The GFS had gone to crap for this storm largely because it tried to stretch out and yank eastward the northern part of the western energy, which led to postively-tilted, suppressed nothing. The model is now furiously trying to undo that scenario. Now, instead of the energy getting sheared apart and whisked away, it holds it back and even closes it off over Iowa with the 18z run, which obviously leads to a very different result.