Flood Watch in California: Upcoming Storm Forecast
A Flood Watch has been issued for interior Mendocino and Lake Counties, California, due to an incoming cold front associated with a powerful atmospheric river. This weather event is expected to bring significant rainfall from late November 12 through Thursday morning, November 13.
Key Weather Forecasts and Warnings
The National Weather Service (NWS) indicates the potential for flooding as the storm moves through. Urban areas, particularly around Ukiah and Clear Lake, face heightened risks with the strongest rainfall anticipated near Cobb in southern Lake County. The NWS predicts rainfall totals ranging from 50-75 mm (2-3 inches), primarily concentrated in a 6-hour window early Thursday morning.
Flood Risks and Impacts
The swift accumulation of rainfall raises concerns for roadway flooding and urban drainage challenges. Locations with inadequate drainage systems are most susceptible to minor to moderate flooding conditions. Furthermore, the combination of heavy rain and steep terrain increases the likelihood of rockfalls and landslides along roadways, urging motorists to exercise caution during these conditions.
Detailed Atmospheric Conditions
The atmospheric river affecting the region has emerged offshore, linked to a deep upper-level trough characterized by enhanced subtropical moisture. The Center for Western Weather and Water Extremes (CW3E) describes this phenomenon as a robust atmospheric river with integrated vapor transport (IVT) exceeding 750 kg m-1 s-1 over northern California.
Forecast models from both the Global Ensemble Forecast System (GEFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) indicate varying AR 5/AR 3 conditions, with precipitation levels expected to considerably exceed the average for this time of year.
Broader California Weather Outlook
The NWS Weather Prediction Center (WPC) forecasts increased rainfall across much of California, estimating 50-100 mm (2-4 inches), and potential localized amounts over 100 mm (>4 inches) in the coastal ranges and Sierra Nevada. This storm could contribute 5-10% of the annual rainfall for several catchments when factoring in freezing levels that are relatively high, limiting snowfall primarily to the highest Sierra Nevada elevations.
Additional Flash Flood Watches
In tandem with the flood watch in Mendocino and Lake counties, there is another flood watch in effect from Thursday morning through Friday afternoon, November 14, covering parts of the Mariposa-Madera foothills, Yosemite Valley, and the San Joaquin River Canyon. Heavy rainfall in these regions could exacerbate river levels and low-lying areas.
Marine Warnings and Precautions
Adjacent to northern and central California coastal waters, multiple storm and gale warnings are enforced. Areas from Point St. George to Cape Mendocino may experience southeast winds of 55–75 km/h (35–45 mph), with gusts potentially reaching 95 km/h (60 mph). Mariners are strongly advised to stay in port and prepare for hazardous conditions.
Continuing Weather Alerts
The NWS San Francisco Bay Area has issued warnings for coastal waters extending from Point Arena to Point Reyes, predicting southeast winds of 35–65 km/h (20–40 mph) and possible seas reaching 2.5–4.5 m (8–15 feet). Similar warnings extend to the outer waters, emphasizing the need for vigilance and cautious navigation.
Conclusion
The upcoming atmospheric river and associated weather patterns signal a period of heavy rainfall and potential flooding across Mendocino and Lake counties together with other parts of California. The NWS strongly urges communities and travelers to remain informed of evolving weather conditions and take all necessary precautions.
For more updates on atmospheric river forecasts and their implications, visit the Center for Western Weather and Water Extremes (CW3E). Stay safe and prepared.
