A winter weather advisory is in effect for the areas shown in the graphic below in central and western Iowa until Noon on Saturday. An ice storm warning will go into effect in the counties highlighted in the darker color in the second image tonight, where more ice is expected to accumulate by Saturday morning.

Precipitation type depends upon how much cold air we have aloft and at the surface, as shown in the diagram below. Precipitation that falls through above freezing air from the top down does so as rain. If the layer of subfreezing air at the surface is around 1000′ or less thick, rain will freeze on contact with the surface, as will be the case tonight. Thicker subfreezing air causes raindrops to freeze into sleet pellets, and cold air all the way up through the cloud layer gives us snow. We’ll see all of these in central Iowa over the next 24 hours.

The weather timeline shows us temperatures rising slowly during the overnight hours into the morning, changing our precipitation from freezing to rain.

As shown in the gallery below, freezing rain will gradually spread northeast during the evening and overnight. In the Des Moines area, this should begin after 8pm and last until roughly 8 in the morning before changing over to rain. It’s possible we’ll see snowflakes mix in at times. Rain looks to end Saturday evening.

Lows tonight will be set early as temperatures begin to rise.

A look at expected ice accumulations. These will be heavier in general east of Highway 14 in Iowa. If the system continues to slow down, we may see another 0.1″ or so of accumulation in central Iowa. In the Des Moines metro area, best to prepare for 0.1″ – 0.25″.

We have very slim precipitation chances beyond Saturday evening, with light rain being possible early Monday morning.

Highs for the next 6 days can be found in the gallery below:

Looking ahead, the chances for a white Christmas seem low in central Iowa temperatures look to stay warmer than average in the outlook below.

Your WHO 13 7-day forecast: