What weight Oil do you all use in the winter in the northern states.

Will the stock Battery still crank over the engine with 10w30 in her when the temp drops below 0 ?

 

It depends on which 10w-30 you use as they don't all have equal pour points in cold weather.

As a datapoint, the pour point of the Redline synthetic 10w-30 we carry in the S2KI Marketplace is -49 F (-45 C). I can't speak to other oils but you'll be fine with that one and the stock battery.

 

0*F is -18*C. I've done experiments with 10W30 oil (dino and Mobil 1 synthetic). At -18*C, dino oil pours like molassus while the synthetic poured like it did when warm. If you have dino oil, it will still crank in extremely cold temps but it will be tough and you should warm up a bit before going too high in revs.
Typically, I've been using Mobil 1 5W30 during the coldest months in the past 4 winters. This year, I think I'll just stay with 10W30 synthetic. I plug it in if it's left outside on the really cold days.