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Falling Snow Animation (Plugin-Free Particle Expression)

About This Expression

This expression creates a smooth, looping falling snow animation without using any plugins or built-in particle systems. Each layer behaves like an independent snowflake, falling from the top of the composition to the bottom with natural variation.

The animation relies on deterministic randomness, controlled by:

seedRandom(index, true);

This ensures that:

  • Every layer has unique movement
  • The motion stays consistent across previews and renders
  • Duplicating a layer instantly creates a new snowflake with different behavior

The result is a lightweight particle system that feels organic, efficient, and fully customizable.

Vertical Movement
Each snowflake falls downward at a random speed using modulo logic. When it reaches the bottom, it resets to the top seamlessly—without popping or visible jumps.

Horizontal Sway (Wind Effect)
A sine wave is used to create gentle side-to-side motion, simulating wind. Each flake has its own sway frequency and wind strength, which prevents the movement from feeling mechanical.

Advanced Boundary Logic
The expression calculates the object’s actual height using sourceRectAtTime() and adds a safety buffer. This ensures flakes:

  • Fully exit the frame before resetting
  • Never clip or pop on screen
  • Remain visually smooth even when rotated or scaled

Expression

seedRandom(index, true);
speed = random(100, 400);
windAmt = random(-100, 100);
swayFreq = random(0.5, 2);
startOffset = random(0, 10000);
startX = random(0, thisComp.width);
// We measure size at time 0 to prevent jitter if the flake rotates
rect = sourceRectAtTime(0, false);
scaleY = transform.scale[1] / 100;
objHeight = rect.height * scaleY;
// We add a safety buffer so it doesn't pop visibly
safetyBuffer = 100;
// The total distance the flake needs to travel before resetting
travelDistance = thisComp.height + (objHeight * 2) + safetyBuffer;
t = time + startOffset;
// Vertical Movement
startY = -objHeight - safetyBuffer;
y = startY + ((t * speed) % travelDistance);
// Horizontal Sway
x = startX + Math.sin(t * swayFreq) * windAmt;
[x, y];

How We Use This Expression

Step 1: Create a Snowflake Layer

  1. Open your composition in After Effects
  2. Import or create a snowflake shape / PNG / text layer
  3. Place it anywhere in the comp (position doesn’t matter)

This expression works on any layer type that has a Position property.

Step 2: Apply the Expression to Position

  1. Select the snowflake layer
  2. Press P to reveal Position
  3. Hold Alt (Windows) / Option (Mac) and click the Position stopwatch
  4. Paste the full falling snow expression
  5. Click outside the editor to apply

The layer will immediately start falling from top to bottom.

Step 3: Duplicate for More Snow

  1. Select the snowflake layer
  2. Press Ctrl + D / Cmd + D multiple times

Because the expression uses:

seedRandom(index, true);

Every duplicated layer gets:

  • A different falling speed
  • A different wind sway
  • A different starting time and position

Instant particle system—no plugins required.

Step 4: Adjust Snow Behavior

Inside the expression, tweak these values:

  • speed → slow snowfall or heavy storm
  • windAmt → calm drift or strong wind
  • swayFreq → gentle float or chaotic motion
  • safetyBuffer → ensures smooth off-screen looping

All changes update live.

Step 5: Scale & Rotate Safely

  • You can freely scale or rotate the snowflakes
  • The expression measures the layer size at time 0, preventing jitter or popping

This keeps the loop smooth even with animated rotations.

Step 6: Loop Without Pops

This expression uses modulo logic to:

  • Reset snowflakes above the screen
  • Re-enter smoothly from the top
  • Avoid visible popping or clipping

Perfect for infinite loops and long renders.

Step 7: Style the Snowfall

You can enhance the look by:

  • Adding Blur for depth
  • Using Opacity variations
  • Creating multiple snow layers (small, medium, large)
  • Applying Tint or Fill for color themes

The motion logic stays untouched.

Best Use Cases in After Effects

  • Snowfall & winter scenes
  • Holiday promos (Christmas, New Year)
  • Website background loops
  • Cinematic atmosphere shots
  • Confetti, dust, ash, or rain effects

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