Dry through Tuesday. More Rain on the Horizon for the North Bay.

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QUICK SUMMARY

Mostly sunny with mild weather (high 50s-low 60s) through the day after Christmas, December 26th. Then two storms may arrive within 3 days bringing moderate amounts of rain and wind to the North Bay and much of California.

THE DETAILS

Our recent storm, after dropping 3 plus inches of rain on much of California, is spinning east through the desert Southwest. High pressure will quickly build in, giving us mostly fair weather for the next 5 days.

There had been lots of hype about a deluge headed for California in the last week of December, largely due to a strong Pacific jet stream extended eastward toward California. This is still in the forecast, but the jet stream may be weakened and deflected south as it encounters high pressure over the Western U.S.

Here is the jet stream forecast for December 29th, clearly showing this.

And here’s the forecast high pressure ridge over the U.S. and Canada that will be interacting with the jet stream.

This isn’t to say that we won’t get rain, but the storms may not be as strong or wet as once expected.

Here is the first storm. The models forecast it to arrive in the North Bay on Wednesday the 27th.

This first one is expected to weaken as it reaches California, with much of its impact sent north into Washington and Oregon.

Here are early estimates of rainfall from Dec 27-29. Looks like 1/2 to 2 inches across the North Bay, with higher totals in the hills.

A second storm will follow close on the heels of the first. The European model has this one arriving on the 29th, while the GFS model holds it off until the 30th.

The first storm should “prime the pump”, weakening the high pressure ridge. This may set the stage for a somewhat wetter 2nd storm.

This 2nd storm (on the 29th or 30th) may be a two day affair. Here are the expected rainfall totals by the 1st of January. This includes the storm on the 27th.

So the 2nd storm may drop another 1 1/2 to 2 inches of additional rain. Some models are even wetter with this 2nd system.

So, between the two storms the last week of December may be fairly wet, with above average rainfall across our region. (This is the amount ABOVE average expected)

After that it’s all guesswork.

Both major forecast models and their ensembles show slightly above average rain for the first week of January. But you can see by the graphic below that the heavy rain has a hard time reaching California, as high pressure looks to remain centered over Canada and extend south over the Western U.S.

We’ll post more updates as the forecast evolves in the coming days.