Most bad weather is a clothing problem. Some of it is a reason not to start. A DNS for ice, lightning, or heat you are not prepared for protects the next race. The rain and cold guide covers training in bad weather. This page is about race morning.
Cold and rain you can still race
Dress for about 10 to 20 degrees warmer than the start once you are running. A layer you can tie at the waist beats a jacket you have never worn. Rain wants a brim more than a new shell. Shoes should already have miles in them. Nothing new on race day.
When not to start
Sheet ice on the course is a reason to DNS. So is lightning in the area if the race has not already delayed the start. Extreme heat with no plan for earlier water and a slower start is a reason to revise the goal or skip the gun. Chest pain, confusion, or a stride you cannot hold is a stop even if the weather is fine.
A DNS is a result code, not a verdict. The glossary covers what it means on the results page.