After roughly two decades, NOAA has shut down the North American Mesoscale model, known to forecasters as the NAM, a computer model with a reputation for overhyping storms.

The NAM, which began running around 2005, produced forecasts up to 84 hours out and was used mainly for localized precipitation events. It tended to overpredict, especially during hurricane season. It often showed a cyclone’s central pressure far lower than reality, which suggested a much stronger storm. Being off by a category or two can mean a big difference in projected damage.

Because meteorologists have so many tools, they often treated the NAM as an outlier. Its dramatic runs, whether a “snowmaggedon” or a record hurricane that never materialized, regularly stirred up social media. Users may see fewer alarming posts now.

Florida Public Radio Emergency Network meteorologist Audrey Shirley said she used the NAM daily throughout her career, even though it exaggerated rainfall and cloud cover. “It’s more of a sentimental loss for me,” she said.

Forecasters kept the model for so long because it filled gaps larger models sometimes missed, especially with winter weather. It performed well along the Appalachians and the I-95 corridor. In Florida, however, summer sea-breeze thunderstorms and tropical systems proved harder for it to handle.

The Rapid Refresh Forecast System replaces it. The NAM updated about four times a day, while the new system produces output every hour using radar, observations, and satellite data.

Meteorologists say the loss does not hinder forecasting, since dozens of other models, including artificial intelligence systems, remain available. NOAA’s National Centers for Environmental Prediction said the move, along with the retirement of several other short-range products, is part of a broader modernization effort.

Follow the St. Pete-Clearwater Sun on Facebook, Google, & X

St. Pete-Clearwater Sun: local St. Pete-Clearwater & Tampa Bay, FL news at PIE-Sun.com