The best thing to say folks is, “it’s going to be a close one.” A strong storm system is expected to push through the Upper Midwest on Wednesday, bringing with it a rush of warm air and a good amount of moisture for this time of year. The troublesome aspect of this storm system is the timing of that precipitation and its correlation with the warmer air.
In the graphic to the left, the red lines on this forecast model indicate temperatures just above the surface above freezing. The blue lines represent an air mass below freezing. As you can see, with light precipitation in the area, parts of Iowa will be above while others will be below freezing. Even where those red lines cover eastern Iowa, surface temperatures could remain below freezing for a period.
This means with rain falling and a surface below freezing, freezing rain is possible for a short time. At this time we do not believe any significant accumulations of ice or snow are possible because this storm is expected to push in the warmer air rather quickly with the precipitation. As the storm moves out Wednesday night into Thursday morning, parts of Iowa should see a changeover back from rain to snow. Again any snow showers should be light and brief so no major accumulations are expected.
So let’s break this all down, Wednesday morning parts of the state could see freezing rain or some type of wintry mix for a brief period. By the early afternoon hours on Wednesday, Iowans should see a switchover to all rain. This rain will continue most of the day and night until the cold air rushes back in behind a cold front and a brief period of snow could occur before the precipitation wraps up.
With the exception of a flurry or two, Thanksgiving looks dry but downright frigid. A few fortunate people in southern Iowa may see temperatures reach the 30 degree mark on Thursday. Further north, highs won’t get out of the teens and 20’s.
There is a slight warm-up in store for the weekend before another storm system moves in on Monday. Right now the models indicate most of this could fall as snow so it bears watching. For now we’ll keep our sights set on the busy holiday travel time of Wednesday and Thursday. To recap, the period of most concern is Wednesday morning. This is a time where freezing rain could create some icy road conditions. I wouldn’t be surprised with the expected travel to see the National Weather Service issue some type of advisory for portions of Iowa if this verifies.