©2003 Shane Oborn and CreativeCOW.net. All rights reserved.

NOTE: This tutorial requires the Production Bundle of AE

The look I was going for in "blowing snow" was something similar to the snow that those large machines blow onto the otherwise uncovered slopes of Minnesota during November (and this year, even December!). Obviously, not everyone is going to know what I'm referring to here, but the idea is that these machines make snow to cover the hills when Mother Nature does not send it naturally, which has been happening quite often in my home state of Minnesota as of late.

The tricky part is that the snow comes out fast, and then quickly slows down and begins falling slowly (as snow does). At the end of the trail of blowing snow, the snow typically disperses in different directions and then starts falling to the ground in a snow-like way. Before, I would have not known how to control all of this with PP. But after hitting the Cow, I got some advice from Rick Gerard that introduced me to the wonderful world of PP's Layer Maps!

In short, with a custom made gradient map, you can use the different color values (e.g. different levels of gray in a grayscale map) to control different properties of your particles. So for this little project, I envisioned using a map that looks like the following to affect the speed of the snow particles as they emit from the snow blowing machine (or the "Cannon" in PP's term) in my comp.



You can almost picture it by looking at the map, but the whiter areas are the areas that will make the snow travel in the X (or to the right) direction faster, and as the map gets darker, the speed of the snow in the positive X direction moves slower. Now you can map this to many different particle properties, but we are specifically going to use this map to affect "X Speed" (explained below).

I included my map with the project files for you, but you might want to try making your own in your favorite graphics program (I used Photoshop, I also included the PSD file to show you how I composited a couple different gradients to get my final map).

If the map thing doesn't make sense yet, don't worry it will hopefully become clearer in the next step.

Open a new project in AE, and create a new 320 by 240 comp with a frame rate of 29.97. Then add a black solid to it that is comp-size, and call it BlowSnow.

Then apply the Particle Playground plugin to this solid.

Now "Import" our custom blowsnow gradient map into the project. The file I included is called 'blowsnow_map.bmp'. Once imported, drag it to the timeline and immediately shut off its visibility by switching off its "eye" icon. We do not actually need to see this layer, it is simply here for PP to use in the next step as a Layer Map.

Now believe it or not, the only thing we have left to do is to tweak settings within PP itself, so I included a picture of all my settings below for you to study. The key settings are circled in red in the picture below:

READ NOTES ABOUT PARTICULAR SETTINGS BELOW

• We want the Cannon to be located in the lower left corner where the whitest area of our custom Layer Map is located. This is because "white" will signify the greatest speed of the snow particles.
  
• We want to make sure the Cannon's direction is pointed up and to the right so that the snow is not simply being blown straight into the air, or into the ground. That wouldn't help cover the hills with snow!!
  
  
• You want to drop the Gravity Force to 50 because this affects how fast particles fall, and snow doesn't fall fast.
  
  
• After choosing our Layer Map for the Persistent Property Mapper, we arrive at the most important step of all---mapping our particle's PROPERTIES to the map itself. The color "white" includes red, blue, and green so you can use the other two available options of mapping green and blue to properties too if you wish. I mapped "green" to "opacity", so that the particles "fade" a bit as they travel from the Snow Blower. But the most important property for our project is to "Map Red to" "X Speed." To see the difference, do a RAM Preview of your project before mapping red to "X Speed", and after. You will see how the key to a realistic effect here was dependent on our Layer Map.
  
• NOTE: I also changed "Force Random Spread" under gravity (as shown in picture above) for a little "randomness" to the whole thing.

Feel free to discuss this technique in the After Effects forum at Creativecow.net.