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Two days before the arrival of the first storm along the coast, all signs now point to a huge and impactful storm series headed to California and the North Bay. The first storm will arrive late on the 26th, and rains, heavy at times, will continue off and on until January 2nd at least.


Atmospheric conditions appear to be setting up just right to bring a series of as many as three strong moisture plumes to the California coast over the next week. The timing and exact location of the atmospheric river plumes is coming into sharper focus as the events near. The North Bay and areas of the North Coast should be in the bullseye for at least 2 of the most significant rain events.

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Even the widest satellite view doesn’t capture the series of storms headed to the West Coast. But you can clearly see a zonal pattern (straight line) of storms far out into the Pacific west of California.

These will spin up into moderate to major storms as they ride a very strong zonal jet stream, developing along the border between high and low pressure, into California and the Pacific Northwest.

The first storm will arrive late on Monday the 26th. It will carry a strong to potentially extreme AR plume to the coast. During the day Tuesday the plume will drop south along the California coast.

The Western Center for Weather and Water Extremes rates this storm at strong or better (level 4) as it is forecast to arrive on the Sonoma and Mendocino County coasts late on Monday the 26th and early Tuesday the 27th.

By that time the strong jet stream will have established itself across the Pacific from near Japan to the West Coast of North America.

And along that boundary, storms to the north will stream into California every 24 to 36 hours from Monday the 26th through the Saturday 31st, and potentially through the 3rd or 4th of January.

The first storm is shown arriving via the European model late Monday.

And the best estimate of rain from this first, potentially very large storm by Tuesday afternoon the 27th.

Here the models are split. Some see the rain continuing through Wednesday with little break. Most show another storm arriving early Thursday the 29th.

By Thursday afternoon, the total rainfall should be adding up.

Most models have another storm arriving early on the 30th, and another for the 31st.

The storm on the 30th-31st could bring another big moisture plume to the coast.

Projected rainfall by Friday across the North Bay.

One of the biggest storms of the series may be on the 30th and New Year’s Eve, the 31st. However this is too far in the future to be sure. Here is the AR forecast, which shows a big uptick in moisture expected with that storm.

Whatever the case, the ensemble models as well as the blended models (averaging various model outcomes) show lots of rain across California and the North Bay by the 1st of January.

AND, early signs point to another, potentially strong storm for Monday the 2nd. But more than a week out, much could change.

So, the overall message is that a big storm series, the largest of the year, is inbound. These storms will be fairly warm as they are drawing in subtropical moisture, so temperatures will remain in the 50s for the most part, with 40s at night. And flooding is not expected to be significant, and if it does come it should be mostly small creek and urban street flooding, especially with the first storm on Tuesday.

And, while we should pick up lots of beneficial rain, it will fall over many days keeping the risk of river flooding to a minimum.

We will have more updates in the coming days as the first storm in the series arrives along the coast.

Stay tuned!

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