As the storm begins to ramp up, I wanted to take a few moments and show you some interesting things going on with this storm system. This afternoon, an incredibly strong temperature gradient, stationary front, will exist over southern Iowa and southeastern Nebraksa. This is the front the storm will be traversing this evening into the overnight hours. Take a look at how strong the gradient is, the temperature changes from 80°F to 52°F in just a matter of roughly 30 miles. Because of this strong temperature gradient, there will be plenty of moisture and fuel to maintain and strengthen the storm.
One of the greatest challenges with this storm has been pinning down exactly where the northern edge of the snowfall will end up. Typically, there is a sharp cutoff to the edge of the snow band on the northwest side of a strong mid-latitude cyclone. This storm is no exception with a razor-sharp gradient to the snowfall on the northern edge of the storm.
To the right, you’ll see the latest QPF prediction off of the high-resolution NAM model. My point to showing this is that you can see just how sharp the snowfall gradient is. Hennepin county is a great example of this strong gradient. This particular model showing 5 inches of snow in Bloomington, with no snowfall whatsoever in northern suburbs such as Rogers in the northern part of the county.
The biggest reason for the sharp cutoff to the snowfall totals is the dry air being entrained into the storm from the north. The image on the left is the dew point temperatures late this afternoon off of the HRRR model. You can see there is a very defined line where the drier dew point temperatures are advecting into the region. This scours out the moisture necessary to produce snow and creates a very defined northern edge to the snowfall band.
All-in-all, this is still shaping up to be a very sizeable event for the southern half of the region. Widespread snowfall totals of 2-5 inches are likely, with 6-12+ inches south of a line from Worthington to Mankato and Red Wing. In addition, gusty winds to 40mph will create considerable blowing and drifting snow with very difficult travel conditions likely.