The last two GFS model runs (12z and 18z) have shown some very interesting weather that could impact much of the eastern half of the country including Iowa about a week before Christmas. Typically this far out we look for any trends that show storm systems that may or may not impact an area with a certain type of precipitation. Take into account what the last two GFS Model runs have shown for the time frame of December 18th-20th.

First we have a graphic that shows the 12z GFS at 6pm Wednesday December 19th (two weeks from tomorrow).

We see with this graphic a very large storm over the western and central Great Lakes with heavy snow and most likely blizzard conditions for portions of Michigan, Wisconsin, Minnesota, Iowa, Illinois and northern Indiana. The black line shows the low pressure center positions according to the 12z GFS at 6pm Tuesday December 18th (the OK/KS border near Ponca City OK) 6am Wednesday morning (west of Peoria IL) and the whole graphic (6pm Wednesday) showing the low centered near Grand Rapids MI. There would be enough cold air for the precipitation to be in the form of snow (GFS shows rain to begin in Iowa quickly switching to all snow). This would bring widespread heavy snow in the black outlined area from KS and NE northeastward to Upper Michigan.

Then came the next GFS Model run at 18z. The storm you see on the 12z run is now quicker but also much farther to the south and brings just a little snow to the state but more cold air than anything. The orange line with black dots shows the low pressure center on the 18z run from Midnight Tuesday December 18th (near Mobile AL) until Noon Wednesday December 19th (north of Ottawa ON in Western Quebec). The snow would be heaviest in the Ohio Valley and through the Appalachian mountains northeastward into New England, leaving most of the Midwest with a inch or two and colder air (which doesn’t last long as the GFS brings warm air back a day later). This is why we say on the IWR, when we show storms and whatnot seven and more days out, things can and are likely to change. We can’t forecast when it will snow if you happen to see something on a model run that screams a blizzard or a big event on a certain day more than a week out. Sometimes you can, if there is a confident enough trend to say so. With this system, we don’t have any confidence at this time.

Will there be a storm around at that time? Chances are yes, trends have shown a storm in the eastern part of the country? Will it impact the state? Too soon to tell. We will know more as time goes by.