28 degrees and raining

General Discussions: ASK John: 28 degrees and raining

By Uncle Ed on Sunday, December 09, 2007 - 05:39 pm: Edit Post

This afternoon I was driving home from a morning hunt and my outside temp guage read 28 degrees, yet it was raining. A week ago it was 34 degrees out and snowing. What exactly causes this varience from the 32 degree freezing point?


By Scott Davis on Sunday, December 09, 2007 - 07:29 pm: Edit Post

Uncle Ed you are experiencing the result of warm air over colder air and visaversa. We really have to watch such things when flying small airplanes without icing countermeasures. We need to know if our safety is higher or lower than our present altitude if we see ice forming on the leading edges of the wings. This information is why we take time to contact FAA weather before every flight.

-Scott


By FRNash/PHX, AZ on Sunday, December 09, 2007 - 10:25 pm: Edit Post

What Scott Davis said. You have to consider the temperatures and other conditions not just where you are, but in a vertical cross section through the atmosphere.

John answered a similar question just last month, see this thread: General Discussions: ASK John: Temp and its relationship to snow


By John Dee on Monday, December 10, 2007 - 01:46 pm: Edit Post

Thanks Scott and FRNash-

Uncle Ed.

Contrary to many persons belief, the conditions at the surface are the least important in determining what type of precip falls. It is the air temperature where the precip forms that is most important and then secondly the air temp between where the precip forms and the surface.

In the case of rain and 28, there was a shallow layer of cold air right near the surface, while temps aloft were above freezing. That caused the precip to either form as rain, or melt to a rain drop. The layer of air near the surface was not cold enough to cause the liquid rain drop to refreeze into an ice pellet (sleet).

In the case of the snowflake at 34 degrees, it was just the opposite. It was cold enough aloft for the precip to form and fall as snow, with the layer of warm air near the surface shallow enough as to not cause the flake to melt.

-John


By DooDad on Monday, December 10, 2007 - 08:38 pm: Edit Post

I Thought This Topic Was Titled... "ASK JOHN"


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