Ask Josh: Wintry Precipitation

Meteorologist Josh Fitzpatrick explains how different forms of wintry precipitation develop.

We've had several rounds of wintry precipitation the last couple of months.  It's not been much but a little goes a long way when you're dealing with snow, sleet and or freezing rain.

I got an e-mail recently from a viewer who asks: "How can it rain when the temperature is 30 degrees?  Why wasn't it snow?"

That's a very good question!  It's a little complicated but it all has to do with the temperature profile of the lower atmosphere.  I've included a graphic to illustrate this temperature profile and the different precipitation it brings.

Precipitation Chart

Nearly all precipitation, especially in winter starts out as snow in the clouds.  But if there's a very thick layer of warm air, above 32 degrees the snow will melt into all rain. 

If there's a shallow layer of cold air, below 32 degrees at the surface and rain drops fall through this thin layer of cold air the rain will become what is known as super cooled.  Meaning the rain drops cool to 32 degrees or below but don't freeze.  They freeze upon impact with a surface that's at or below freezing and forms a glaze of ice.  This is called freezing rain and it's the most dangerous and damaging of all winter precipitation.

Below is a picture I took of the massive ice storm which hit during the Presidents Day Weekend of 2003 in Gallia County, most of Southern Ohio and Northern Kentucky lost power for several days due to more than 25 hours of freezing rain!

Sleet is different from freezing rain.  Sleet is basically frozen rain drops.  When rain falls into a thicker layer of subfreezing air the drops freeze forming sleet.

You get snow when the temperature is at or below freezing from the cloud to the surface.  Although it can snow at temperatures higher than 32 degrees at ground level.  But only if it's a shallow layer of above freezing temperatures as the snow flakes won't have time to melt into rain before reaching the ground.  Of course in order for snow to stick and accumulate the surface temperature must be at or below freezing.

I don't know about you but I'd much rather have snow than a cold rain!

Keep those great questions coming and if you have a weather related question or comment just simply post it below in the comment section.  Thanks for reading!  :-)

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