ASK TOM WHY: What is the highest temperature that will allow snow to form?

Dear Tom,

 

What is the highest temperature that will allow snow to form?

 

— Jerrold J. Smith, Lemont

 

Dear Jerrold,

 

Checking weather records, we found a case in the 1970s when it snowed in Jacksonville, Fla., with a surface temperature of 53 degrees.

 

Temperatures were well below freezing just above the surface and the air was very dry, which allowed cooling from evaporation to prevent the flakes from melting.

 

A snowflake can survive a drop of about 1,000 feet through an above-freezing environment and reach the ground without melting.

 

Longtime Chicago weather observer Frank Wachowski told us he has observed snow here with temperatures as high as the mid-40s, but the flakes melted upon contact with the ground.

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