The East Pacific oscillation, or EPO, has a positive and negative phase. In the positive phase, a stormy pattern in the West and warmth in the East is a common sight. However, these two agencies are both predicting a very negative pattern. This would lead to an enhanced potential for cold air to work its way into the East, while high pressure sets up across the West.
These two indices look to produce a very chilly first week of October for the East. I would not be surprised to see cities like Chicago, Milwaukee, or possibly Indianapolis reaching into the 30's, possibly getting below freezing at times.
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