5W30, 5W20 or even 0W30 shouldn't matter much (comparatively speaking) so long as you have (and plug it in) engine block heater and a battery heater blanket wrap.
A warm engine water jacket will lead to faster cranking and starting up in the midst of winter, regardless of oil weight used. In turn: faster warm up will have less oil dilution due to fuel wash down the cylinder wall during winter cold starts, your oil will last a bit longer and so should your engine.
Both your alternator and your battery will thank you for that.
Q.