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D-FW's surprise snowfall shows difficulty of forecasting

Friday turned out to be a record-setting snow day -- and a challenge for North Texas weather forecasters, who say snowfall is one of the most difficult kinds of weather to accurately predict.

On Thursday, the forecasts called for Tarrant County to get a trace to 2 inches of snow beginning before dawn Friday.

Instead, the snow began falling late Thursday. By noon Friday, 2.6 inches had been recorded at Dallas/Fort Worth Airport, easily surpassing the previous record, 0.1 inch, set in 1989.

And even though only 0.2 inch of snow fell before midnight Thursday, that was enough to tie the Feb. 3 record, set in 1956.

For the total "snow event," other parts of North Texas got 3 to 7 inches, or "about 2 to 21/2 times what we first expected," said David Finfrock, KXAS/Channel 5's chief meteorologist.

Being off the mark on snowfall predictions is not unusual.

Last year, meteorologists with the National Weather Service and TV stations predicted that the Fort Worth area would get 1 to 3 inches of snow on Feb. 11. Instead, a record 11.2 inches fell.

On Thursday, "for most of the area, the forecast was right," said meteorologist Matt Mosier with the National Weather Service in Fort Worth. "For areas in Waco, Temple, Killeen and areas west of I-35, we got the expected snowfall amounts."

But in North Texas, the low-pressure system that moved in from the south was stronger, began producing snow earlier and lasted longer than expected.

"We all knew it was going to be snow and a very dry air mass," Finfrock said. "This time it was a dry, powdery snow, and that's unusual."

Mosier said that because of the difficulty in forecasting snow, "you see larger ranges in forecasts, like 2 to 4 inches, than in rainfall. We can predict rainfall more precisely than snowfall and would never put that much of a range in a forecast for rainfall."

The atmosphere and the ground temperatures must both be cold enough to encourage snow, and since North Texas had been below 25 degrees for days, snow accumulated right away, Mosier said.

"We thought it would take it longer to generate snow than it did," he said. "We thought that up here in the Metroplex, it would be too dry."

Snow's liquid-to-solid ratio can also make a difference in the measurements, Finfrock said, and North Texans tend to pay extra attention to snowfall figures.

"If you predict 1 inch of rain, and it's 11/2 inches, people don't think anything of that," he said.

Meteorologists base their forecasts on three major national models that have been used for a long time, along with regional and local models that can refine the outlook, Mosier said.

"We have no shortage of things to look at," he said. "Then we use current observations and our own knowledge to make a forecast."

The system's location was "very well-forecast" by the models, Mosier said, but the snowfall predictions were, well, all over the map.

"Even on Thursday, you had a range from no snowfall at all to 6 to 7 inches," he said.

Shirley Jinkins, 817-390-7657

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