snippet.js

$(document).ready(function() {
  
  $.fx.interval = 24;
  var $flakes = $('span.flake'),
      rand = Math.random,
      ceil = Math.ceil,
      windowWidth = $(window).width(),
      land = $(document).height() - 295,
      multipliers = [5,6,8,12,16],
      mLength = multipliers.length,
      randomIndex = function() {
        return Math.floor(Math.random() * mLength);
      };
      
  
  var fallingSnow = function(elem, opts) {
    var $flake = $(elem);
    $flake.css({
      top: '-40px',
      left: function() {
        return ceil(rand() * (windowWidth - opts.flakeWidth));
      }
    });
    setTimeout(function() {
      $flake.animate({top: land + 'px'}, opts.speed*multipliers[randomIndex()], function() {
        fallingSnow(elem, $flake.data('options'));
      });
    }, opts.timeout*multipliers[randomIndex()]);
    
  };
  
  $(window).bind('load', function(event) {

    $flakes.each(function() {
      $(this).data('options', {
        speed: 1500,
        timeout: 250,
        flakeWidth: 20
      });

      fallingSnow(this, $(this).data('options'));
    });

  });
  
});