Based on the evidence Jordan observed, the most likely form of precipitation to fall during the night is B. snow.
At 30°F, which is below freezing, and with the presence of clouds, conditions are suitable for snow, especially if the temperature continues to drop. Dew typically forms when temperatures are above freezing, fog can form under various temperature conditions but is less likely given the specific temperature in this scenario, and rain would more likely occur above freezing temperatures.