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As always at this time of year, a big concern across Northern California is the climate. How hot and dry it will be heading into the fall season, and the implications for wildfire.

There are positives, especially in the short term. High pressure over the West Coast now (Image 1) will give way this weekend to low pressure moving into the Pacific Northwest. (Image 2) That will cool us down over the next 7 days. (Image 3)

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As we get closer to fall, the long range models will come into better focus on rainfall outlooks. For now, a rather strong La Nina pattern continues in the tropical Pacific…with cool sea surface water becoming even more pronounced. The chances of that pattern persisting into the winter are large, with a neutral pattern (neither La Nina or El Nino) becoming more likely later in the winter and spring. (Image 4)

Historically, strong La Nina conditions have brought varied conditions to Northern California. There have been wet and dry seasons. But averaging them all out, on balance we can expect somewhat normal rainfall. Not very helpful.

Looking at the long range 30 day outlooks, there is a general consensus that the Pacific Northwest will be dry, and we may be near normal. Again, not too helpful since we normally don’t get a lot of rain in September. But at least we don’t seem abnormally dry. (Images 5 and 6)

Another plus right now. Most 30 day temperature outlooks, into late September don’t show us much hotter than normal. (Image 7)

As we get past September 1st, the long range outlooks of the major forecast models will weigh in with a bit more authority about the winter outlook. As we know, in the past La Nina has brought us both very wet, and fairly dry winters. The larger scale forces that drive La Nina and El Nino are simply presenting in this graphic. (Image 8)


You can see the cool water in the central and eastern Pacific with La Nina. That generally influences atmospheric patterns in a way that leaves NorCal between wet and dry. At that point smaller seasonal patterns exert a big influence over whether we tip wet, or dry.

But climate change has altered the variables, imputs and validity of the assumptions the models use. It will be interesting to find out what direction they move in relation to our fall season.

We’ll have those details as they arrive. Stay tuned!


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