Orsdxy

Usually it takes more than a year to film a good movie. Some movies take place in only one season. For example, Home Alone takes place in winter.

How do they manage to film a two-hour movie in three or even less months? They can not change the location of filming, it's impossible to create the season artificially, then how do they do it?

Principal photography, where the actors are in front of the camera, usually takes less than 3 months. I've heard of movies being shot in just 21 days. But the whole production of a movie involves a lot more than just principal photography, and can frequently take a year or more. Movie production is generally broken into 3 stages:

1. Pre-production: The script is finalized, crew and cast are hired, rehearsals, location scouting, costumes, props, permits, etc. This usually takes several months.




2. Principal photography: The actors are on sets or on locations, being filmed. This takes 1-3 months, typically.




3. Post-production: Edit the film, score the film, add special effects, ADR (recording the audio of voice-overs and the like), marketing, etc. This is often the longest part of a film's production schedule, often taking 6 months or more.

So principal photography can easily be completed within one season. In addition, as others have pointed out, much of what you see is "movie magic": fake snow on the ground, the actors pretending to be cold when it's actually summertime, etc. Also, the environment only needs to look like a particular season for shots taken outdoors; if the actors are indoors, they can shoot that at any time of the year that they want.

To take a single aspect of this, 'winter'...

Fake snow is big business.

In the UK, the snow companies are busiest in summer, when it's [theoretically] least likely to rain and spoil the effect.

From my own answer on Why does snow appear to go up in movies?

I've seen sets dressed for snow and worked on scenes using it, but I
don't know the full technical details, so I'm going to have to skirt
the 'hard data' a bit.

The basic types I've seen are made of paper [wet or dry], foam,
cellulose and formaldehyde.

The very light 'snow' is formaldehyde, burned as candles - that will
definitely give the look in the Gladiator clip.

Foam, as far as I know, is used for heavier snowfall.

Paper and cellulose are also used to make snow-fall, but I've never seen
those in real life, only on other people's footage. I've seen it laid
down on the ground as a blanket effect prior to the shoot, but not
used as fall. Paper is extremely good for ground-coverage. If you wet
it slightly it even holds footprints that look and feel entirely
convincing even when they're your own feet making them and it's 30°C in
the shade.

Have a look at Snow Business, a UK company, for the myriad ways
they have of trying to convince you it's actually snowing.

...and I only just realised, that's the company who did the snow for
Gladiator! See the page on Snow Sticks

Here's a rare picture of a set in the middle of being dressed for snow for the xmas episode - this was taken in mid-July, the temperature was about 30°C.
The 'snow' on the ground is predominantly paper or cellulose, slightly damp - as you can see in the foreground it is holding footprints well. By the time they'd finished, it was deeper than this and covered most of the set; walking across it would leave prints but not show the ground underneath.

I found this - I didn't work on the show the year they did "The Big Freeze" my shot is from a couple of years earlier - but they made a special on 'the making of', posted to YouTube...

Less important, but principal photography is unlikely to span a year - more like 2 months, whatever the weather.