MAJOR SHIFT: FROM COLD AND WET TO WARM AND WET

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The winter of 2022-2023 continues to amaze. Over the next 5 days California will transition from a cold and wet weather pattern to a warm and wet one. The impacts may be extensive and include flooding, especially in lower mountain areas with unusually large amounts of snow on the ground.

The pattern change is still 4 days away and the details are still sketchy. However the ensemble models are coming into good agreement on the change, if not the full direction and magnitude.

The satellite view Monday shows a cold low pressure system slowly moving south along the West Coast, sending waves of showers into California. As it passes south, it could and mostly likely will “phase” with subtropical moisture to the southwest, sending that plume into California. (Image 1)

Our cold showers will continue through most of Wednesday. After a break Thursday, both major models bring a substantial moisture plume to the California coast. (Images 2-3)

The ensemble models, which factor in lots of potential outcomes, all agree on at least a moderate AR plume arriving the 10th to the 11th. (Image 4)

Here in the North Bay, we’d likely feel the first effects in the afternoon on Thursday, with the rain picking up through Friday and continuing into Saturday. The European model outlook for late Thursday clearly shows the effects of the low moving down the coast helping to direct and funnel subtropical moisture into California. (Image 5)

The first atmospheric river plume could bring a substantial amount of rain to Northern and Central California and the North Bay by late Sunday. Early estimates are 2-4 inches for the North Bay, with the highest amounts in the hills. Notably, the European model in its latest runs in much wetter. (Images 6-7)

The models also disagree in how many significant atmospheric river events we will see. After Friday-Saturday, the GFS ensemble has other moderate to large ARs arriving around midweek. (Image 8) Other ensembles generally show weaker plumes reaching us.

All ensembles models show the next days 10 days to be wetter than normal for March. (Image 9)

And, although this may well change, the jet stream looks like it could be aimed at California into mid-March. (Image 10)

There are a lot of factors at work here, and as we always say, much could change. But it is important to be aware that the transition coming up could bring high impacts to our region, especially since we have been in a cold, showery pattern for the past few weeks.

The upcoming pattern change has the potential bring lots of much warmer rain to the region, similar to what we saw just after Christmas into the first part of January. We’ll keep you up to date.