City officials squarely blamed a lack of preparation on incorrect weather forecasts from the National Weather Service — but the agency disputes that and has communications with the city to back it up.
“We were under the impression and notified by our National Weather Service that we could anticipate not even an inch of rain,” Mayor London Breed said at a press conference on Tuesday.
Instead, San Francisco saw its second wettest day on record, with a staggering 5.54 inches falling within a 24 hour period. The discrepancy forced the city to scramble after the rain began, officials say.
“We activated our (Emergency Operations Center) late morning when we realized that what was happening was a little different than the actual forecast,” said Mary Ellen Carroll, executive director of San Francisco’s Department of Emergency Management.
The Emergency Operations Center, or EOC, coordinates response efforts by city agencies and partners during major events, said Victor Wai Ho Lim, a spokesperson with the Department of Emergency Management who leads public information at the operations center.
Officials said that San Francisco was not prepared for the New Year’s Eve downpour because the National Weather Service indicated only half an inch to three quarters of an inch of rain would fall. The Chronicle was unable to determine where that number came from based on NWS forecasts.
Yet, San Francisco had been included within the boundaries of a flood watch issued by the National Weather Service days in advance that encompassed the entire Bay Area, and NWS spokesperson Susan Buchanan disputed the characterization that the agency had failed to indicate the potential for serious rainfall.
“Forecast Discussions issued by the National Weather Service’s San Francisco/Bay Area office beginning on December 21 alerted for a significant rain event that would bring high impacts and hazardous conditions, given that the soils were already saturated from previous rain,” Buchanan said by email.
These hazards, including flooding and debris flows, were shared with Bay Area officials in the days leading up to the storm through daily emails and a virtual citywide planning meeting for New Year’s Eve on December 28, Buchanan said. By December 29, the briefings called for 2 to 3 inches of rain for the immediate San Francisco Bay Area, with the potential for up to 6 inches in surrounding areas.
“Heavy rain with the frontal passage will likely lead to flooding along with wind gusts to 50 mph,” the NWS forecast discussion read at 3:29 p.m. on Dec. 30.
When asked to respond to NWS’s statement that the city had not been adequately warned about the storm, San Francisco’s department of emergency management said it considered NWS “an important and valued partner” and thanked the agency for its work.
“It’s a difficult job, and they do it well and with incredible professionalism,” Francis Zamora, chief of staff for DEM, said. “We realize that previous statements were seen as critical of our partners. This was not the intent of the comments made, but rather to simply state that the level of rainfall we received on New Year’s Eve was beyond what was predicted.”
That said, the forecasts didn’t account for the historic amount of rain that fell in San Francisco. Weather models underestimated the rainfall over the weekend because the storm system didn’t behave as expected.
“The European weather model was expecting between 2 to 3 inches of rain during the height of the New Year’s Eve storm in San Francisco,” said Chronicle Newsroom Meteorologist Gerry Díaz.
The NWS forecast discussion at 3:29 p.m. on Dec. 30 said: “The front will move through the heart of the Bay Area Saturday morning and then reach the Central Coast late morning through mid-afternoon. One item in our favor is the fairly fast movement of the system should preclude widespread significant flooding.”
Instead, Díaz explained, “the storm stalled over the peninsula for several hours longer than what the models had anticipated.”
With soils soaked by this earlier deluge, another serious storm system arrived in the Bay Area Wednesday morning, propelled by a bomb cyclone spinning off the California coast. The region is primed for widespread flooding, downed trees and mudslides as heavy rains and strong winds sweep across areas already saturated by previous rains.
To prepare for Wednesday’s storm, the city planned for additional rainfall, beyond what was forecast, officials said in the Tuesday press conference.
The Department of Public Works swept storm drains and distributed sandbags to residents to prevent flooding. The Department of Emergency Operations also activated an Emergency Operations Center with staff in-person at a physical location.
“Even though we anticipate anywhere between 2 and 3 inches, we’re going to be prepared for even more in light of what just happened this past weekend,” Breed said on Tuesday.
Chronicle staff reporter St. John Barned-Smith contributed to this report.
Jack Lee (he/him) is a San Francisco Chronicle staff writer. Email: jack.lee@sfchronicle.com
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