BOISE COUNTY, Idaho — The Idaho Transportation Department is reporting the worst conditions they've seen in nearly a decade on a large stretch of Idaho Highway 55.

Dangerous winds and drifting snow in the mountains on the road are so unsafe for plow crews that ITD closed the highway from Banks to Donnelly Monday night. The stretch is more than 50 miles long. 

It's a rare move and ITD is trying to open Highway 55 as soon as it's safe and possible to do so, but for now, they advise travelers not to drive in that area.

RELATED: Idaho 55 reopened between Banks and Donnelly

In the Treasure Valley, Monday morning flakes flew and stuck around for a bit. But it's the mountains where snow is piling up, with snow banks reaching four feet tall.

A KTVB crew rode along with an ITD snow plow operator based out of Boise and meandered up to the mountains on Highway 21.

"Us valley guys, we like coming up here,” Scott Wenger, an ITD transportation maintenance worker, said. “It’s been pretty slow so far for us in the valley. We've had a couple storms (here).”

Plow operators have to be cautious and not get too close to the edge of Highway 21 because there’s not much shoulder room, and the creek is just feet down from the side of the road. The same can be said about Idaho Highway 55 in some areas.

RELATED: KTVB Road Reports

“This area isn't our area but we will go up and help,” Wenger said. “Up here obviously they're going to be busy keeping the roads open.”

Highway 21 and mountain towns up in that direction are getting pummeled with snow. Fortunately that highway is still open, thanks to plow operators doing diligent work throughout the day.

“It can ice up, you don't want it to ice up when temperatures get cold so we want to get it off the road,” Wenger added.

Wenger says plow operators have to keep speeds low when plowing and putting down material.

“We have to go under 45 miles an hour when putting material out...plowing faster than 45 it doesn’t really help,” he added.

Meanwhile, valley crews are watching this week's frosty forecast like hawks, gearing up and preparing for the next storm.

“Prior to a storm coming we try to pre-treat, pre-treating with salt or [magnesium chloride] so that when it does snow hopefully it melts off. And then if it really snows we have to get out and push it off,” Wenger said.

If it dumps hard enough, travelers will see all hands on deck, 24 hours a day.

Wenger says at times drivers will try to go around plows to get ahead, but that can be dangerous when roads are sketchy.

Some tips: slow down, give yourself more time to get where you're going and leave a good following distance so you have more time to react if something happens.