Some self-realization may save your life as a major fall snowstorm rolls through central and southern Wyoming today and Thursday.

"If things are bad, ask yourself if the trip is necessary," said Doug McGee, spokesman for the Wyoming Department of Transportation.

Motorists should think hard before driving as snow will pile up to 12 to 18 inches in southwestern Wyoming and along the Interstate 80 corridor, and to nearly a foot in central Wyoming by the time it leaves the state , McGee said.

"Know before you go," he said.

Know this, too.

"It's going to be a pretty impressive storm," said meteorologist Roger Smith of the Riverton office of the National Weather Service.

Wyoming will contend with two storm systems, Smith said.

One storm system is coming from the southwest and will cause near blizzard conditions in Sweetwater counties eastward to Laramie County, according to the National Weather Service. A blizzard is a weather condition marked by sustained 35 mph winds and visibility less that one-quarter of a mile.

The other storm system is coming from Canada and will bring its own wind and snow, Smith said.

On Tuesday afternoon, the National Weather Service issued winter storm warnings for Natrona, Converse, Platte, Goshen, Laramie, Albany, Carbon, and Sweetwater counties. Winter storm warnings also were issued for portions of Fremont and Sublette counties along the Continental Divide. A winter storm warning means severe winter weather conditions are expected or occurring. Significant amounts of snow are forecast that will make travel dangerous.

Many of these winter storm warnings will continue through Thursday morning, but those in southeastern Wyoming will not end until 6 p.m. Thursday.

Temperatures will stay mostly in the 20s.

This morning, snowfall probably will amount to several inches in the Casper area north to the Big Horn mountains.

But Laramie and Albany counties will receive that and more.

"The Interstate 80 corridor will be highly impacted," Smith said.

The snow will be relatively dry, which is easy to shovel but bad news for motorists especially with the winds, he said.

Sustained winds across central and southern Wyoming will increase to 20-25 mph with gusts up to 35 mph, and in some places those sustained winds will exceed 40 mph with gusts up to 55 mph, according to the National Weather Service.

Those conditions will challenge WYDOT plowing crews that will do battle with the storm along I-80 and I-25, and other state roads, McGee said.

He urged motorists to help themselves by helping WYDOT do its job.

The plow and sanding trucks kick around a lot of snow, reducing visibility to near zero, McGee said.

If motorists see such a cloud, they should keep their distance because there's probably a truck causing it, he said.

They should keep their distance, too, if they value their vehicles' windshields and paint, McGee said. "The sand we're spreading is not playground sand."

Drivers should not attempt to pass the trucks unless they have a clear area, and they should never pass them on the right because the blades extend beyond the width of the plow trucks, he said.

WYDOT crew foremen close highways on a case-by-case basis, and do so usually to bring out the heavy clearing equipment and in rare cases because the conditions are so bad that plow drivers can't make it, McGee said.

And when they do it, they mean it, he said. "Never, ever run a road closure gate."

Reach Tom Morton at (307) 266-0592, or at tom.morton@trib.com.