* WHAT...Heavy snow. Total snow accumulations between 12 and 18 inches and up to 24 inches along the western slopes of the Tetons. 6 to 10 inches of total snow accumulation is expected in Yellowstone National Park, with amounts up to 18 inches along higher elevations across southern portions of the park. The Mammoth area will see 1 to 3 inches. Winds could gust as high as 45 mph. * WHERE...Teton and Gros Ventre Mountains and Yellowstone National Park. * WHEN...Until 6 PM MDT Friday. * IMPACTS...Travel could be very difficult, including over Teton Pass and Togwotee Pass.

* WHAT...Heavy snow expected. Total snow accumulations between 6 and 12 inches, with amounts approaching 20 inches above 7500 feet in the Gallatin and Madison Ranges. Winds gusting as high as 40 mph will create areas of blowing and drifting snow Thursday night. * WHERE...Little Belt and Highwood Mountains and Gallatin and Madison County Mountains and Centennial Mountains. * WHEN...Until noon MDT Friday. * IMPACTS...Travel could be very difficult and tire chains may be required for some vehicles. Those in the backcountry should ensure they are prepared for dangerous conditions. * ADDITIONAL DETAILS...Snow accumulations on road surfaces may be limited through the afternoon hours, with impacts to travel increasing from this evening and through the morning hours on Friday as snow accumulates on roads and blowing snow reduces visibility.