it varies from year to year...i have gone up every April for WSI and sometimes i have had epic pow but others it was bluebird skies and skiing in t shirts. so just keep an eye on weather patterns and how this year goes. whistler is worth the trip tho especially during WSI.
i went the past two years in May, and the first year we got like 8'' of snow one night, and the second year it was pretty much typical spring conditions, but soooo much fun both times.
Went there a couple years back during the big ol' festival they have there and there was like 2 foot fresh and I was freezing my ass off. Of course, there could just be a chance it could be spring conditions (it was like about a week before we got there) but Whistler is dope neways.