SO CLOSE YOU CAN SEE IT...
As we all know in the weather game you can be tantalizingly close to a big snowstorm or a sunny warm day but in the end never see a flake or enjoy a ray of sunshine. Forecasting is a tough business and many predictions have busted on a single degree or a distance of a mile. This weekend has a challenge that rears its head when snow is on the ground and warm air sits atop it. It's the dilemma know as the inversion.
Check out what temperatures are projected to look like Sunday morning at 11:00am at 850mb. Here in Cedar Rapids we are shown to be 11 degrees C. which is 52 degrees Fahrenheit. That's at 5,000 feet, less than a mile straight up. So close you can see it clearly on a sunny day.
Unfortunately this time around, we don't live at 5,000 feet and the 50s there will never get down to the surface where several inches of ice encrusted snow cover the ground. In fact, this is what snow cover is forecast to be at noon Sunday. Most of my area still seeing 1 to 7" snow depths.
The snow cover, like a refrigerator keeps temperatures cooled at ground level. As warm moist air over runs the cold dense surface air, it's lifted above the ground where it resides at 5,000 feet. Above that level temperatures eventually cool again. That little warm wedge with cold above and below is the inversion and it can be a temperature buster.
This time of year the sun is not very strong or direct and models are known to over estimate its power and ability to produce sunshine. They see all the warmth above the surface and think that's going to mix down to the ground. Unfortunately, the natural tendency of warm air to rise is a forcing mechanism that produces low clouds and stratus. The weak sun can't burn off the clouds and the potential to warm at the surface is nipped substantially with that cold layer of snow.
What I'm saying is you have to be very careful with temperatures when melting snow adds moisture to an inversion. Instead of a sunny day the clouds hang tough and the resulting low layer of stratus limits solar radiation. It turns out to be a cold dreary day when a model calls for sunshine and much warmer readings. Fog can also be an issue.
This is a simulated satellite for mid-day Sunday. Look at all the sunshine over eastern Iowa and Illinois south of HWY 20. I am very hesitant to buy into that solution and call for much in the way of sunshine (which other forecasts are doing) where there is at least 2 inches of snow.
My belief is that if we don't get sunshine (a strong possibility in many areas) then you know temperatures are going to under perform. Some guidance have highs reaching the mid 40s. I'm having a tough time seeing anything like that getting north of the Missouri border. This high resolution model has readings in the mid to upper 30s which may end up being more realistic for my snow covered counties.
By the way, look at the warmth just to our south where there's no snow and the inversion is not a factor. Spring!
That's all I have to say about that, which brings me to a front that brings the mild weather to a halt Monday and sets up the boundary necessary for snow sometime between Tuesday and Wednesday night of next week. After very good consistency 24 hours ago there's some serious jockeying going on with the models regarding the placement and timing of snow and accumulations. The issue is likely tied to energy dropping into the mean trough digging into the Midwest. Which piece is more amplified and how it phases will make the difference. The EURO is a good 24 hrs. later than the GFS and is stronger and at least a couple inches heavier than the GFS. I usually side with the EURO and am leaning its way but must say there is low confidence at this time...a big change from yesterday. Wouldn't you know! Anyway, here's a look at what the big 2 models are suggesting with their raw snowfall forecasts.
Data should be better sampled in the next 24-48 hours and that will help to verify trends. Meantime, the rest of the weekend is mild for the season and certainly storm free. Have a fantastic Saturday and roll weather...TS