattern (-EPO/+PNA/-AO/-NAO) should flatten by next weekend, which in turn ought to allow milder Pacific Ocean origin air to overtake -most- of the lower 48 states. But therein lies a caveat!

Most of the model guidance suggests that one or two more cold fronts will pass through the Great Lakes and Midwest into the Northeast in the longer term. These intrusions will be of a polar (cP) nature, and more moderate than the current advancing Arctic regime. A weaker blocking signal over Alaska, northern Canada and Greenland will persist through mid-November. So while most of the USA warms up, places like Detroit MI and Philadelphia PA may stay on the cool side for a while longer.

I am also watching the formation of a tropical depression below Guatemala, which I suspect will become a hurricane and cross the Isthmus of Tehuantepec in about three or four days. This feature could merge with the aforementioned cold front, and it is within the realm of possibility that an extratropical frontal wave could threaten northeastern Mexico and much of Texas with another round of heavy rain.

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