Driving from Alta to Heavenly

Hi all..

I am going to be skiing at Alta/Snowbird on the 6th and 7th of December,
then driving on the 8th to Heavenly and skiing there for 2 days... Map point
says that it will take about 9 hours, which is fine..

However, what I didn't realise is that this motorway is pretty "high" (asl)
and it seems to snow there.. my question is, how likely is the highway to be
closed, and if it does snow and stay open, how much will this affect my
journey?

Also, I'm hiring a car in LA (we're doing a 3 week trip going out as far as
SLC) and I need to get some snow chains. Just need them to last three
weeks.. anyone got a suggestion about where to buy some cheap ones?