The contoured version provided is not the only correct interpretation of the data. Though your contour analysis may look different, it may be correct, as there are many possible variations. Starting with the surface maps and then working up in height. The main feature is the low pressure system centered over Minnesota. The low pressure system represents converging surface air.
Laws of physics require that air flow from from higher pressures toward lower ones.
The air is then moving toward the low pressure center due to the strong pressure gradient . One would think that the air would cross the isobars perpendicular. This doesn't happen as the coriolis effect turns the air to the right in the northern hemisphere, thus the flow of air is parallel to the isobars in a counter-clockwise rotation. However, friction at the Earth's surface then turns this air to the left by about 20 . The net result is air converging at the low pressure center.