The fire threat across the Western US has continued to grow over the past several weeks and the above chart says it all.

Persistently dry conditions, in fact record dry conditions all the way from Coastal Washington and Oregon extending over the continental divide has meant a a mere stray cigarette bud could be enough to start a fire and autumn rains/snows really can’t come quick enough to the bulk of the West and Northern Plains.

Speaking of Northern Plains, the heat returned in full force on Monday with temperatures rebounding back into the 100s up across central South Dakota. Gone are those frosty 32F readings found across parts of North Dakota during Sunday morning but it does look as though the chilly fall-like air from Canada won’t be far away from now on with models showing the return to fall-like cool by later this week.

The US weather map has become fairly benign with a very pleasant fall air mass extending from Chicago all the way to the East Coast with widespread lows in the 40s and 50s with low humidity. Will this last? No as the warmth now over the Dakotas will head eastbound as a new push of chilly air gets brought down by a trough Wednesday-Thursday, this will help 50s, 60s and 70s return to the Dakotas while the 80s and higher humidity returns to the Ohio Valley and Northeast.

The below ECMWF chart shows the downright hot back over the Dakotas, the fall cool over the East but this all transfers east and while the Dakotas cool back down (note the trough diving down out of W Canada), it’s heats up again in the East. By the later of the week, highs are likely back in the 80s all the way to Maine by Thursday but the pattern is now transitioning into a much more transiant fashion with warm surges following quickly by pushes of cool from Canada.

By Friday, an upper low spins over the eastern Dakotas and Minnesota and this is sure to bring highs back to the 60s, perhaps 50s for some.

The charts show a more significant push of downright cold air (by mid to late Sept standards) around the 20th which could well bring an end to the growing season for many across the Upper Midwest, Mid-Mississippi Valley, Ohio Valley and perhaps even the interior Northeast with a widespread night frost and freeze.

Check out this SPC chart for day 8-14.

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