GOES-R IFR Probabilities and Surface Observations of ceilings and visibilities, hourly from 1700 through 2100 UTC, 18 April 2013

Chicago O’Hare is a busy hub airport, and obstructions to visibility there have a great impact on air routing.  Thus, any tool that can give information about ceilings and visibilities — IFR conditions — can help.  In this animation from late afternoon on April 18, 2013, IFR Probabilities show a distinct minimum over northeast Illinois, and surface observations from airports in that region are consistent with the lack of low ceilings.  In contrast, higher IFR probabilities exist over Wisconsin, where IFR conditions are widespread.  IFR probabilities are high over Lake Michigan because high dewpoint air is moving over still-cold lake waters;  advection fog results.