Why is it colder in the mountains?
Because the atmosphere is mostly heated from the ground up, and air cools as it rises and expands. On an average day it gets about 3.5°F colder for every 1,000 feet you climb, so a summit can be 20 to 30°F colder than the valley below.
Show me why1 min
Heated from below
Sunlight passes through the air and warms the ground, and the ground warms the air touching it. Higher up you're farther from that heater. Air that rises also expands as the pressure drops, and expanding air cools, the reverse of the squeezing that heats sinking air in a Santa Ana.
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Thin air, strong sun
Mountain air is thin and dry, so it holds little heat and loses it fast at night. But the same thin air lets more sunlight through, which is why you can sunburn quickly on a cold summit, and why a sunny rock feels warm while the air is cold.
When valleys are colder
On calm, clear nights the rule flips near the ground: cold, heavy air drains downhill and pools in valleys, so the slopes above can be warmer than the valley floor. That's called a temperature inversion.
Questions people ask
- Why is there snow on mountains in summer?
- Temperatures near high summits stay cold enough for snow to last, and some peaks are high enough to stay below freezing much of the year.
- Why does water boil at a lower temperature up high?
- Lower air pressure lets water boil sooner: at about 10,000 feet it boils near 194°F instead of 212°F.