How Cold Will It Feel at the Summit?
The temperature on your car's dashboard is the least useful number of your hiking day. Between the trailhead and the summit stand two multipliers mountains never waive: altitude strips degrees as you climb, and ridgeline wind cuts through whatever is left.
Enter the trailhead temperature, expected wind, and the elevations of your start and high point. This tool projects the summit air temperature, computes the felt temperature with the official wind-chill standard, and reads out the frostbite risk band — before you commit to the climb.
Check summit conditions
- Summit air temperature
- 19°F
- Cooling from altitude alone
- −16°F
Feels like at the summit
4°F
wind chill, NWS/Environment Canada standard
Frostbite risk: Moderate — frostbite possible in ~30 min
Cover exposed skin, pack windproof layers, and plan short summit stops. Turn around if conditions worsen — summits are optional, returning is not.
How this is calculated
Summit temperature is projected with the International Standard Atmosphere lapse rate of 6.5 °C per 1,000 m. Real conditions vary — temperature inversions can flip the gradient in calm winter high-pressure — but for planning purposes the standard rate is the accepted baseline.
The felt temperature uses the JAG/TI wind-chill formulaadopted jointly by the US National Weather Service and Environment Canada in 2001, derived from clinical trials of heat loss from bare skin in a wind tunnel: WC = 13.12 + 0.6215·T − 11.37·v0.16 + 0.3965·T·v0.16 (T in °C, v in km/h). It is valid for temperatures at or below 10 °C and wind of at least 4.8 km/h; outside that range the tool reports plain air temperature.
Frostbite bands follow the Environment Canada chart: risk becomes meaningful below −10 °C wind chill (≈30 min to freeze exposed skin), serious below −28 °C (≈10 min), and critical below −40 °C (≈5 min).
Frequently asked questions
Why is it so much colder at the summit than the trailhead?
Air cools about 6.5 °C for every 1,000 m you climb (3.5 °F per 1,000 ft) — the standard atmospheric lapse rate. Climb 1,500 m and a pleasant 15 °C trailhead becomes 5 °C before wind is even considered. Add exposed-ridge wind and the felt temperature can drop below freezing on a sunny autumn day.
What wind speed should I enter?
Use the forecast for the summit or ridgeline, not the valley — mountain forecasts (NOAA point forecasts, mountain-forecast.com) publish these. If you only have a valley forecast, expect roughly 1.5–2× that speed on exposed ridges.
Why does the tool sometimes say wind chill "not applicable"?
The standard formula is only valid at or below 10 °C with wind of at least 4.8 km/h — outside that envelope, the concept loses physical meaning and the tool reports plain air temperature instead. That honesty matters: a fabricated number in warm weather would be noise.
How reliable is the frostbite time?
The bands come from Environment Canada's wind-chill chart and assume exposed skin. Gloves, a balaclava, and windproof layers extend those times dramatically — the number is your cue for how seriously to cover up, not a countdown you can safely run to zero.
Does this replace checking a mountain forecast?
No — it translates a forecast into what your skin will feel. Always check a summit-specific forecast for wind, precipitation, and freezing level, then use this tool to decide on layers, exposed-skin coverage, and how long to linger on top.