the first time my bike quit running during a snowstorm, i'd assumed snow/slush got sucked up into the carb.
today, there wasnt snowfall from the sky and it quit.
my father-in-law is a airplane mechanic, and this is what he told me:
the gas in the carb is already cold. during extreme cold, it can evaporate (making carb even colder) and the remaining moisture will amass in the venturi. so...plugged jets.
with the bike still outdoors, we took a heat gun to the carb and after a few minutes it started right up.
he said HEET or other gasoline dryers (methyl alcohol) should do the trick.