Atmospheric River Update: Rainfall Events Expected for Southern California Starting November 15

An atmospheric river is expected to bring rainfall events to southern California this week, bringing the risk of flash flooding in urban areas, including Los Angeles, and low-lying areas. This California weather forecast is according to the National Weather Service (NWS), which predicts the occurrence not only of rainy precipitation but snowfall as well in high-elevation areas.

The so-called weather event, atmospheric river or "rivers in the sky", resulted in widespread flooding across parts of California earlier this year. Now, the current system is caused by a Pacific storm located off the coast of the Golden State, where moderate to heavy rain is imminent by midweek and possible until the coming weekend.

Southern California Weather Forecast

The southern California weather outlook this week was issued by the NWS Forecast Office in Los Angeles, California, indicating that multiple waves of rain are in store for the state starting Wednesday, November 15. The weather alert published by the NWS at 1:10 p.m. local time on Sunday, November 12, shows that there is 100% chance of rain from midweek until Saturday, November 18.

Furthermore, southerly winds with gusts of 30 to 50 miles per hour are likely from Wednesday to Friday. Meanwhile, snowfall is also possible at elevations of more than 8,000 feet, meaning snow hazards will not be a concern for the region.

Heavy Rain Alert and Advisory

The US weather agency also mentioned that the following counties are at risk due to the lingering Pacific storm train. It added that the chances of rain can begin as early as Tuesday night, November 14:

• San Luis Obispo
• Santa Barbara
• Ventura
• Los Angeles

The NWS advices the public to exercise the following actions ahead and during rain and flooding events:

• Clear out rain gutters to prevent flooding
• Reconsider engaging in outdoor activities
• Avoid traversing flooded streets and highways
• Stay up-to-date with current forecast and monitor local weather developments

This week's atmospheric river-driven rainfall events are expected to cause disruption to local travel and road traffic, as well as power outages since strong winds can damage power lines.

Atmospheric River Phenomenon

An atmospheric river is a narrow column within the Earth's atmosphere, a region where it transfers the majority of the water vapor that can be found in the outskirts of the tropics. These rivers in the sky differ in size and intensity. The NOAA says that the average atmospheric river contains water vapor approximately equivalent to the normal water flow at the mouth of the Mississippi River.

Meanwhile, a strong atmospheric river can transport water vapor up to 15 times the normal amount. In March 2023, California authorities declared an emergency after an atmospheric river. The storm caused dangerous flooding due to heavy rain. It also led to heavy snowfall and howling winds across the state.