Days of rain and a sharp cooldown will swamp weekend outdoor plans across Northwest Montana, with accumulating snow possible in the mountains.

Showers will transition to steady rain Friday. Temperatures over the weekend will top out in the 50s and low 60s in valley locations, with overnight lows in the 40s.

Terrain above 6,000 feet could see wet, heavy snow, the National Weather Service in Missoula warned in its Thursday forecast.

“A cold front will sweep across the region causing a drastic change in the weather pattern,” the forecast said. “It will start with thunderstorms, but behind the front the snow levels will fall and we can expect to see some snow falling by Sunday morning in the Anaconda-Pintlar, Sapphire and Bitterroot mountains, as well as along the Continental Divide.”

A winter storm watch was issued for the Bitterroot Mountains along the Montana-Idaho border, where up to 8 inches of snow could fall.

The dreary, cold forecast could linger through at least Tuesday.

Northwest Montana and Glacier National Park are expected to see the heaviest precipitation early next week.

“Late Sunday into Tuesday will be the toughest conditions up there,” the Weather Service forecast said. “If you’re out recreating on any small streams and rivers, be prepared for rapidly changing flows and much cooler temperatures.”

Recreationists were advised to plan for winterlike conditions in the backcountry.

The Flathead River at Columbia Falls was predicted to rise about a foot by Tuesday to 8.6 feet. The Swan River at Bigfork could also jump up a foot to 4.8 feet.