I've been commuting in upstate NY for the last couple of years. I carry my laptop and stuff inside an Osprey 34L Radial pack https://www.ospreypacks.com/us/en/pr...-RADIAL34.html

Even with the worst rain, my stuff is always dry. And it has lots of neat features for cycling such as a u-lock compartment and a helmet holder. It is a wonderful pack. I strongly recommend it.