Tonight, look for mostly clear skies and lows around 20. Tomorrow is still shaping up to be largely sunny, but noticeably colder. Sioux Falls will the one of the warmest spots, but daytime highs will likely be earlier than normal, before slight cooling before sunset.
There is a snow chance to talk about late tomorrow and into Tuesday morning. The best chance is in the northwest Black Hills, as the wave comes out of Wyoming. Most snow totals will be on the light side, especially if any falls southeast of the Badlands.
There is a very slight chance of light mix in the extreme northeast reaches of KELOLAND Monday night.
After that we're looking for seasonal temperatures, with highs around 30 for most of the workweek. Wednesday morning looks like the coldest of the period, with many single digit spots.
An Arctic push of colder air starts tomorrow. Winds are out of the west right now, a signal of a quick shift. Most of the front will be dry and we'll only have a brief cloudy period with its arrival.