Happened last year too. 
it is cold, like below freezing. 
the garage smells like gas; no obvious fuel leak. Ideas?

I had a similar situation and discovered that the charcoal canister had liquid gas in it.  Turned out that the plastic valve on top of it was cracked which prevented purging of the stored vapors.  Glued the valve back together and no more gas smell.

So you might check the canister and the purging system.  Might just be a cracked hose.

Yup! Same thing for me. The vapor canister cracks because of age. I also recommend you check that.