The biggest storms in the northern plains tend to come in from a southwesterly direction. Storms making that track have more time to advect moisture from the Gulf of Mexico into the storm and in turn drop more precipitation. The storm on Monday, came from the southwest, but never ventured much farther south than Wyoming, meaning not a huge dip to the southwest to pick up moisture. Our biggest storms tend to dig down to Colorado or even farther south meaning a longer trek and more moisture. Our current flow is more from the northwest meaning even less moisture, but as it the case with generalities, there are exceptions.