You didnt say what year your Volvo is, nor the type of motor or the miles on the car. I will presume it is gas, not diesel. The only difference between parking it outside over night versus inside, is a minor difference in the low temperature it will see, and the degree of humidity. So the way its starting now when parked outside, will soon be the way it starts when parked inside too.
How long since the spark plugs, plug wires, distributor cap and rotor were renewed? When those things get old enough they get sensitive to moisture under the hood. This is likely to be worse if the car is parked near salt water.
If the ignition system isnt the problem, try unscrewing the fuel cap the evening before and leaving it loose overnight. It the venting system for the fuel tank is clogged up it can affect the fuel pressure seen at the injectors. Outside of California I doubt more than 1/4th of the evaporative canisters on older cars are still working at all. I dont know about this in California.
You might want to try spraying throttle-body-cleaner onto the inlet for the Idle Air Control valve. They eventually get sticky from dirt/moisture and can misbehave.
Another thing to look at: I think if that large rubber tubing that feeds into the throttle body gets a hole in it - even a small one - it will quickly mess up the air/fuel mixture.