A weekend of rain is expected for much of Bay Area. How heavy will it be?

"These are the tail end of the big system that's moving through the north, NWS meteorologist Rick Canepa said. So you're seeing the weak side of the surface low pressure as it approaches Northern California and our area. There's some good water vapor higher up, so you might see a lot more in the higher elevations. In other words, those who live near Mount Tamalpais and other areas of the North Bay where rain typically falls hard should batten down the hatches."

"Whatever rain does fall only will add to what already has been a significantly wet October. It is being created by what the weather service has called a small atmospheric river migrating from off the northern coast. The major impact of that system will land on Oregon and far Northern California. But there will be plenty left over to dump what is expected to be an inch in the North Bay and up to a quarter-inch closer to Contra Costa, Alameda and San Mateo counties."

"A second small wave from the tail end of the system is also anticipated to drop a bit more rain on Sunday night and possibly into Monday. it's likely to be highly variable, Canepa said. In a way, these kind of events can be really tough to forecast. It's the tail end of the this system, but that tail end could carry some decent precipitation."

A tail-end of a larger system will bring additional rain to the Bay Area this weekend, with the weak side of a surface low shaping rainfall distribution. Upper-level moisture will favor heavier precipitation in higher elevations and the North Bay, particularly near Mount Tamalpais. East Bay and Peninsula should see lighter amounts, while the South Bay may see little or none. Rain will add to an already significantly wet October. A small atmospheric river migrating off the northern coast is supplying the moisture, with major impacts farther north; a second small wave may bring more, highly variable rain Sunday night into Monday. Dense interior-valley fog preceded the system, briefly reducing visibility to a quarter-mile before expected clearing.

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