US September Outlook

Written by on August 13, 2013 in United States of America with 0 Comments

While it’s cool now across the Midwest and East, change is on the way as a Canadian high drops into the Southeast this week and it looks like we eventually see warming southwest winds develop on the backside of the high, allowing the Northeast to warm up considerably next week on into the following week. The upper pattern is changing across North America as we progress through August.

Following a chilly front running 7 days with temperatures likely to average 5-15 below normal from the eastern Plains to Atlantic, here’s the CPC temperature anomalies day 8-14 which shows warming taking place over the Northeast again with the cool pocket that’s vast now, sinking considerably.

814temp_new

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The warming that takes place between week 1-3 fits in nicely with the NAO set to turn positive for the first time in a couple of months, August would appear to end warm in the East or certainly from the Mid-Atlantic up into the Northeast but it’s likely to stay cool with plenty of rainfall in the Southeast. That means a warm start to September from roughly Washington DC north, however does that mean a warm September ahead in the East? I remain unenthusiastic about a warm September despite one source in particular heading for a warm East. I do think the Northeast bares watching as cool Canadian source highs drop southeast, they can kick up SW winds on the backside which allow above normal temperatures into New England while from NYC or Philly south it’s normal to below so that’s something to consider and it looks like the CFSv2 is seeing that. However I will stick to a cooler than normal September despite the likely warm start from DC south while it’s normal to perhaps 1 or 2 degrees above normal NYC to the Quebec border.

nao_sprd2

The NAO goes positive but I don’t see it staying that way given the trend this year. I believe the first week of September is warmer than normal from the Tennessee Valley up to New England the first 7-10 days of the month but I believe the NAO goes back negative and the troughs will return to the East from mid-month on from the Upper Midwest (Minnesota) SE towards Florida.

Here’s the CFSv2 temperature chart for September.

usT2mMonInd1

Interestingly the CFSv2 shows drier, not wetter than normal conditions from North Florida up through the Southeast where it’s been so wet right up the Eastern coastal plain.

usPrecMonInd1

As for the Western US, we should see the first real BELOW NORMAL temperatures to end August with a weak trough developing late August and into early September as above normal temperatures focus on the East but through week 2 and 3 I expect the ridge to rebound and temperatures should go back into above normal territory.

It’s been a very dry year from San Francisco to Salt Lake City but the month of September does look more promising in terms of rainfall, especially with lowering heights and Pacific systems pushing in.

Finally, the pool of warmer than normal water south of Alaska looks likely to support a ridge up into Alaska and Northwest Canada in the longer term so once the NAO flips negative once again which I suspect it will into early and mid September, expect the above normal trend to continue here. That upper pattern is likely to keep the Eastern Lower 48 below normal.

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I hope to release my US Fall Forecast later this week which looks at October and November as well as September..

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