75% of weather-related crashes are due to wet pavement, and 24% of all vehicle crashes are weather related (per Fed Hwy Admin figures
http://www.ops.fhwa.dot.gov/weather/q1_roadimpact.htm) so wet pavement alone accounts for 18% of all crashes. Add in wind, fog, timid drivers and reckless drivers. That's why I'm not sure that it's really safer on the road in a car than on the side or path on a bike. True you're more vulnerable to lightning but the odds are comparatively remote, about 50 deaths per year total from lightning compared to over 7,000 deaths due to weather related accidents. So it's logical to worry more about the traffic during severe weather than the weather itself, and getting further away from the traffic on a bike could overall be safer.