September has been a warm month for the Eastern US but it looks like it’s turning cooler for October and the month is likely to begin very cold compared to normal in the Plains. In fact snow and record cold is possible as bitter cold air parked over Alberta and Saskatchewan drops south down the Plains as strong ridging builds northward into Alaska.

However, a strong upper ridge over the Southeast looks to shield the east from the early season arctic outbreak and given the big thermal gradient between North Dakota and Georgia, we could see very significant rainfall in between.

With the greatest thermal imbalance in the front running 2 weeks, expect to see the heaviest rains during that two weeks and then as the cooler air spreads east, so the rains should be less.

Here’s Sept so far. Check out how cold it’s been over the western interior of Canada. Little mention of this…

Here’s the CFSv2 for October

I think the model is too warm in the east. Despite the very warm start, the dam should begin breaking with cold eventually reaching the east coast and so the month should wind up at or below normal.

The CFSv2 weeklies make sense showing the cold sinking south and east despite the full trough always hanging back over the Ohio/Tennessee valleys. That’s indeed a MEAN position over 7 days so periodically, the trough axis is likely to make it to the coast.

It also makes sense that by the end of the month with troughiness returning to Alaska that the ridge and warmth returns to the east.

2m temp anomaly

As for the tropics. Have you noticed the uptick in activity again following the abrupt shut down immediately following Florence?

Latest activity!

Large scale sinking returned to the western Atlantic just as Florence hit the Carolinas but it’s swinging the other way again with upward motion becoming widespread over the east Pacific and Atlantic while the west Pacific should shut down from now through the remainder of September into the first half of October.

The below chart shows red (sinking) and green (rising) air. While this should aid development, note the red’s return to the Atlantic late October so it should quieten down beyond the 20th. Let’s hope there’s not been a big hit by then.

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