Mountain Weather

15-day summit forecast

Choose a mountain and see everything you need for your climb on one page.

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Forecast reliability

Days 1–3 highDays 4–7 mediumDays 8–15 low

Important: Use the later days to see the general trend, not for firm plans. This is a general guide: local storms in the mountains can develop differently than expected even in the first days.

Temperature colours

−30°0°+25°

How is it calculated?

Temperatures by altitude and summit wind are interpolated from model data for different pressure levels of the atmosphere. Red wind means more than 60 km/h; a red freezing level means melting above the summit. Cloud base and visibility by altitude are estimated from the relative humidity of the layers; details below.

Source

Weather data: Open-Meteo (CC BY 4.0). This is a model forecast; always check official warnings and local conditions before going into the mountains.

How to read the table

Columns show the days, and rows show the conditions a climber will meet on the way. The forecast for the first three days is fairly reliable; from day 8 onwards it only shows the general trend.

Freezing level: the altitude at which the air is at 0 °C. The upper figure is the day’s highest value and the lower figure the lowest. If it is red, there may be melting even at the summit; snow bridges and glacier crossings get weaker.
Summit wind: the strongest hourly wind of the day. Above 40 km/h is yellow and above 60 km/h is red; at these speeds ridge and summit crossings become difficult and can be dangerous. The colours are a warning, not a hard limit. The value in the table is an hourly average; gusts can be stronger.
Summit feels like: the lowest feels-like temperature, calculated with the wind chill formula. Check this value for the risk of frostbite.

Cloud base

The cloud base is the lowest altitude at which cloud begins. It is calculated from the relative humidity in different layers of the atmosphere: the first altitude above the model surface where humidity reaches 95% is taken as the cloud base. This is an approximate estimate from model data, and the real cloud base may differ by a few hundred metres. The table shows the lowest base during daytime hours (06–18) and the number of cloudy hours. If the base is below the summit, the value is marked in yellow: part of the climb may be in cloud. “None” means no cloud is expected during the day.

Important: this is an estimate. The model layers are a few hundred metres apart and may not fully capture local clouds that the mountain creates itself (slope fog, afternoon cumulus build-ups).

Visibility

The Visibility row is the visibility the model calculates at the surface (at the model elevation given in the table); the lowest daytime value is shown in kilometres. Below 5 km is yellow and below 1 km red.

No direct visibility forecast is published for the summit and intermediate altitudes. So the Visibility by altitude section shows how much of the daytime each altitude will spend in cloud. Inside cloud, visibility often drops below 1 km, and below 100 m in thick cloud; finding your way gets hard and a whiteout can develop.

Good: that altitude is out of cloud for most of the daytime.
Variable: it may be in cloud for a few hours during the day.
<1 km: more than half of the daytime is spent in cloud.

Mountain meteorology in brief

A flowering meadow in front of snow-covered Mount Rainier — Flowering meadow and the snowy summit of Rainier · Photo: NPS

01 / 20

0.65 °C every 100 metres

As you climb, the air cools by about 0.65 °C every 100 metres on average; in dry air the difference approaches 1 °C. If it is 15 °C in the valley, expect about 5 °C on a summit 1,500 m higher. The temperatures by altitude in the table show this difference.

Source: Weather Glossary: L, NOAA JetStream

Snow blown off a snowy ridge by strong wind — Snow blowing off a ridge: strong wind at the summit · Photo: Kefi

02 / 20

Wind chill

Wind strips away the layer of warm air around the body, so the skin cools much faster. Air at −10 °C with a 40 km/h wind feels like −21 °C. The “Summit feels like” row in the table shows this calculation; check this figure for frostbite. It uses the wind chill formula used in the US and Canada since 2001, valid below 10 °C and for wind above 4.8 km/h. Sun, humidity and clothing are not taken into account.

Source: Wind Chill Chart, US National Weather Service (NWS)

Dark storm clouds over the Teton Range and Jackson Lake — Storm clouds over the Teton Range · Photo: Grand Teton NPS

03 / 20

Afternoon storms

On summer mornings the sun warms the slopes, and the warm air rises to build towers of cloud. Cumulus that look like cotton wool in the morning can turn into a thunderstorm with lightning in the afternoon. That is why you should reach the summit and start down before noon.

Source: Lightning Safety in the High Country, Rocky Mountain National Park

Lightning striking over a lake surrounded by mountains — Lightning over Lake Chelan · Photo: NPS

04 / 20

What to do in lightning

If you can hear thunder, you are within reach of lightning. Move away from summits, ridges and isolated rocks. If you are in a group, spread out so that the current cannot pass from one person to another.

Source: Lightning Safety Outdoors, US National Weather Service (NWS)

A lens-shaped cloud above Mount Rainier — Lenticular cloud over Mount Rainier · Photo: Steve Redman, NPS

05 / 20

Lenticular clouds

A cloud that hangs motionless above the summit like a flying saucer forms in the wave of strong wind passing over the mountain. Although the cloud stays in place, air flows through it at tens of kilometres per hour. If you see a lenticular cloud, expect strong wind on the summit.

Source: Altocumulus lenticularis, WMO International Cloud Atlas

A small cap cloud sitting on top of a snowy, pointed summit — A cap cloud sitting on the summit · Photo: NOAA

06 / 20

Cap and banner clouds

As moist air passes over the summit it cools and forms a cloud that sits on top like a cap. A cloud stretching from the summit in the direction the wind blows is a banner cloud. Even if the weather looks calm from below, both tell you there is moisture and strong wind at the summit.

Source: Orographic influences on the windward side, WMO International Cloud Atlas

A halo around the sun with bright spots on either side, above a ski resort — Halo and sun dogs over Deer Valley · Photo: Taigne Hammock

07 / 20

Cirrus and the solar halo

Ice clouds that cover the sky like a thin veil form a ring around the sun. These clouds are often the forerunner of an approaching front; the weather may turn within one or two days. If you see a halo before a planned climb, check the forecast again.

Source: Halo phenomena, WMO International Cloud Atlas

A mountain summit rising above a sea of cloud — Amphitheater Mountain above the clouds · Photo: Yellowstone NPS

08 / 20

Temperature inversion and the sea of cloud

On clear, windless nights cold air sinks into the valleys: the valley stays foggy and cold while the summit is sunny and warmer. From the summit, the valleys lie under a white sea. If the table shows a low cloud base and “good” upper altitudes, you may climb above the sea of cloud.

Source: What is a temperature inversion?, Met Office

A group walking in thick fog on a snow slope marked with route flags — A snow slope with route flags in fog · Photo: NPS

09 / 20

Whiteout

When snow and cloud merge, light comes equally from every direction; shadows, the horizon and the slope disappear. A drop or a cornice one step away cannot be seen. If visibility in the table is red, load the route into your GPS and, if necessary, stop and wait.

Source: Blizzards and snow drifts, Met Office

A climber in heavy clothing on the summit of Everest, with mountains above the clouds behind — A climber on the summit of Everest · Photo: Alfonso.mnr

10 / 20

Snow blindness and UV

UV radiation increases by about 10% for every 1,000 metres of height, and fresh snow reflects up to 80% of it. Unprotected eyes burn after a few hours, causing a gritty feeling and temporary blindness. Wear sunglasses with side protection even on cloudy days.

Source: Radiation: The ultraviolet (UV) index, World Health Organization

An old pocket altimeter with feet and inch scales on its dial — Pocket altimeter · Photo: Slashme

11 / 20

Falling pressure and the altimeter

Altimeters in watches and phones calculate altitude from air pressure; as pressure falls they show you higher than you are. If you are “climbing” at night while lying still in camp, the pressure is falling and the weather may turn. Correct your altimeter at points of known height.

Source: Air Pressure, NOAA JetStream

A sunlit, hard, wind-worked snow slope — A sunlit snow slope · Photo: Kefi

12 / 20

Freezing level and alpine starts

Snow that freezes overnight is firm in the morning and crampons grip well; as the sun rises it softens, snow bridges weaken and rockfall increases. That is why climbs on snowy routes start after midnight. If the lowest freezing level in the table is above the summit, there will be no overnight freeze.

Source: Climb Safely, North Cascades National Park

13 / 20

Foehn wind

Air that has dropped its moisture on the windward slope warms and dries as it descends the other side. This warm, dry wind can raise temperatures quickly within a few hours and melt snow fast. Avalanche risk increases on foehn days.

Source: Foehn effect, Met Office

Hand-drawn diagram of wind blowing up a slope by day and down by night — Daytime and night-time slope winds · Drawing: KVDP

14 / 20

Slope winds

By day, air blows upwards from slopes warmed by the sun. At night, cooling air becomes heavier and flows down into the valley. That is why a camp on the valley floor is the coldest place at night.

Source: Prevailing Winds, US National Weather Service (NWS)

The snow-covered Himalaya seen from space — The Himalaya from space · Photo: NASA

15 / 20

The air thins with height

Air gets thinner as you go up; at about 5,500 m the pressure is half of that at sea level. The air is still 21% oxygen, but each breath brings less oxygen into the lungs. On the summit of Everest it approaches one third of the sea-level amount.

Source: Constant Pressure Charts: 500 mb, NOAA JetStream

A large snow cornice overhanging the edge of a snowy ridge — Snow cornice on the Shuksan Arm · Photo: OrionGeo310

16 / 20

Wind-blown snow and cornices

Wind picks up snow from the ridge and piles it onto sheltered slopes. A hard wind slab forms, along with cornices that overhang the edge of the ridge. Do not step onto a cornice: the fracture line can be much further back on the ridge than you expect.

Source: Cornice Fall, Avalanche.org

Cloud from the sea covering the windward slope of mountains — Cloud covering the windward slope of the mountains · Photo: KpokeJlJla

17 / 20

Wet windward, dry leeward

Moist air hits the mountain, rises, cools and drops its rain or snow on the windward slope. The other side of the mountain lies in a “rain shadow”. This is why the Rize side of the Kaçkar Mountains is foggy and wet while the southern side is drier.

Source: Orographic influences on the windward side, WMO International Cloud Atlas

A low, dark, shelf-shaped wall of cloud on the horizon — Shelf cloud ahead of a cold front · Photo: Erik dos Santos

18 / 20

Cold fronts

As a cold front approaches, pressure falls and a dark, low wall of cloud appears on the horizon. As it passes, the wind shifts and strengthens, the temperature drops by several degrees within a few hours, and showers or snow arrive. Clear, cold weather usually follows.

Source: Understanding weather, Met Office

Trees with branches coated in thick white rime — Rime on trees · Photo: Jim Peaco, NPS

19 / 20

Rime and verglas

Supercooled cloud droplets freeze instantly when they hit rock or trees, forming feathers of rime that grow into the wind. The feathers point to where the wind is coming from. If melting snow or rain freezes on rock, it leaves a thin, clear coat of ice. This ice is hard to see and very slippery to hold.

Source: Weather Glossary: R (rime ice), NOAA JetStream

Stars and the Milky Way above snowy Wheeler Peak — The Milky Way above Wheeler Peak · Photo: NPS

20 / 20

Clear nights are colder

Cloud holds in heat like a blanket; on a clear night the ground’s heat escapes straight into space. So a starry night is noticeably colder than a cloudy one. The coldest moment of the day is just before sunrise.

Source: Weather Glossary: R (radiational cooling), NOAA JetStream