Dallas winter weather: What is lake-effect snow?

Days before the arctic front arrived, meteorologists waffled back and forth whether North Texas would get any snow. If the region did get any, they agreed, there would be little to no accumulation.

North Texas instead woke Monday to a sold layer of snow, with reports ranging from just a half-inch to 2 inches in some places.

So what happened? You can blame — or thank, depending on your point of view — something called lake-effect snow for the snowy surprise.

Lake-effect snow is common around the Great Lakes or other regions with large lakes, but not in Texas, where lakes tend to run small, said Madi Gordon, a meteorologist with the National Weather Service in Fort Worth.

The weather phenomenon occurs when cold, dry air passes over warm lake water, transferring warmth and moisture into the atmosphere. The air rises, forming clouds that grow into narrow bands and produce snow.

Lake-effect snow is difficult to predict because it occurs on such a local scale, Gordon said, with wind direction and physical geography of the land and water playing major roles.

“Heavy snow may be falling in one location, while the sun may be shining just a mile or two away in either direction, the National Weather Service explained.

Lakes across North Texas contributed to the effect, with bands appearing at Lewisville, Grapevine and Ray Roberts lakes and Lake Tawakoni, about 50 miles east of Dallas. As of early afternoon Monday, the heaviest snowfall report was 2.25 inches in Coppell, just south of Lewisville Lake, according to the weather service.

Much of the snow is expected to melt Monday with a mixture of sun and vehicle traffic, but compacted snow will refreeze Monday night, likely leaving behind ice, said Juan Hernandez, a weather service meteorologist.

Drivers should expect a “sub-optimal” Tuesday morning commute, he said.