Historic California rain could foreshadow more extreme rainfall in coming weeks

Southern California may have just experienced a historic amount of rainfall, but more extreme precipitation is headed toward the region.

More than a month's worth of rain fell in a span of three hours in San Diego on Monday, according to the National Weather Service. The city saw its wettest January day on record and wettest overall day in nearly 100 years on Monday with 2.73 inches of rain on Monday. Typically, San Diego sees an average 1.98 inches of rain in the entire month of January, records dating back to 1850 show.

The Southern California coast has been getting slammed with moisture this week, with up to 9 inches of rain falling in parts of the region over the weekend into Monday. Dozens of rescues were reported around San Diego County due to this historic rainfall.

While the area got a much-needed reprieve beginning on Tuesday, there is growing concern for multiple rounds of heavy rain targeting these same areas in California and other parts of the West beginning later next week and lasting through early February, forecasts show.

Southern California is expected to experience a period of dry weather through at least the upcoming weekend, but rounds of heavy rain are now targeting the northern half of the West Coast, with rain soaking the area from Northern California to Portland and Seattle on Wednesday afternoon. Another round of heavy rain is expected in the Pacific Northwest by Friday night into the upcoming weekend.

Following this storm system, much of the West will experience a brief break. But, the wet winter weather will not subside completely.

At the start of February, an active weather pattern will likely take shape across the West once again, bringing the chance for multiple heavy rain events during the first week of the month.

The extreme rainfall event that hit San Diego and the rounds of heavy rain in the forecast, particularly for southern California, have strong connections to the current El Niño event that is in place.

During the winter months, this leads to wetter than average conditions across much of the Southern U.S, including a large swath of California, according to the National Oceanic and Atmospheric Administration. A typical El Niño pattern favors multiple rounds of heavy rain and an overall period of unsettled, rainy weather.

In addition to El Niño, human-amplified climate change can play a role in extreme rainfall events, especially in the future as the impacts of global warming continue to worsen, experts said.

In the coming weeks, many of the potential heavy rain events along the West Coast will likely be fueled by atmospheric rivers. Atmospheric rivers, essentially rivers in the sky that collect moisture from tropical areas and redistribute the water to other latitudes, are natural part of the global weather system. But climate change is expected to impact the intensity and frequency of atmospheric rivers in the future as global warming leads to more moisture being evaporated into the atmosphere, according to recent research by NOAA.

Researchers found that models in higher temperature scenarios predicted increased low-elevation precipitation, but less high-elevation precipitation, research shows.

And it’s not just atmospheric rivers. Climate change can cause extreme rainfall events to become more frequent and more intense, research shows.

More intense extreme rain events also increase the frequency and scale of flash flooding as the influx of water is more than current infrastructure was built to handle, experts said.