Iowa snow will affect our weather through Thanksgiving

- A band of heavy snow developed Friday and traveled across South Dakota, Nebraska, Iowa, extreme southern Minnesota, southern Wisconsin, and Illinois.  This band dropped as much as 18” of powder on parts of the area. 

While much of Minnesota dodged the major snow storm this time around, the effects will be felt for days to come across the region.  Snow cover doesn’t just provide a beautiful landscape, but it provides freezing power for the atmosphere.  Without snow on the ground, the Earth emits long wave radiation which sends heat back into the atmosphere from the interior part of the Earth.  This, along with warmer ground temperatures, can keep the nights from getting too cold.  But when you block that heat source (however small it may be) by adding several inches of snow or more to everything, it can have a drastic cooling effect on local areas.  With the EXACT same air mass in place, temperatures can vary by some 40° depending on whether your location has snow on the ground or not.  Take Saturday morning for example.  The metro dipped to 16 degrees, but Spencer IA in the northwest corner of the state had a fresh 10 inches of snow.  The overnight low there was -2°.  Same air mass in place, but drastically cooler overnight temperatures all because of the snow.

So how does that affect us in the metro when the snow cover is to our south?  Well, it can prevent warmer air from getting to us.  This upcoming week, southerly winds will grab hold of the Upper Midwest.  While temperatures will warm a bit, they won’t warm nearly as much as they otherwise could have if this storm hadn’t hit areas to our south.  Check out the snow cover as of Saturday morning…

Notice that there is now a couple hundred mile wide band of snow on the ground to our south.  If our winds are coming from that direction, and therefore have to cross over the snow to get to us, the air is actually cooling as it does.  So even if 60 degree temperatures are pushing into southern Iowa, they have to cross over the 20° terrain to get here which means they will be FAR colder than that 60 degrees by the time they arrive.

So for Tuesday, the southerly flow will lead to some 50’s and even low 60’s across Kansas and Missouri, but will hit the snow cover and fall quickly into the 30’s before moderating slightly as it rolls onto warmer ground in MN and the temperatures recover into the 40’s.  Much of the region could have been in the 50s and 60s this upcoming week if the snow hadn't fallen across the I-80 corridor.

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