The image above shows projected vorticity values on May 5th. Vorticity is the spinning of air, and appears in the presence of storm systems. We see high vorticity values centered in the Midwest, curling into a circular formation across the north-central states. This circular motion in the vorticity areas, combined with multiple full-circle contour lines across the Midwest and the general north-central United States region indicates we are dealing with a massive closed low. The closed low is formed when a storm system is cut off from the jet stream and meanders along with little to no influence from the jet stream. Usually, closed lows are relatively small and are more of a nuisance event. This closed low, however, will be of pattern-changing status. This closed low is just like the others, except it will be so large that the weather pattern across North America will be altered as a result.
What can we expect from this event?
The answer is just what you hope it isn't: we are expecting snowfall across portions of the Midwest, Plains and Ohio Valley. At the moment, accumulation appears possible in areas of higher elevation and areas in the western Ohio Valley. The closed low will bring down a massive bubble of cold air from Canada and spread it around the central and east US to provoke multiple chances of (possibly accumulating) snowfall.