Keeping your car in a garage or parked outside has weather related risks. The major ones are summarised below:

Warm Front: 

My DB7 had a water puddle underneath on the garage floor, this small puddle was caused by warm front condensation.  This incident and the damaged cause  was the inspiration for producing this weather warnings service. 

A properly prepared car stored at constant temperature near or below zero will suffer no ill effects.  The problem is that warm air holds far more moisture than cold air.   When this warm humid air comes  into contact with your still cold car,  moisture will condense out.   This is exactly the same process as a mirror in a bathroom.  This condensation can be really bad if a strong warm front follows a sustained period of low temperatures.  The condensation will not only be on the exterior of the car,  the engine bay and suspension will also attract moisture.  The main saving grace is that condensation is pure water and does not have salts.  It will dissolve any dried out salts on the surface and start to cause corrosion.  Condensation will not only effect the car,  tools and metal equipment will can also get wetted and start to rust.   

The image above in warm front condensation on a metal cooling water header tank.  This is under the bonnet of my car.  Water has even condensed on the rubber overflow pipe.  This is why you should sign up for weather warnings.  

Powerful warm fronts following a long cold spell are relatively rare in the UK, but they do occur every year.  It takes a car in garage a long time to cool down or heat up,  so it will sit at around the average of the Day/Night temperatures.      AstonOwners.com weather warnings server models the temperature of the your car from the forecasts in your area.   It also spots when your local weather  forecast predicts the approach of a warm front.  It will then warn you that condensation could occur.   These warm front effects can be minimised by:

• Stopping the damp warm air flowing across the car
• Air conditioning or dehumidifying the garage. 
• Preheating the car slightly.  

A sealed chamber kept inflated by a fan is probably the worse thing with a warm front.  It is best to turn the fan off when a warm front comes along.   Heating, dehumidifying  or air conditioning a garage constantly is very expensive and environmentally unacceptable,  whereas heating or dehumidifying a garage to stop the worst effects of a rare event is OK.  When a warm front warning for your area is sent to you, turn on a small heater or de-humidifier a few hours before.  This will 

Frost or freezing:

Sustained low temperatures will not normally damaged your car in an unheated garage, but some simple precautions must be taken.  A fully charged battery can withstand -70 C.  At 50% discharge this falls to -25 C.  If your car is fully discharged this falls to  zero C.  The battery will freeze and the resulting expansion will probably crack the battery and when the frozen water melts, the weak acid will leak into the car.   

Storms:

These can cause horrible and heart wrenching damage to your beloved car, especially if hail in involved.   Aluminium is easily deformed, and it requires a specialist to repair the damage these numerous small dents.   Whilst the darkening skies of the approach of the thunderstorm can be seen.  The severity of the hail within the clouds is much harder to predict.  

In the UK in the early evening of 21 July 2021, hailstones the size of golf balls pelted suddenly from the sky, smashing windows and battering cars. Gardens that were a few moments earlier filled with people soaking up the evening sun, were left badly damaged by the downpour of ice.

While the hailstorm – caused by strong updrafts of cloud high in the atmosphere – was unusual in its severity, it was mild compared to a hailstorm that struck Calgary in Canada in June 2020. Hailstones the size of tennis balls caused damage to at least 70,000 homes and vehicles, destroyed crops and left the area facing a C$1.2bn (US$940m/£720m) repair bill. The 20-minute hailstorm was one of the country's most costly weather events.

Protection from the more usual heavy hail storms is easy.  Park it under a roof of some type.

UV damage: 

Leather and even some paints react very badly to high UV levels.  The more exclusive and rarer leather colours usually fade the most. (ask any Aston Martin owner with an aniline leather interior).  It's very simple to prevent by parking in the shade or covering the leather with material.  

For drivers of open topped cars, this can mean that roof should be up, but for or some Aston Martin owners this is not an option (see pic below). The only option is  a lot of sun-screen and a big hat.....

High winds: 

The example below is extreme, but branches fall more often than many people realise.  The tree below was obviously rotten, but who is liable?  It can be an insurance requirement to have tall trees inspected by an expert every 5 years.  So expect a lot of arguments over liability.

A loosely flapping outdoor car cover will wear through layers of paint over a long period of rubbing.   So make sure that you car cover is well secured.