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I have noticed in many movies, including Gladiator and Kingdom of Heaven, that when snow is shown it often appears to behave differently to snow in real life going sideways or upwards.

This can be seen in the clip below from Kingdom of Heaven in the first battle scene, here:

I always find it jarring and pulls you out of the story somewhat.

Why does snow in movies have this behaviour?

Is it because it is fake snow which is lighter than normal snow? Is it to do with the angle it's inserted into the scene from? Or is it some other reason?

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    I have seen even heavy snow "go up" in an updraft. It is not just a feature movies.
    – Yorik
    Mar 22, 2017 at 16:37
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    @Yorik I guess we don't get much snow here to see it do that, or it's wetter and heavier, or I just haven't seen it. Some of the films though look calm wind wise and they still go upwards. No matter have plenty of answers now
    – Cearon O'Flynn
    Mar 22, 2017 at 18:29
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    I was just skiing in Vermont during the latest storm, with heavy winds whipping across the mountainside. Snow can definitely go up, sideways, and any which way if there's enough wind to move it.
    – PoloHoleSet
    Mar 22, 2017 at 21:20
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    Updraft doesn't necessarily mean wind in the same way you might be used to. A small difference in temperature in ground level and higher up is quite enough to cause snow to move up. This is easily seen above tarmac in cities - the tarmac gets heated easily in sunlight, so the air near ground level is significantly warmer and rises, taking the snow with it. In reality, snow can easily move sideways, downwards and upwards at the same time. However, I'm not sure how it would move in a forest (as in the scenes above) - it's been a long time since I've been in a forest while it's snowing :)
    – Luaan
    Mar 23, 2017 at 9:07
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    I live in Vermont, and the snow especially light snow regularly goes upwards. Especially in forested areas or areas near a slope. Basically in any areas of major turbulence. I find the small amount of snow more jarring than the motion of it. Makes me suspect it is an added effect.
    – J Sargent
    Mar 24, 2017 at 18:02

6 Answers 6

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'Movie snow' is made of several different things, each having a different weight & different purpose.

If they'd really wanted it to fall straight downwards, they'd have used something heavier.

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

After comments - I feel it doesn't change the premise of the question whether it's light snow or actually ash in the first-mentioned Gladiator clip. There are plenty of occasions when show flurries in all directions, unless the weather is completely calm and still.
Different artificial snow weights and/or large fans out of shot can change the appearance on-screen to be whatever the director requires.

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    Why doesn't it matter if it's ash? Ash always goes up.
    – Todd Wilcox
    Mar 23, 2017 at 5:09
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    Ash only goes up when it's hot, which it is for a mere few seconds. After that it's just a light particle, following whatever air current there is. Its tendency is actually to fall, once cool.
    – Tetsujin
    Mar 23, 2017 at 7:26
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    @ToddWilcox It's not as if ash went up on its own. It's just that the production of ash is usually associated with a heat gradient, causing updraft that brings the ash up (along with all the other products of the burning, e.g. carbon dioxide). But the movement comes from the bulk movement of the hot air, not from the ash itself. If you just spread ash in the wind, it will move with the wind - it still has a much higher density than the surrounding air.
    – Luaan
    Mar 23, 2017 at 9:11
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    I meant there's always a part of the life cycle of ash where it's going up. And often that part lasts long enough that you don't see it come down because it is so far away.
    – Todd Wilcox
    Mar 23, 2017 at 11:34
  • FWIW I've heard some films have used mashed potato flakes to replicate certain types of snow.
    – Darren Ringer
    Mar 23, 2017 at 17:34
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The premise of the question is false for a couple reasons:

  1. That's not snow in the Gladiator clip, it's ash from the acres upon acres of forest that has been set on fire to kick off the battle.

  2. As other answers have pointed out, snow (or ash, or other things that are light enough) can in real life blow sideways, upwards, or any other direction depending on the terrain, wind, and other factors like the air currents induced by the tremendous heat of a forest on fire. So snow sometimes appears to go up in movies because snow sometimes goes up in real life.

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    The premise of the question is that snow appears to go up in movies, and does not rely on the Gladiator clip at all. Whether or not one of the arbitrarily chosen examples show it or was a poor choice is not relevant. That the Gladiator clip may have been ash is irrelevant, as it was only an illustrative example. Just ignore it and look at the second clip, or remove the examples entirely, and nothing changes. Also your point 2 doesn't add anything to the answer set here.
    – Jason C
    Mar 24, 2017 at 16:33
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    @JasonC At the time I answered, the only clip in the question was from Gladiator.
    – Dan C
    Mar 24, 2017 at 18:23
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    The context of your answer makes more sense given that.
    – Jason C
    Mar 24, 2017 at 18:29
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I've seen light snow, such as may be depicted here, be blown around up, down and sideways in a light breeze so it doesn't look unusual at all to me.

Snowflakes are very light...so it wouldn't be unusual for them to be caught by the wind.

As for the specific scene, in fact, what we might be seeing is ash and not snow (although snow is more likely) ....either way both are light enough to be caught by the wind.

There's no reference to snow in the screenplay so it's possible it was actual snow that started falling while they were filming.

enter image description here

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    For what it's worth, my recollection is that they filmed that scene in the woods near to where I grew up (a quick google confirms this). I remember walking around the set while they weren't filming, and being fascinated by -- as I remember it -- the patches of fake snow on the ground. Not residue from fake falling snow, but intentionally placed patches to make it look more wintery. As I remember it, there wasn't any real snow fall at that time of year, so I don't imagine actual snow would have fallen during filming. This was, of course, 20 years ago, so should be taken with a pinch of salt.
    – owjburnham
    Mar 23, 2017 at 11:45
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It's quite possible this was a deliberate effect to give the viewer the feeling that there are a lot of fast moving, deadly things moving around (creating a whirlwind). Sometimes it's normal. At other times, it appears to be for dramatic effect to offset an otherwise boring scene.

At time 3:25, we see an outright melee. The snow is going every which way to show that things and people are moving around quickly.

At time 3:35, we see a quieter part of the battle (only one horse running in the background while a soldier falls). The snow is "normal".

At time 4:53, we see the emperor being dramatic with expression, but nothing else is going on. The snow moves sideways, but you also clearly see two flags in the background being blown about by the wind. The snow moves sideways because of the wind -- and too add dramatic effect to the character, showing the conflict he feels in his soul. What's not natural here is that his hood is not being ruffled by the wind to match the snow and flags.

Of note: Sometimes we do really perceive some things appearing to move backwards with the Wagon Wheel effect. (Doesn't apply here.)

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Just a few weeks ago snow (not ash) was doing this outside my window. There was no breeze to speak of. That did not matter. The air around us is nearly constantly in turmoil on many spatial scales. From moment to moment laminar flow and turbulent flow may switch their dominance, typical eddy size distribution may vary, and velocity may vary, but the motion and turbulence affects all spatial scales to one degree or another. Look at how dust in a bedroom sunbeam is moving around, without aid of outside air current. So, yes, that could happen. If you have ultralight particles, they will move pretty much 100.0% in any random direction, without a dominant downward direction being perceptible.

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There is one very simple explanation for the effect - it is the same thing that causes tires to appear to be rotating backward in car commercials. It comes down to the sampling rate of the image. All movies are created by taking a sequence of frames that are then assembled together to form a movie.

Imagine shooting a turning wheel. After each frame (at say 60 frames per second), the wheel turns by some amount. If the amount the wheel turns causes the next spoke to be slightly behind where the first shot spoke was, the wheel will appear to be rotating backward.

Since snow (or ash or rain) may fall nearly uniformly, the same effect can be observed when creating a movie, that is, the particle from one frame has moved downward just enough to appear ABOVE a similar particle in the previous frame. If that happens enough, the particles will APPEAR to be moving upward.

Another example illustrating the same concept is chasing lights on a marquee (sign). The lights appear to be spinning around, but in fact, all that is really happening is that adjacent lights are turning on and off giving the appearance of motion.

Finally, the reader can conduct their own experiment with a fan illuminated by a stroboscope. Adjust the speed of the strobe (or fan) until the fan appears to either spin forward, backward or to stand still. The motion of the fan never changed, only the way the images were captured.

NOTE: The particular scene in the question appears to be exactly what others have said... snow drifting upward and sideways due to air currents.

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