San Diego Has Dodged a Bullet So Far, But Flood Risk Remains

The atmospheric river took its time, but eventually it ran through San Diego County.

It delivered about as promised, with more than 1.8 inches of rain falling in San Diego by 1 p.m. Tuesday, more than 4 inches soaking Palomar Mountain, and more than 6 inches drenching San Onofre.

The storm caused widespread flooding in and around Los Angeles Sunday and early Monday, but the bulk of the rain didn’t arrive in the San Diego region until after dark Monday.

“Sometimes, it’s not whether or not it will happen that’s hard to forecast, it’s the timing,” said Jonathan Rutz, an atmospheric scientist at the Scripps Institution of Oceanography.

The atmospheric river, a long, narrow plume of moisture that stretched thousands of miles to south of Hawaii, has moved on to the east. But there is no time to dry out.

The storm system that pulled the subtropical moisture north is not done with the region. Intense, intermittent showers are possible through Wednesday morning, including thunderstorms, and the threat of urban flooding remains.

Then come two more bands, one later Wednesday and another Thursday, with rain possible into Saturday, National Weather Service meteorologist Jonathan Suk said. All told, the San Diego area could get another 2 inches of rain before the week is out. 

If the coming storms deliver, San Diego could reach its annual average rainfall, 9.79 inches, just 10 days into February. The city has recorded more than 7 inches since Oct. 1, with more than 6 inches falling the last 18 days alone. Oceanside has had similar numbers.

Saturated soils have contributed to the flood risk. The San Diego River at Fashion Valley reached the minor flood stage (10 feet) early Tuesday afternoon, and it’s expected to stay around that level through Wednesday morning. The Santa Margarita River north of Oceanside was also on the edge of the minor flood stage.

Suk said some of the intermittent showers expected to move through the county Tuesday and early Wednesday could have high rain rates of 0.5 to 1 inch per hour. The showers, which could include thunderstorms, would likely be brief, but rain rates that high can create isolated flooding. The storm on Jan. 22, which caused damages in and around San Diego estimated at $90 million, exceeded 0.75 of an inch of rain during consecutive hours.

“The call to action for the public is, when you see a flooded road, turn around, don’t drown.” Suk said.

After Saturday, no big warm spells are on the horizon, but the region should have a week or so without rain. Looking farther down the road, forecasters are watching the possible development of another soggy stretch around Feb. 19. The forecast is too far out to bank on, but it has the potential to bring more heavy rain to the region.

Rutz, the Scripps scientist who works on atmospheric river predictions for the Center for Western Weather and Water Extremes, said forecast models show a much quieter period into next week, then a  chance for the resumption of an active pattern. But he cautions that forecasts more than 10 days out are less reliable.

Rutz said that more than a week in advance, the models did do a good job of predicting the last atmospheric river’s timing and extreme impacts in Los Angeles, San Bernardino and Orange counties. Those regions were pounded by the moisture plume for nearly 48 hours straight.

Predictions for areas on the fringe of moisture plumes, as San Diego County was, are often harder, Rutz said, Relatively small differences in location can make a huge difference in impacts. San Diego’s forecast did not come into clear forecast until Sunday, he said.

“Down here (in San Diego), it was a 12- or maybe 18-hour event,” Rutz said. “Down here, we kind of dodged a bullet.”