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Weather forecast models have been offering tantalizing hints that the start of California’s rainy season may be just around the corner. However, until now, almost all of the action has stayed north. Not uncommon at this time of year as the models struggle with the change of seasons.

Now the latest runs of all of the models are once again suggesting the launch of our rainy season may be very near. Yes, we’ve heard this before, but stay with me.

By November 1st, deep low pressure is forecast to drop just off the California coast as high pressure retrogrades to our west, clearing the way. The models agree on this.

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This may set the stage for a burst of moisture. The European model has the first rain arriving just after Halloween evening, early on the 1st of November.

The models differ somewhat on timing and on whether another storm will arrive a day or two later, or if the first storm will just continue. Here is a second storm arriving on November 3rd, according to the Canadian model.

The models also vary in the amounts of rain we can expect through the first week of November. The Canadian and European are wetter than the GFS. Here is the National Blend of Models.

That may be optimistic, as the models have a history of pulling back as the arrival of the storms approach. But that’s the output right now for rain by next Sunday the 6th.

It is natural to be a bit skeptical of all of this in drought weary California, especially in a La Nina year. If you look at the individual members of the European ensemble model, about 20% of them show a fairly dry scenerio through the 9th of November, while 80% show somewhat wet to very wet. This is 25 of the 50 ensemble members as of Thursday the 27th. The other 25 are similar.

So what’s the big takeaway? First, that rain is definitely becoming more likely for the North Bay, arriving just after Halloween. Second, that Tuesday-Thursday of next week look like they could be the wettest period.

Finally, going into the 2nd week of November there are more tantalizing hints (yes, that again) that we may see another wet period. The GFS Ensemble outlook suggests a broad trough over California.

And both the European and GEFS long range outlooks suggest wetter than normal for the 2nd week of November.

Yes, still very theoretical, but as we get closer and the model agreement continues, these kind of rainy periods become more likely to occur.

One further positive sign is the CFS v2 precipitation anomaly output, which is generated daily using new data. It has become increasingly bullish on a relatively wet November. Here is it for your amusement. We hope it comes true. More updates to come.


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