Mike - both are normal. The steam you see, as people explained above, is rain water evaporating after coming in contact with the hot radiator. The reservoir works in tandem with the radiator, when the pressure in the radiator gets higher (as in when the coolant gets very hot) some coolant is displaced into the reservoir as the pressure inside the radiator increases. When the coolant temperature and pressure goes down, some of the coolant is sucked back into the radiator. There always is an equilibrium point to this system, it varies with temperature and system pressure.
Assuming there is no leak in the system, as the outside temps decrease in winter, the "cold" temperature and pressure are lower than those of summer, therefore, there could be less coolant in the reservoir than you saw during hot summer days after the bike has cooled down. The radiator cap controls this flow. If you are getting abnormal flows (in either direction) it's possible that the cap is not working properly. Remove it and verify that it's clean, that there is no grit that could be causing malfunction of the pressure or vacuum valves.
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