Leaving that cracked storm window go until spring is a bad idea. Storm windows create an air gap between the window and the pane. This air gap allows a space for the heat coming in through your windows to disperse a bit, then it is sent back out the window. The glass in your window is actually a heat conductor, as the sun heats up the glass, it allows that heat to pass right through the window. In the winter, the warm air from your heater can pass right out your window. Having this extra layer of glass allows you to have additional protection form the cold and also maintains the air gap between the window and the pane, further insulating your window from the cold.