Our next storm is here and it's anxious to get started with drizzle falling across much of the metro. But the majority of the precipitation will hold off until this afternoon and evening as a deepening area of low pressure scoots through. This will eventually lead to cooler temperatures and the change over from rain to snow.
So why are temperatures so warm to start?
Well, it actually has to do with the amount of moisture. When looking at a surface map, like the one below, you can see green numbers and red numbers. The red numbers are the current temperatures and the green numbers are the current dewpoints.
This image was taken around 6am and it shows an area of southerly winds and above freezing temperatures. But temperatures aren't above freezing simply because warm air moved in, which is what happens a lot of times during the day, but they are warmer because more moisture moved in. Notice the actual dewpoint numbers are above freezing, and in many cases, about the same as the current temperatures.
One rule of meteorology is that your dewpoint can NEVER rise above your temperature because the dewpoint is a measurement of how much water is in your air. So if you add more moisture to the atmosphere and your dewpoint jumps from 20 to 38 degrees, then your temperature cant under any circumstances be below 38 degrees. That's exactly what happened overnight.
Unfortunately for those that are sick of winter, cooler air will dive back in later on today and bring with it several inches of snow in some cases. Here is a look at the current projected liquid precipitation totals from across the area through Friday morning.
A solid half inch of liquid is expected to fall. Now in most cases, that will be a combo of rain and snow. So how much snow is coming? According to a few computer forecasting models, it could be several inches…
They appear to be pretty consistent with their placement that parts of eastern SD and central MN will get a thin band of 3 to 8 inches of the white stuff with more of a slushy inch or two for metro locations.
Remember though that these models don't take melting into account. With temperatures so close to freezing, some of the snow will actually melt on contact slowing the overall accumulation process leading to lower accumulation totals. But regardless, a 3 to 6 inch band looks pretty likely.
If you are looking for more of a probability forecast… here is what the Weather Prediction Center is showing for at least an inch, 2 inches, and 4 inches.
According to the WPC, most of us will see at least an inch of snow, with the heaviest band setting up from about St. Cloud through the Duluth area with at least a 70% chance of 4 inches.