global proc addExprForSnow()
{
//select particle transform or shape node
string $particleName[] = `ls -sl`;
string $particleShape[] = `pickWalk -d down`;
dynExpression -s "float $windSpeedMag = windSpeed + windSpeed * cos(time * 0.1);\r\nvector $windSpeed = <<windDirectionX, windDirectionY, windDirectionZ>> * $windSpeedMag;\r\nvector $vel = globalSize * rot( dnoise ( (position/turbulenceSize) + <<phaseX, phaseY, phaseZ>>) , (<<windDirectionX, windDirectionY, windDirectionZ>>), time);\r\nvector $vel2 = globalSize * dnoise(position/(turbulenceSize*2) + time * 0.5);\r\n$vel = $vel * twirlTurbulenceStrength + $vel2 * noiseTurbulenceStrength + ($windSpeed*globalSize);\r\nvelocity += $vel;\r" -rbd ($particleShape[0]);
}

addExprForSnow;