'We don't want to cry wolf:' How forecasters predict LA's next huge rain storm

Data like that might be too noisy to say anything with a great degree of confidence.

But as the storm draws closer, those models will start to align a bit more, giving forecasters a better idea of what to reasonably expect.

"And so that would increase our confidence levels," Sirard said. "Once you get in that seven-day window ... if these ensemble models are still showing, say, 60% hypothetically, 5 or more inches in a three-day period — already, our antennas are up. And it's like, 'OK, we got a potential for something significant coming in.'"

As forecasters get even closer to the storm's arrival, they can employ higher-resolution, shorter-range forecast models.

At a certain point, there was enough confidence for forecasters to post an attention-grabbing warning on social media on Feb. 1, three days before the storm's arrival: "We are expecting a major storm with dangerous, even life-threatening impacts!"

In subsequent days, local law enforcement and elected officials — from the city of Los Angeles to Santa Barbara County — held media briefings about the dire forecasts that included National Weather Service meteorologists.

Such coordination between meteorologists and politicians hasn't always happened. Unforgettably, although the National Weather Service office in Monterey issued a flood watch three days before a significant storm landed on Dec. 31, 2022, San Francisco officials were caught unprepared by a record deluge that flooded swaths of low-lying parts of the city and left residents and business owners furious.

There have also been memorable misses. Fourteen years ago, an unexpectedly powerful, slow-moving rainstorm unleashed a torrent of mud that inundated more than 40 homes in La Cañada Flintridge, a far cry from an initial forecast of a light to moderate rainstorm.

The models for the storm earlier this month did adjust in the days leading up to the event. Initial projections about three to five days ahead of the storm suggested Santa Barbara and Ventura counties would get hit the hardest. But as it drew closer, there were growing indications that Los Angeles County would bear the brunt, said Ryan Kittell, another meteorologist in the weather service's Oxnard office.

That ended up being the case.

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