FLOOD CONCERNS GROW: SHOWERS, THEN ANOTHER BIG ATMOSPHERIC RIVER

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More than a week ago we said March may be a lion. That has so far come to pass as another strong AR moisture plume is forecast to reach Northern California late on Monday. But before that we’ll be in a moist onshore flow, with embedded waves that will bring us light to moderate rain at times all weekend.

You can see all of that in the latest satellite view:

Looking further out in the Pacific, we can see the next atmospheric river taking shape. It is the prominent atmospheric wave and moisture plume to the left of the picture.

A strong southern branch of the jet stream continues to direct subtropical moisture and storms to California.

Through Sunday we’ll be in a moist onshore flow, but with different origins and therefore a bit cooler one than what’s on the way for late Monday-Tuesday.

Regardless, waves in the flow will enhance rainfall at times including what we’re seeing Saturday, then again early Sunday morning.

Total rainfall amounts through Sunday evening may look like this. Perhaps another inch across the North Bay.

Really, with the continuous moisture flow over us it will seem like the rain spigot never gets shut off. In fact, showers will continue at times Monday before the next main event, yet another atmospheric river storm, arrives with big rains late on Monday.

This one will once again have a plentiful subtropical moisture feed.

Heavy rain will begin overnight Monday-Tuesday, and by the time of the Tuesday AM commute, the storm will be near its peak in the North Bay and Bay Area.

By late Wednesday we could see 3-4 inches of additional rainfall from the storm, most of it falling early AM through the afternoon on Tuesday.

With the ground super saturated, runoff will be immediate as will quick rises in small streams and flooding of roads. Also expect debris flows and rock slides on steep hillsides.

And, with huge flows once again funneling into the Russian River, the mainstem may be in danger of flooding in Guerneville, Hopland and elsewhere. Here is the forecast for the Russian at Guerneville. Rising to the 29 ft monitor stage on Tuesday, and getting very near flood stage of 32 ft on Wednesday.

The more flood prone stretches of the Russian River, like Hopland, may exceed flood stage on Tuesday.

Smaller streams will rise quickly, and the Laguna de Santa Rosa at Sebastopol will cause concern in low lying areas near the city.

The National Weather Service has issued Flood Watches for the entire North Bay, Bay Area and Central Coast as the Monday-Wednesday AR approaches.

Further ahead, it looks like rain may continue at times into the 3rd week of March. After that, there are hints the storm track may be moving away from California.