High temperatures across the area on Saturday were amongst some of the coldest in the nation, even compared to interior Alaska. High temperatures on Saturday at both Chicago and Rockford were 65 degrees. This broke the previous records of 69 at Chicago and 67 at Rockford for the coldest afternoon high temperatures for the 27th of July on record. As you can see from the temperature image, this "cold bubble" is very regional, really only confined to the Upper Midwest and Great Lakes region. Elsewhere, temperatures are much warmer. Notice that even much of interior Alaska topped out in the lower 80s Saturday afternoon, which is a good 15+ degrees warmer than the 65 degrees recorded at both Chicago and Rockford. In addition, temperatures in Europe and Asia are also very warm, with day time highs there reaching well into the 80s and even the 90s in many areas.
The main reason for this cold is the presence of an unseasonably strong upper level area of low pressure centered over the western Great Lakes. This strong upper low has resulted from a buckling of the upper level jet stream, which in turn has allowed a much cooler, more autumn-like air mass to spill in across the region. Typically when the upper level jet stream buckles in this fashion, areas several hundred miles upstream (to the west) and downstream (to the east) experience much warmer conditions. This is what is happening in this case, as areas in the high latitudes of Canada and interior Alaska are very warm. This is a weather pattern more typical of the cool season, such as the spring and fall seasons. It is somewhat rare to experience such a weather pattern in July.