96 Cougar win't start when weather cold

96 Cougar 3.8 won't start when temperature drops below about 50 degrees. Engine just cranks. When weather warms up, car starts and runs great. Been getting progressively worse. Any ideas where to start troubleshooting? Thanks.

coolant temperature sensor?

First you will have to determine if you are not getting fuel or spark and start from there. Since a cold engine requires more fuel I would look at fuel pressure and flow.