Mount Roundtop mountain forecast

Summit

6,138 ft (1,871 m)

Forecast grid ground

3,806 ft (1,160 m)

Summit temperature

33°F

Summit wind

SW 47 mph

Freezing level

6,483 ft

High at the summit, by lapse rate

28°F

The last tile carries the Weather Service’s high from its grid’s 3,806 ft up 2,332 ft to the summit at the standard atmosphere’s 6.5 °C per kilometer (about 3.6 °F per 1,000 ft). Real lapse rates vary: an inversion can make the summit warmer than the valley.

NOAA’s GFS model, run Fri, Sep 25, 4:00 PM AKDT, interpolated to 6,138 ft between its pressure levels: the free air over the summit, which on a ridge is close to what a climber feels and in a sheltered spot is more than it. Wind chill is the National Weather Service’s formula, given where the temperature is 50°F or less and the wind above 3 mph.

The Weather Service’s forecast asked at the summit’s coordinates (54.7994, -163.5912), by its office in Anchorage West. Its grid cell is 2.5 km across and sits at 3,806 ft (1,160 m), 2,332 ft below the summit, so its temperatures and winds are for that height.

An estimate: the height a rising parcel of the grid’s air would reach saturation, about 125 m for every degree Celsius between temperature and dew point (Espy’s rule), added to the grid’s ground. It fits cumulus and fog made on the spot, not a deck of stratus carried in from elsewhere.

September 26: 0.5 in · September 27: 2.1 in · September 28: 0.7 in · September 29: 0.4 in · September 30: 1.0 in · October 1: 1.4 in. 6.1 inches in all.

National Weather Service snowfall at the grid cell over the summit.

For a sea-level horizon at the summit’s position, local time. From a summit the horizon sits lower, so the sun is seen a few minutes before sunrise and after sunset; a ridge to the east or west does the opposite.

Why a summit forecast differs

The air cools with height, by about 3.6°F per 1,000 feet on average, and the wind above a ridge blows at the speed of the free atmosphere rather than slowed by the valley floor. A town’s forecast says little about the top of the mountain above it.

Freezing level

The height where the air is at 32°F (0°C). Above it precipitation falls as snow and wet rock freezes; the snow line usually sits a few hundred to a thousand feet below it.

Wind chill

How cold the air feels on exposed skin, from the temperature and the wind, by the National Weather Service’s 2001 formula.

Cloud base

Where cloud begins. When it is below the summit, the top is in cloud: no view, and in cold air, rime ice and poor visibility.

Prominence

How far a summit rises above the lowest contour line that encircles it and no higher summit: the measure of a mountain’s own height, not its neighbors’.

Summits

• Isanotski Peaks8,107 ft · 6 mi
• Mount Shishaldin9,373 ft · 15 mi
• Amak Volcano1,601 ft · 46 mi
• Mount Westdahl5,427 ft · 47 mi

Forecasts from the National Weather Service. Summit-height temperature, wind and freezing level from NOAA’s Global Forecast System on NOAA Open Data. Summits from Wikidata (CC0): prominence >= 600 m, or elevation >= 4267 m, or >= 12 Wikipedia editions; English Wikipedia article required; read 2026-09-25. Mountain weather changes fast; check the forecast again before you go.