FIRST WINTER STORM: Rain for all, snow for some

- It’s the middle of November and it’s finally going to start looking and feeling more like it. Minnesota's first winter storm is moving in, and while everyone will likely get wet, only some will get white. 

RAIN FOR EVERYONE: First things first, this is a fall-type storm so everyone will start their precipitation as rain. The ground and the atmosphere are just too warm for the precipitation to begin as snow.  But as cooler air dives southward and falling precipitation helps to further cool the ground and the atmosphere, the rain will switch over to snow, likely from west to east across many areas. 

LOCATION, LOCATION, LOCATION: Your location will depend on the exact switchover. Areas in western Minnesota can expect the changeover sometime Thursday night. For northern and central Minnesota, it will likely be sometime Friday morning.  For the metro and areas east of 35, it won’t be till Friday afternoon as the storm is moving out.  This will create some pretty big differences in overall snow accumulation with 6”+ for areas of western and northern Minnesota, with maybe a slushy inch or so in much of the metro, and little if any accumulation (or even flakes) for western Wisconsin and the southeast.

SO WHY THE BIG DIFFERENCE? Well, as our low pressure and storm develop, they bring a lot of warm air and moisture along with them as they push in from the southwest. This causes a delay in the overall cooling of the atmosphere and creates different types of precipitation depending on temperature. For it to snow, the ENTIRE column of the atmosphere has to be below freezing. Well, when warm air and moisture are pulled in from the south, the several thousand feet of atmosphere closest to the ground will be above freezing.  It’s not until that “warm bubble” of air moves out that temperatures can cool enough for rain to change over to snow. 

CHECK OUT THE MAPS (ABOVE): Notice the time frame in the progression of pictures above. Starting Thursday evening, the freezing line is in the Dakotas with all areas getting rain. But as we push through Thursday night and into Friday, the freezing line collapses east allowing snow to begin falling across the west and north… finally ending in the metro likely sometime Friday afternoon as the precipitation is winding down.

This is why some areas will get A LOT snow and other areas get a whole lot of nothin!


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