Take 24-below-zero forecast with a grain of (road) salt

People who swiped open their weather app Tuesday morning were met with a bone-chilling Spokane temperature outlook for late next week: 24 below zero.

But the National Weather Service in Spokane says that’s likely not accurate.

The weather service issues seven-day forecasts based on a blend of different weather models, said Rocco Pelatti, meteorologist at the Spokane branch.

“We use an ensemble forecast,” he said.

Meteorologists have a number of different models to predict what weather systems will do. Each model has its strengths and weaknesses so using a blended model results in an average forecast, he explained.

“The downside of that though is sometimes you can lose the fine details,” Pelatti said.

So meteorologists will look at some of those individual models and take them into consideration, too. All weather modeling though, tends to lose reliability the further out it gets, Pelatti said.

“The farther out you go the bigger the error is and the more uncertainty,” Pelatti said.

That’s why the National Weather Service issues seven-day forecasts, he explained.

Many apps though will use a singular model for their 10-day forecasts, showing a more extreme outcome, Pelatti said.

Hence the prediction of minus 24 for a week from Thursday. Within hours the popular weather apps on smartphones had moderated, with lows at 8 below zero – still bitter cold, but not Antarctica cold.

“That’s what I believe you’re seeing, (when) a deterministic model runs that far out, are the extremes,” Pelatti said.

A new weather system is moving into the Spokane area Wednesday that might bring some flurries of snow but is largely dry, Pelatti said.

That weather system will be pushed out with a northerly flow bringing lower temperatures and ultimately turning into an “artic front” over the weekend, Pelatti said.

On Monday, Pelatti forecasts a low of four degrees and a high of 14.