One I have learned to believe in is: If you see a terrapin crossing the road, expect very heavy rains within three days.
It is based on the fact that terrapins cannot swim, where turtles can, and therefore, when it rains terrapins will drown if they do not leave the low areas in which they tend to leave. So they apparently evolved with the ability to feel the pressure changes and/or in some other way can sense when a weather system which has the potential for very heavy rain is approaching.
Now, turtles will also be seen crossing roads, but that does not necessarily mean rain. It is simply circumstance that a terrapin is crossing a road. They do often live in side ditches, therefore the closest high ground would be the road. But wherever they live, terrapins will move up and out of the low, cool, damp area where they tend to live, to higher ground when heavy rain is on the way.
Just my opinion.