Two potent storms are headed for the San Francisco Bay Area. How much rain will we get?
The Bay Area got some widespread showers to dampen Valentine's Day activities, but the rain projected from two incoming storms starting this weekend will be far heavier.
While the systems won't be quite as intense as the atmospheric-river event that caused localized flooding, downed trees and power outages almost two weeks ago, they are going to dump a substantial amount of rain across the region.
The storms will bring the potential for moderate to rapid rises along area creeks, streams, and rivers across Northern and Central California. Soil moisture remains high from earlier storms this month and will reach saturation this weekend as the first of the cold fronts moves through the area.
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Currently, models indicate showers will start rolling into Northern California from offshore late Friday evening as the first system arrives with rain intensifying over the course of Saturday. Between Friday night and Sunday morning, the North Bay and coastal ranges will pick up in the range of 1"-3".
The first round of heavy precipitation has the potential to produce isolated flash flooding across the central to northern California coastal regions, according to the National Weather Service.
Rain will not be the only impact from this system. Strong southerly winds will precede the frontal passage. High surf will begin to impact the beaches on Saturday, with large breaking waves in the 18-22 foot range from a combination of strong winds and incoming westerly swell. A High Surf Advisory will be in effect from 10 a.m. Saturday until 4 p.m. Sunday.
After a brief break early Sunday, the second storm system moves into the Bay Area Sunday night, with heavier rain on Monday morning to kick off the work week with the lingering atmospheric river event continuing to bring rain to the region through Tuesday.
By Wednesday morning, the highest rain totals are forecast to fall in the Santa Cruz Mountains with up to 7.5" in Ben Lomond. The North Bay will also see significant rain, with Santa Rosa likely topping 4" and San Rafael possibly getting as much as 5".
Most other parts of the Bay Area including San Francisco, the South Bay and interior parts of the North and East Bay are projected to get between 2"-3" through Wednesday, with slightly higher totals possible on the Peninsula.
Models suggest the greatest accumulation of precipitation will be observed along the coastal ranges. The National Weather Service said rainfall totals should remain consistent with 1 to 3 inches expected across most areas with 3-6 inches expected over favored peaks and higher terrain of the coastal hills and mountains.
USGS instrumentation throughout the San Francisco Bay Area indicates that shallow soils on steep hillsides are approaching saturation. This coupled with the forecasted precipitation means shallow landslides are possible.
Once saturated, additional rainfall will runoff resulting in moderate to rapid rises on our creeks, streams, and rivers, as well as lead to nuisance and/or minor flooding. Localized ponding of water in low-lying or poorly drained areas, such as freeway offramps is expected.
The river forecasts from the California Nevada River Forecast Center (CNRFC) depict an initial rise on area creeks, streams, and rivers on Saturday and Saturday night, with a larger rise on Monday and Tuesday.
However, the latest update from CNRFC lowered the probabilities of reaching flood stage for most of the rivers. The current guidance indicates the Russian River in Guerneville, the San Lorenzo River in Big Trees and the Carmel River in Robles del Rio have a 20% chance of reaching flood stage in the next five days.
Although the current forecast shows these creeks and rivers remaining below flood stage, some locations may reach monitor stage.
The Sierra could see up to 30 inches of snow accumulating up through next Wednesday.
