The JPSS-1 satellite is scheduled to launch Nov. 14. (Ball Aerospace & Technologies)

Weather forecasts are getting better, perhaps contrary to popular belief. In fewer than two decades, the accuracy of a five-day forecast has improved to what used to be the three-day forecast. Even seven-day forecasts today are just as accurate, if not more accurate, than a five-day forecast in the 1990s.

Some of the improvement can be traced to better and faster computers. Researchers have come up with more advanced ways of connecting the physics of the atmosphere via algorithms and, more importantly, computers themselves have become more advanced.

But that’s just a small part of the reason you get a better prediction of whether it’s going to rain on your outdoor wedding. The big change has been in the data, the vast majority of which come from a special kind of satellite.

“The models are getting better, yes,” says Mitch Goldberg, who is eagerly anticipating the launch of NOAA’s next polar-orbiting satellite. “But we’re also getting more data. And the data itself is improving.”

Goldberg is the program scientist for the Joint Polar Satellite System project, which — barring delay — is scheduled to launch its first satellite from Vandenberg Air Force Base in California on Tuesday at 1:45 a.m. Pacific time.

Ball Aerospace engineers and technicians perform final checks on JPSS-1 in the clean room. (Ball Aerospace & Technologies)

“The most critical data in forecast models comes from polar orbiting satellites because they collect observations globally,” Goldberg told The Washington Post. That’s because “a disturbance thousands of miles away can become a major event three to seven days later” in our part of the world.

Not only is the data the most critical, it’s nearly all of the data that feeds the global forecast models. That, Goldberg says, is why it’s so important to keep that fleet of satellites in tiptop shape. JPSS-1, which after launch will be called NOAA-20, is the next generation of the polar-orbiting fleet. And it’s got a new data processing system that will integrate the data twice as fast.

The launch comes at a critical time, because the current fleet is at the end of its “design lifetime,” meaning the satellites weren’t necessarily built to live much longer than this. Satellites outlast their life expectancy all the time, but the risk of failure increases markedly from here on out.

“It’s like driving a car with 200,000 miles to Florida,” Goldberg said. “Sure you might be able to do it, but would you want to? You can’t take that risk.”

For years, the weather community — including NOAA — has been concerned that a gap in our satellite coverage could lead to severe forecast degradation. The JPSS project has been criticized for “mismanagement, billions in cost overruns and technical development challenges.”

NOAA even went as far as to ask the community for a list of contingency options should a polar-orbiting satellite fail before JPSS-1 is launched.

This is because 85 percent of the global forecast model input comes from polar-orbiting satellites. If you need quantifiable proof that removing 85 percent of the models’ data would result in terrible forecasts, the scientists who run the European model did that study after Hurricane Sandy. Without this data, we wouldn’t have known Sandy was going to make landfall — let alone in the nation’s most populous region.

The community is breathing a sigh of relief now that JPSS-1 is ready to launch, with three more carbon copies in the production line.

The VIIRS sensor for JPSS-2 comes out of thermal vacuum chamber testing at Raytheon. (Reuben Wu/Raytheon)

The new series collects data on temperature, air moisture, ice, snow and precipitation. It has a nifty instrument that uses light from the moon to create day-like images of weather, even where it’s dark. The instruments can help map regions that are flooded, like in Houston after Hurricane Harvey, and they can see the extent of power outages, such as in Florida after Hurricane Irma.

All of this will help improve the forecasts that people and the economy as a whole rely on, Goldberg says.

“Twenty years ago, it was like flipping a coin,” he said of the now-common seven-day forecast. “TV meteorologists would never even show a seven-day forecast back then.”

Now we have a pretty good idea of what the weather will be like next week, in no small part because of satellites like JPSS.