Answer to "radiosonde" question

RADIOSONDES (SOUNDINGS) -- When it is cold outside and cold enough to snow, how come is it colder up in the sky? Also, if it is so cold in the sky, how come the clouds do not freeze and fall down at once?

Leif lives in Songtan, Korea (Osan AFB) where his dad is stationed." -- 1/28/02

In the atmosphere (at least the part that is within about 10 miles of the surface of Earth - the troposphere), the air temperature usually gets colder as one goes higher into the sky. Meteorologists know this because they send up weather balloons called radiosondes (one is probably sent up from the Air Force Base or at least nearby). These balloons have an instrument package on them that helps tell temperature, humidity and winds. Want to see what a radiosonde sounding looks like? Check one out here! The vertical lines are temperatures, every 10 degrees C.

Above this 10 mile level (and sometimes within it), temperatures can sometimes increase with increasing height. Because this the opposite of what is expected (i. e., the inverse), it is referred to as an inversion. An inversion exists in this sounding from 1435 meters to just above 1900 meters . Another inversion, this one at the tropopause (or top of the troposphere) can be found between around 11,000 and 13,000 meters.

There are many combinations of cloud and ground temperatures and these can lead to different types of precipitation. For discussions here, I will refer only to clouds between the ground and about 10,000 feet (3,000 meters) above the ground; I will also ignore thunderstorms.

Sometimes it can be above freezing at the ground, but below freezing in the clouds. In this case, the snow may melt into rain on the way down or it may still snow, even if air temperature is 40 degrees F.

If the cloud is below freezing and the air from the cloud to the ground is below freezing, then the precipitation will be snow.

If it is warmer than 32 degrees F in the clouds, but below freezing at the ground, then the rain may freeze on the way down (sleet or ice pellets) or it may freeze when it lands on things like cars, or trees (glaze or ice storm).

Clouds don't start to precipitate (rain or snow) until the raindrops or snowflakes inside them get heavy enough to fall; otherwise they float in the wind currents.

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