September 2017 Weather Forecast: Southern California Long Range


August 2017’s forecast went flawlessly as it predicted the start of the month having the monsoon, then a break, and then the end month having a return of the storms and it did just that.  Now what about September?

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September is generally a transition month where we do see heatwaves and we do see cool-downs.  However I know many of you are looking for that cool-down since the end of last month and now is so hot.  We will be above average in temperatures for the start of the month before cooling down after September 14th.  Then… a trough moves over the Western United States and knocks that four corners ridge out of the area for good.  This is interesting because September 15th is the end of the monsoon season in the Southwest United States and this is exactly when that ridge will get knocked away.

This looks to maintain below average temperatures for September from mid-month all the way to the end month.  This could be interesting because usually around September 21st we see a bump up in temperatures … but not this time.  Looks to be like September will have the last half being colder than average so this will make a lot of you happy.

As for precipitation, precipitation is all over the place for the month, with some parts of Southern California seeing above normal and some parts below.  Generally as stated on August 23rd in my preliminary September 2017 forecast to the premium members, I said that a tropical influence would be likely for the first part of the month and here we are with a Tropical Storm south of us moving near the area by Sunday and then the door remains open for shots of monsoonal moisture … all before drying up.

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So I’ll go with above normal conditions for precipitation from now through September 11th, with drying conditions several days after then … and with th trough setting up for us after the 16th or so we may get return precipitation from impulses of the Fall Storm Season on the West Coast, but if they aren’t full blown storm systems it’ll be training weakening fronts with the normal storm season areas of Vandenberg, San Luis Obispo, Kern, and Ventura County seeing more rainfall than areas further east.

Hottest Periods – September 1st through 11th

Coldest Periods – September 14th through 30th

Wettest Periods – September 1st through 12th, Then monitoring 15th – 22nd


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