What are the operating temperatures of rollercoasters at the park? I assume there is a minimum temperature but I'm not sure there is a maximum?
I've not come across a maximum operating temperature stated by a park, but minimum operating temperatures are by some. Silver Dollar City lists their B&M having a minimum operating temperature of about 4.5c
Minimum temperatures have a greater impact to whether a roller coaster can operate, typically because they will run slower and have a greater chance of not making it around the circuit. The slowness comes from the wheels becoming more brittle and oils not working as effectively. Another issue in the cold weather is that the hydraulic systems operate less efficiently and in the extreme case will cause friction brakes to not operate properly.
At higher temperatures, all of the mechanical systems work much better, with the rides operating faster and the brakes more responsive. In terms of a maximum temperature, polyurethane wheels used in industrial systems that appear somewhat similar to roller coaster wheels, are rated to maximum temperature of around 88c. Of course, the stresses put on roller coaster wheels may reduce this and that figure isn't air temperature but rather the wheel temperature, which will be significantly higher. Other technical issues coming from higher temperatures can include rides operating faster than the sensor systems are happy with, increasing the chance a sensor brings the ride to a halt. This can come from either the system being unhappy with the speed the train travels, or the vibrations it causes to the track at those speeds.Then there is the human side. Higher temperatures mean more chance of guests becoming ill from not drinking enough or standing too long in the sun, causing ride shut downs. The warm weather also brings out greater crowds, with more people increasing the probability someone does something to cause the ride to stop, such as trying to take their phone out and film the ride.