|May 14, 2010 at Hebgen Lake.|
Ice-out depends on a number of factors; it's not quite as simple as ice peeling off uniformly as you go up. The factors include recent weather, the prior winter's weather and snowpack, exposure to the sun, the amount of water flowing through via inlets and outlets, and of course the lake's elevation. For example, note in the list below how Hebgen Lake at about 6,500 feet actually tends to ice-out two or three weeks before nearby Cliff and Wade Lakes, which are at about 6,250 feet. My guess is that this is due to the fact that Hebgen has a good push of water flowing through via the Madison River, while Cliff and Wade have small insignificant tributaries and outflows (both get adequate sunlight and would have had similar weather).
One way to get a rough idea if the mountain lake you have in mind might have iced-out is to drive to a lake like Hebgen Lake or Hyalite Reservoir. It will at least give you an idea about other lakes at that elevation, and you can estimate uphill from there. Very approximately, ice out ascends about 5,000 feet every couple of weeks.
|May 20, 2008 at Hyalite Reservoir.|
From earliest to latest:
- Hebgen Lake (about 6,500 feet): End of April-Early May
- Cliff and Wade Lakes (about 6,250 feet): Mid-May*
- Hyalite Reservoir (about 6,700 feet): Mid-late May
- Yellowstone Lake (about 7,800 feet): May 20-ish.
- Pioneer Mountains at 7,500 feet: June 1
- Pioneer Mountains at 8,000 feet: June 10
- Bell Lake (about 8,750 feet, Tobacco Roots): Mid-June
- Pioneer Mountains at 8,500: June 20
- Gneiss Lake (9,554 feet, Tobacco Roots): July 1
- Pioneer Mountains at 9,000 feet: July 1
- Twin Lakes (about 8,200 feet, North Meadow Creek in the Tobacco Roots): Early-mid July, though this might be an anomaly
- Pioneer Mountains at 9,200 feet: July 10
*Heard a report this year of Wade Lake being ice-free on May 3.