What Is Lapse Rate?
Lapse Rate describes how the temperature changes with altitude. Usually, temperatures decrease with altitude, but not always. And while the lapse rate is talked about as a constant, the actual temperature change with altitude can vary quite a bit based on aspects beyond just the physics of the atmosphere, such as the direction the slope is facing, the make-up of the slope (rocks, snow, a lodge) and other factors.
How Can I Use This Knowledge at the Mountain?
When the air is dry, the temperature decreases about 5.5 degrees Fahrenheit for every 1,000 feet gained in elevation. For example, if the temperature at the base of the mountain is 30°F, and the summit is about 2,000 feet higher, you could estimate that the summit temperature would be 19°F (the math: 2,000ft x 5.5°F/1,000ft). In real life, the summit temperature might be a few degrees warmer than this approximation because the ground can stay a bit warmer than the freely-moving air just above the summit.
When the air is moist, like during a storm when snow or rain is falling, the temperature decreases about 3.3 degrees Fahrenheit for every 1,000 feet gained in elevation. For example, if the temperature at the base of the mountain is 30°F, and the summit is about 2,000 feet higher, you could estimate the summit temperature would be about 23°F (the math: 2,000ft x 3.3°F/1,000ft). Just like with the dry atmosphere example above, you could add a degree or two to this estimate because areas near the ground can retain just a bit more heat than the atmosphere just above the mountain.
Why Does Altitude Affect Temperature?
Temperature decreases with increasing altitude because air at higher elevations is at a lower pressure (there is less air above pressing down). When air is at lower pressure, it expands and cools.
To Wrap Up
While these calculations are not a substitute for first trying to find actual measurements from nearby weather stations, they can help when the nearest official temperature measurement is far away.
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