This is a much longer and in depth forecast discussion than I usually post, but dangerous conditions are forecast so everyone needs to be focused on situational awareness and safety for themselves, their families, and their neighbors.
An approaching atmospheric river (AR) will begin to up the ante later Monday and for the second time in one week. Models are trending upward as to the strength of this AR. Integrated Water Vapor Transport numbers around 700 kg/m/s, combined with a low- level jet now showing the potential for 60 knots, is now making this a strong AR. This will be similar to the AR that was just experienced, if not stronger. Models have trended upward to reflect the increase in intensity of both the winds and water vapor associated with this plume of heavy moisture. Ensembles of both the GFS, ECMWF and Canadian are all showing a majority of members with heavy rainfall. Additionally, the EC originally was showing a more northward track while the GFS showed a track directed straight for the Bay Area. Those have come into better alignment with the bullseye now being more focused to the Bay Area and Central Coast region. Due to this, a High Wind Watch is in effect from Monday evening through late Tuesday night for southerly winds 25 to 40 mph with gusts up to 50 mph in the valleys. Expect gusts from 55 to 70 mph along the immediate coastline and in the hills above 1,000 feet. This will be for the entire San Francisco Bay Area and Central Coast. Fully saturated soils plus winds of this nature could create a potentially dangerous situation. Trees and power lines will fall easier than the last AR, putting everyone at risk. Travel will be hazardous for the Tuesday morning and afternoon commutes. It is best to delay travel. Additionally, a Flood Watch is also in effect from Monday evening through late Tuesday night for the San Francisco Bay Area and Central Coast. This is due to flooding caused by excessive rainfall being likely which will lead to creeks and streams rising out of their banks. Extensive street flooding and flooding of creeks and rivers is likely. Further compounding this issue will be the elevated water levels due to the most recent AR event. Areas such as the North Bay, East Bay and South Bay will see renewed flooding. Additional rainfall associated with this second AR will exacerbate ongoing flooding across Monterey County. There is an extremely high level of concern regarding the prolonged duration of flooding as all mainstem rivers will be elevated before the next AR makes landfall. Major interstates and highways can flood. Urban flooding, flash flooding and mainstem river flooding will be worse than last week. Widespread shallow landsliding is likely along with debris flows. Once again, travel will be dangerous for the Tuesday morning and afternoon commutes. Postpone travel! If you do travel (but don`t) turn around, don`t drown! Now is the time to prepare. Get gas for generators, food and medications. Clean storm drains and gutters. Tie down or move loose objects inside. Along with the trees falling, power outages will happen, yet again. This is a potentially dangerous situation as it comes so quickly on the heels of the last AR. Expect prolonged, long-fused impacts associated with these back to back storms even when the storm moves out of the area. This is looking to be likely Wednesday with conditions continuing to dry out into Friday. The dry air will usher in colder temperatures with the potential for higher elevations to drop to around freezing. After this, chances for rainfall could return for Friday and Saturday, however, confidence is low at this time.
