Freezing Rain

[Pburgh]

I'm in Pittsburgh, Pa. This morning I woke up to ICE everywhere. My trees, evergreens, lawn, house, sidewalks and driveway were totally covered with almost 1" of ice. The temps were in the 20's.

My question is: with the temp so low, why wasn't this snow? Why did we have freezing rain?

[JonathanBelles]

I'm in Pittsburgh, Pa. This morning I woke up to ICE everywhere. My trees, evergreens, lawn, house, sidewalks and driveway were totally covered with almost 1" of ice. The temps were in the 20's.

My question is: with the temp so low, why wasn't this snow? Why did we have freezing rain?

The cool layer was too thin. The moisture didnt have enough time to freeze in the air, so it froze on contact in that very small cold layer. Temps may have been in the 20's at the ground, but they may have been 35+ a few hundred feet up.

[Ed Mahmoud]

Just checking around Schenectady and Wooostah, Mass. About six tenths of freezing rain already, pretty close to what it takes to start knocking out electricity.




When I lived on Long Island, I remember only a single ice storm. Snow would go to rain at a temp a few degrees above freezing. Hard to trap a shallow layer of cold air on a fairly flat island surrounded by water on three sides.


Now, freezing rain is about as common in Dallas as snow. And wet bulbing plays a part as well, when it does ice down here.

[wall_cloud]

could be two factors.

1) snow needs ice crystals to develop. These ice crystals are generally found at temps colder than -10C (which is usually in the mid levels. As this snow forms, it falls through a warm layer (inversion) and melts. The air is cold at the surface (indicative of a shallow cold airmass), causing the rain to freeze on contact. If this freezing layer is sufficiently thick, it will become sleet. Now snow CAN develop in the low levels (generally a very cold airmass) but this is usually light. once these ice cyrstals/snow melt in the warm layer, they usually don't change back.

2) If the air is dry aloft, there may be no ice crystals. Therefore...snow has a difficult time forming. Any isentropic ascent (overrunning) or large scale lift from an upper level system could squeeze out some light precip from the moisture found in the low levels of the atmosphere. This precip usually falls as freezing drizzle/rain...but can mix with some sleet or very light snow.

A) is a freezing rain sounding, B) is a snow sounding...

A


B

[wyq614]

Freezing rain often occur in China's Guizhou and Hunan Provinces in winter.