It's not ambiant air temperatures, it's the water heater doing it's job of heating water.
If there is a closed system, like a check valve in the system, and the water is heated in the tank, then an expansion tank will be needed.
For the Arizona California region. Where the temperature is between 39 - 102 degrees F,
do you need a thermal expansion tank.
Thermal expansion occurs when water is heated by the water heater. This expansion needs somewhere to go or the pressure within the heater will rise high enough to trip the T/P valve. In an open water system, meaning no check valves such as found in a pressure regulator and/or some water meters, the expansion is easily absorbed by the city water main. The actual volume of water is quite small, but as you probably know, water does not compress. so the expansion tank provides a temporary home of this water.
Many local water utilities are swapping water meters to one with a check valve...so, you may not NEED one now, they could change the meter tomorrow during maintenance, and then you would. The volume you 'push' back through the meter is often only a cup or so, but the utilities switch to check valves is to prevent water that came in from going back out since it is possible you polluted it. It protects all of the other customers. Now, while it can happen and has, it doesn't happen often. But, adding the check valve gives one extra layer of protection to the system, so they're often doing it. It doesn't 'hurt' to have one, but unless a closed system, you don't need one.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013