Outdoors in the thirties can cause hyperthermia and death
Sure, temperatures in the 30s can kill you eventually, if you're (a) wet; or (b) dressed far too light.
I don't know where you're from. I grew up in the upper Midwest. Temperatures in the 30's are balmy. When we start talking -30s (Fahrenheit), it's time to take them seriously. -30 can kill even if you're dry and fairly well-dressed.