Here is the general temperature profile of the atmosphere when you get the four main types of precipitation. Freezing rain is the one that coats everything in ice and can make it impossible to travel... even more so than snow.
(KMSP) - While many of us are focused on the “impending doom” of more April snow, I think we’re really missing the headline here; the potential for some significant freezing rain.
The small nuances of a winter-style storm in April prevents us from forecasting anything with any certainty, but all of the components appear to be ripe for several hours of freezing rain Friday night… topped off with the snow after that of course. This would likely have a MUCH larger impact on the metro than snow alone in April ever would.
Freezing rain occurs when snow hits a warm layer of air between its origin, the clouds, and when it reaches the ground. This warm layer has to be warm enough and/or large enough to completely melt that snowflake back to water. So the snowflakes melts into a raindrop and then gets to the ground where temperatures are again below freezing. When the drop of water then hits anything on the ground, especially power lines, tree branches, rooftops, and bridges, it freezes. So it’s rain that freezes when it hits the ground, hence the term freezing rain.
This then brings up another question, why doesn’t the raindrop switch back over to a snowflake when the temperatures gets below freezing as it nears the ground? Well, snow production in the atmosphere is exceedingly complex and needs the perfect conditions to form… and snowflakes CANNOT form from raindrops… so once a raindrop forms in our atmosphere, it either hits the ground or evaporates before hitting the ground. It will NOT turn into snow.
The reason for the potential large-scale impacts of freezing rain is that it forms ice, which is nearly impossible to walk on, let alone drive on. Not to mention, if you get enough of it, generally over quarter inch, tree branches and power lines start to come down and power can be out for days… or even weeks in the worst of circumstances.
Snow, especially in April, is heavy, wet, and slushy, and has a hard time from melting altogether. While heavy snow can bring down trees and power lines, you usually need leaves on the trees for it to have a significant impact on our daily lives, and clearly leaves aren’t budding anytime soon. The high sun angle also helps to melt the snow before it accumulates. It can snow, fairly heavily in some cases, during the daylight hours in April, and overall snow accumulation may be next to nothing because the incoming solar radiation, even through the cloud cover, is high enough to warm the ground to the point where snow can’t stick.
Ultimately, if you need to do some traveling this weekend, or you just want your power to stay on… I would pray for snow and hope the freezing rain stays away.