DECEMBER RAINFALL OUTLOOK FOR THE NORTH BAY

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SHORT TERM

High pressure off the California coast will be the main feature of our weather for the next week or so. A few storms will brush Northern California, but most Pacific moisture will be funneled into the Pacific Northwest. By mid-month there are hints of a change to at least somewhat wetter conditions for Central California.

RIGHT NOW

High pressure off our coast continues to send storms into the PacNW, hammering them with rain.

Through around mid-month, very little moisture may reach California, outside of the far northern part of the state. We may get brushed by storms at times, like on Saturday, when a tenth of an inch or two of rainfall may push south into the North Bay region.

But overall, despite occasional showers that may push in from the north, we’ll be on the southern fringe of the storm track for another 7-10 days.

The best chance for heavier showers to reach us in the next 10 days is around the 7th or 8th, as a strong storm tries to “flatten” the high pressure dome.

Otherwise though, no big changes through the 15th or so. That’s when the weather outlook gets a bit more interesting.

The ensemble runs of the major models agree that a low pressure trough will finally displace high pressure off of the California coast. This would be around the 3rd week of December, 15th-21st.

The jet stream is forecast to dip south for the (possible) storm on the 7th-8th of December (next Thursday-Friday) , and then again after the 15th. That would correspond with a (more typical) El Nino shift south in the jet stream.

The trouble is, the correlation isn’t that strong. So the pattern may open up giving us more storms, but they may not be that strong or wet. The models pick up on that, showing greater than average rainfall for the 3rd week of December, but not hugely so.

In the longer range, the current sea surface temperatures (in the measured Nino 3.4 Zone) show continued warming, indicating a very strong El Nino is still gaining steam this year. In the past such a situation typically brings bigger rains for us in late December or January.

The second graphic shows the El Nino is still expected to peak in January and February.

This agrees with the current uber long range outlook by the Climate Forecast Service, for El Nino rains to kick in for Central and Southern California (and the North Bay) during January and (especially) February and March.

We’ll keep you up-to-date as the forecast evolves.