No Prediction, Just a Lot of Scenarios

question-mark-dice The word of this year’s Christmas holiday is… Patience.  Eastern Iowans will need a lot of it as a storm system barrels through and gives forecasters a holiday headache.  There’s no easy way to pin down exactly what’s going to happen. For now it’s time to hope for the best, plan for the worst and wait and see.

Even with the bulk of the storm system knocking on our door, the models can’t nail down what will happen.  This is an especially difficult storm to forecast for because of two key reasons.  1.) Four different types of precip are possible.  A degree or two shift in any direction in a couple layers of the atmosphere could make a significant difference.  And 2.) A number of factors affecting surface temperatures will also play a crucial role in the final product of that precipitation.

So let me break it down for you.  Beginning today, a large duration precipitation event will blanket eastern Iowa and the rest of the Upper Midwest.  As for what will fall where, it’s anyone’s guess.   The National Weather Service, and myself, remain concerned over the potential for ice accumulation along and north of Highway 30.  This includes the Cedar Rapids, Waterloo and Dubuque areas.

RUC_255_2009122311_F09_42.0000N_91.5000W Temperatures at the surface Wednesday morning are ripe for freezing rain.  But with so much warm air surging up from the south, the rainfall could bring with it enough warm air aloft to warm the surface.  If that happens, no major problems, just a lot of rain and potential ponding in areas where the water has nowhere to go.

BUT, and that’s a big but, Strong winds out of the east could limit the warm air’s ability to increase temperatures at the surface.  If that were to happen, by just one or two degrees, portions of eastern Iowa could face a major ice storm both Wednesday and Thursday.  At this time it’s believed ice accumulation is possible in eastern Iowa Wednesday afternoon and early evening.  Later tonight temperatures should increase and should warm the ground enough to prevent any ice accumulation.

That doesn’t mean we’re out of the woods yet, ice is still possible further north along and above Highway 20.  An ice storm remains possible there as well.  Beyond ALL this, we still face a threat of measurable if not significant snowfall over the Christmas holiday.  With a changing track of the storm center and a potential stall over eastern Iowa, heavy snow remains a threat over much of the area.  This will  have to be monitored, but for now all eyes are on the rain and it’s potential to freeze on the ground and on vulnerable objects like trees and power lines.

This in an EXTREMELY fluid and constantly changing situation across the state.  It’s safe to say we’ll not be able to continue long discussions like this and will instead focus on smaller, more frequent updates.  Please stay safe, stay informed, and stay out of the elements if at all possible in case conditions deteriorate rapidly.

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