The Brief

Several days out from this latest storm, I spoke to a number of meteorologists and was told the weather models are all over the place, so we don’t quite know what’s going to happen. It could hit L.A. hard or peter out.

It was interesting to hear, as I cover climate and weather in Southern California, and forecasts usually seem a bit more confident in the four or five days leading up to a weather event.

Turns out, this storm and the conditions surrounding it were so wildly complicated that weather models were having trouble settling on what was going to happen.

“The dimension, scale and motion of the big feature that’s driving the large-scale weather pattern…that’s what’s different about this,” said Ariel Cohen, the meteorologist in charge at the National Weather Service in Oxnard.

Precipitation on its way to California on February 16, 2024

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Cooperative Institute for Research in the Atmosphere

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Modeling the interaction of various atmospheric features — from the atmospheric river off the west coast to the storm system up near Alaska — can be a struggle. Especially when models are trying to project several days out and anticipate what rainfall is going to be like at a neighborhood scale.

“That storm system that’s up near Alaska — how’s that going to move forward?” said Paul Iñiguez, a meteorologist with the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography. “If it went faster than we expected or it went slower than we expected, that's going to impact how it interacts with that decaying atmospheric river that's laid up on the west coast.”

One set of variables could lead to heavier precipitation in L.A. while another could mean lighter.

People view the Los Angeles River swollen by storm runoff as a powerful long-duration atmospheric river storm, the second in less than a week, continues to impact Southern California on February 5, 2024 in Los Angeles, California.

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What are weather models?

Meteorological agencies around the world simulate global weather multiple times a day. The National Oceanic and Atmospheric Administration does it every six hours and projects 15 days into the future.

They can take data from satellites, balloons, airplanes and weather stations, and use equations that represent our best understanding of the physics that govern the atmosphere, the ocean and the cryosphere to project weather on the way. And they switch out variables to calculate different potential outcomes.

“There are fundamental limits to how well you can do it because the atmosphere is chaotic,” said Tapio Schneider, a professor at Caltech. “Chaotic means that what happens later is sensitively dependent on the initial condition, on the state right now. So there's a fundamental limit to how well you can predict the weather, something like two weeks or so, beyond which you cannot say in detail what weather will be like.”

The closer you get to the actual event, the more predictable the outcome.

Though the models have improved substantially over time, even within those two weeks there are big limitations.

The limits to modeling

We don’t completely understand how the weather works or all of the global processes that influence every little thing that happens. Our monitoring equipment around the planet is limited in the amount of data it can give us, as we don’t have probes covering every mile. And there’s a computational limit to just how much data we can process at once.

The models see the planet as a three dimensional grid of data, with the little squares extending from the surface, high up into the atmosphere.

A view of the L.A. River on Monday shows high water levels and a swift moving stream on a river that's often bone dry.

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Just consider for a second the scales of interactions — from clouds swirling over the Gulf of Alaska down to rain falling on Topanga canyon.

“Think about everything that’s smaller than a few kilometers. That’s clouds, cloud droplets. None of these things you can simulate accurately with the current computational power or any computational power we can foresee getting in a decades to come,” said Schneider.

The more localized the projection, the more accurate the forecast, but the higher the computational cost.

Because of that cost, there are limits to how granular the models can get. Which is why there are inaccuracies when forecasting down to a local level, especially in a place like Southern California, which has wildly varied terrain that results in 20 degree temperature differences just a few miles apart.

Mudflows inundate a street in Beverly Hills.

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Should you take forecasts seriously?

Yes. With the understanding that even if you get a warning from the National Weather Service about a hazard like a flash flood, you may go through a whole lot of prep that doesn’t actually need to be used.

At the end of the day though, on the off chance that an extreme scenario does occur, it’s worth getting your stuff together.

I’d rather be disappointed than unprepared and caught off guard.

The Democratic National Committee on Wednesday sued President Donald Trump’s administration for recent television advertisements that promoted his political message while costing taxpayers millions of dollars.

The complaint, filed in the U.S. District Court for the District of Columbia, alleges that the ads are illegal government-sponsored propaganda and accuses Trump of personally directing them. It asks the court to declare the ads illegal and stop the use of federal funds to pay for them.

Trump has faced bipartisan backlash for the ads, which glorify him and echo his campaign pitch as voters cast early ballots with the midterm elections less than a month away.

The spots, which began airing in September, already have cost more than $12 million to run, according to the media tracking firm AdImpact, and a total of $20 million in Homeland Security Department funding has been tapped to pay for them.

Responding Monday to the criticism, Trump defended the ads as “positive promotion for our Great U.S.A.” but said he’d pay for them using his MAGA Inc. super PAC going forward.

But on Tuesday, the fifth ad in the campaign began airing with the notice “paid for by the U.S. Government,” promoting Trump’s military actions in Venezuela earlier this year. The same day, Trump made it clear he hasn’t committed to reimbursing any money that has already been spent, telling reporters “we’ll decide.”

DNC Chair Ken Martin said in a statement that Trump is misusing taxpayer dollars in “a last-ditch attempt to save Republicans in November.”

“Americans deserve better than to have their hard-earned tax dollars used for Trump’s illegal schemes,” he added.

Legal experts have suggested the ads run afoul of a federal statute against congressionally appropriated money being used for “publicity or propaganda,” and potentially other federal laws. The Homeland Security money tapped for the ads comes from a $175 million package Congress gave to the department as part of Trump’s immigration enforcement agenda.

The White House has defended the ads as public service announcements akin to what past administrations have done to promote various policies. Legal experts have said the recent ads differ from many past public service announcements because they aren’t aimed at helping members of the public benefit from specific government programs.

The defendants in the lawsuit — Trump, the White House, DHS and the Office of Management and Budget — didn’t immediately respond to requests for comment.

Fall has only just begun, but it's already time to start thinking about the quintessential winter bug: the flu.

The annual flu season usually starts in October or November. But this year, it looks like the flu started to pick up in early September.

"There are enough signs pointing in the same direction to make me think, 'OK, yes. This is the start of flu season,'" says Caitlin Rivers, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

The percentage of people testing positive for the flu in the West has been rising steadily since around the beginning of September, she says. And the number of people showing up in emergency departments because of the flu has also been rising for weeks, she adds.

"It's very uncommon to see flu activity rising this early. It's activity that we might normally see more like November or December," she says.

The timing of the flu season isn't the only thing that's odd. It's also unusual that flu activity seems to have started in Western states, such as California, Washington, Hawaii and Alaska.

"It typically starts in the South and then expands from there," Rivers says. "So two uncommon developments there."

Rivers stresses that the amount of flu activity is still very low in most parts of the country. But that's starting to change as the flu picks up nationwide.

It's unclear why flu activity would have started so early, and in such an unusual part of the country. But one clue might be a new variant that evolved a mutation, which appears to make it better at evading existing immunity, especially among teenagers.

"That's our best argument for what's going on right now in terms of this early flu season," says Dr. Alex Greninger, a virologist who heads infectious disease diagnostics at the University of Washington. Doctors there are seeing as much flu right now as they usually would around Christmas, and the mutated variant appears to be common, he says.

So Greninger, Rivers and others are urging people to think about getting their flu shot earlier than usual.

"It's crucial that people get an influenza vaccine," says Scott Hensley, a virologist at the University of Pennsylvania. "And this might be a year that people might want to get a vaccine early."

But the Centers for Disease Control and Prevention hasn't been promoting flu shots as it usually does. Health Secretary Robert F. Kennedy Jr., who oversees the CDC, is a long-time vaccine skeptic.

"It is disappointing that CDC is quiet given that flu kills of hundreds of kids a year and can result in tens of thousands of hospitalizations and tens of thousands of deaths," says Dr. Demetre Daskalakis, who resigned last year as the director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention to protest what he called political interference at the agency.

The CDC declined to make an official available to NPR for this story. In a statement, a CDC spokesperson said, "CDC is developing a communications strategy to provide clear, accessible information about influenza vaccination and other critical steps people can take to protect themselves during respiratory virus season. This includes information about the benefits and risks of vaccination to support informed decision-making."
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