But this time, computer models accurately showed that the storm would make a turn northward, missing the towering glass condominiums of Miami and opulent golden ballroom of Mar-a-Lago in Palm Beach.

Emergency managers had confidence in the National Hurricane Center’s forecast, in part because we’ve gotten used to the idea that weather forecasts are getting more accurate over time, thanks to investments in computing power, observation systems and more.

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But that might not be the case for much longer, scientists and officials warn. A botched rollout of 5G technology, intended to revolutionize the way we communicate and usher in a new era of innovation, could paradoxically roll back some of these forecasting gains.

In a letter Monday to the chairman of the Federal Communications Commission, the chairwoman of the House Science, Space and Technology Committee, Rep. Eddie Bernice Johnson (D-Tex.), expresses concern that we’re headed for such a scenario because of the potential interference of planned urban 5G networks with existing weather satellite sensors. The sensors, mounted aboard polar-orbiting satellites, are used to discern the presence and properties of water vapor in Earth’s atmosphere.

The letter, addressed to FCC Chairman Ajit Pai, calls for the FCC to provide the scientific evidence it is using to inform the commission’s negotiating position ahead of a key international telecommunications meeting. Johnson is seeking the information by Oct. 7 for the committee to review before the start of that meeting Oct. 28.

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“It is imperative that U.S. federal agencies resolve this disagreement about out-of-band emission limits before we begin negotiations with international partners,” the letter states, referring to the limits that describe the amount of noise that 5G devices could be permitted to emit beyond 24 gigahertz.

The letter also, for the first time, releases two reports produced in the past year: one by NASA on behalf of the National Oceanic and Atmospheric Administration, which operates satellites and contains the National Weather Service, and another by NOAA itself.

These highly technical analyses concluded that if deployed widely and without adequate restrictions, telecommunications equipment operating in the 24 GHz frequency band would bleed into the frequencies that NOAA and NASA satellite sensors also use, significantly interfering with the collection and transmission of critical weather data.

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The NOAA report, for example, warns of a potential loss of 77.4 percent of data coming from microwave sounders mounted on the agency’s polar-orbiting satellites.

This issue has been percolating in scientific and communications policy circles for months but will come to a head in late October, when nations gather for the World Radiocommunications Conference in Egypt. That is when countries will agree to guidelines governing the use of the 24 GHz band of spectrum, which the FCC auctioned off for about $2 billion beginning this past March.

That auction went forward despite the warnings of NOAA and NASA leadership and the objection of the Commerce Department, NOAA’s parent agency, as well as the concerns of some on Capitol Hill.

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Instead, after a breakdown in interagency negotiations, political leaders at the White House sided with the FCC and telecommunications industry in allowing the wireless spectrum auction to proceed, according to multiple people familiar with the process, dismissing the possible implications for weather forecasts.

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The Trump administration is pushing for the United States to be a leader in 5G technologies, which has put pressure on science agencies to avoid getting in the way of a major administration priority.

Introducing forecast blind spots

The most important data that goes into computer models used for weather forecasting comes from microwave sounders. Any degradation of this data could harm forecast accuracy. The data is especially useful for making extended forecasts on the order of five to seven days in advance and allows measurements to be taken across regions that have no surface-weather stations, such as the oceans or remote land regions.

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The key concerns about 5G interference focus on what are known as baseline interference limits, often referred to as out-of-band emission limits.

NOAA’s microwave sounders operate at a frequency of 23.6 to 24 GHz, which is close to the frequency that the FCC auctioned off. NOAA favors a strict interference limit, meaning that 5G devices would not be allowed to transmit at frequencies that overlap significantly with the sounders. The FCC and wireless industry favor a looser limit. The meeting in Egypt will determine what the interference limit will be, with the State Department taking the lead in negotiations.

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On May 16, acting NOAA administrator Neil Jacobs testified before Congress that if the interference levels favored by the FCC were to go forward, weather forecast skill would degrade to 1980 levels, when accuracy was 30 percent of what it is today.

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The European Center for Medium Range Weather Forecasts, which operates the world’s top weather model, has also warned of a deterioration in its forecasts if the interference limits don’t adequately protect the satellite frequencies. Such a deterioration could mean billions in economic damages from unanticipated storms and an uptick in weather-related fatalities. It could also harm U.S. national security by reducing the Defense Department’s forecast capabilities.

The FCC and telecommunications industry, for their part, have maintained that the studies from NOAA and NASA — and these agencies’ warnings of a potential forecast apocalypse — are blown out of proportion and based on incorrect assumptions of how the 5G networks would be deployed.

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Although the FCC has advocated for a less restrictive interference limit, it has not produced technical research of its own to justify it. The Science Committee’s letter sent Monday requests that the FCC turn over such research to back up its preferred limit.

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Some lawmakers, such as Sen. Maria Cantwell (D-Wash.), have tried to bring attention to the looming spectrum challenge and fundamental disagreements between scientists at NOAA and NASA and the position of other agencies.

Under questioning from Cantwell at a July 17 hearing of the Senate Commerce, Science and Transportation Committee, NASA Administrator James Bridenstine expressed concern about data loss caused by 5G interference. “I can tell you that depending on the decibel level in that 23.6 gigahertz, we could lose significant data,” Bridenstine said. “If that were to happen, it would affect our ability to predict weather, without question.”

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This answer stands in contrast to what Pai told the same committee a month earlier. When Sen. Ron Johnson (R-Wis.) asked Pai whether there is “any validity or legitimacy” to the concerns raised in the science agencies’ reports, Pai said definitively, “No, absolutely not.”

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Although the baseline interference limit will be decided upon in Egypt, there are growing indications the meeting won’t be the end of the story.

Contingency planning

New legislative language in a proposed Senate appropriations bill, for example, would direct NOAA to conduct a new study on the radio interference issue, including a focus on the financial implications of 5G-related interference. Unlike with the previous reports, which were circulated only to a select few in the executive branch and Capitol Hill, the bill would require NOAA to publicly release its new data.

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The deployment of the 24 GHz 5G technology is several years away, so rather than be caught flat-footed, forecast agencies are planning for various outcomes. They’re betting that telecom companies might be amenable to working with NOAA, NASA and other agencies to make sure that as they activate their networks, they don’t degrade forecasts.

The industry’s sprawling, high-tech infrastructure is hugely vulnerable to severe weather, so if forecasting suffers, these companies will, too. For example, the first thing that people seek to have restored after a storm, in addition to electricity, are phone and Internet networks, and such repairs are costly.

“They would be completely out of their minds with deploying this stuff and screwing up the forecast because so much of their industry is weather sensitive,” said a senior government official who spoke on the condition of anonymity to discuss a sensitive issue that the person wasn’t authorized to discuss publicly.

However, this official noted, as of now, there is nothing that would require communications companies to take steps to mitigate the risk to satellite sensors. That could come in the form of an FCC regulation or congressional legislation, which science agencies such as NOAA and NASA will work toward after the meeting in Egypt, the official said.

In case forecasts are degraded, NOAA is considering plans to avoid the worst-case scenario, which involves the loss of at least 30 percent of overall forecast skill. For example, it could use water-vapor-sensing channels only over oceans and exclude land, which would be the likely source of interference. The loss of only land data would lead to a potential 3 percent degradation in forecast skill, according to experts familiar with the matter.

This may sound small, but its significance becomes clear when one considers that the United States spends about $3.2 billion for every 1 percent increase in forecast skill. This means that the auctioning off of about $2 billion worth of 5G radio spectrum may ultimately set back weather forecasting by about $9 billion, strictly in terms of the investment put into forecasting.

Another option would be to develop artificial intelligence approaches to recover lost or corrupted data from the microwave sounders, much as NOAA did when there was a satellite sensor that malfunctioned in 2018.