I am currently developing a sensor box and plan on running it outside. Temperatures can get as low as -40 degrees F and once my box reaches an internal temperature of 32.18 degrees F it fails to read the sensors attached to the Raspberry Pi. Now the Raspberry Pi board still works, and records nothing once the temperature dips below 32.18 so I am wondering if the GPIO pins have a minimum temperature range of operation or if it's a component on the Pi board that is causing this. I am stumped and would really appreciate the help here. Thanks.
From a discussion on the RPi Forums, the operating range is -25C to +80C, -20F is -28C, so you are outside of the operating range.
I have noticed this with my Pis too (I'm in Canada and they are in the garage), I use a lightbulb to warm up the box that the pi is housed in so it survives.
Given that the concern here is about the temperature of the pi being too low, the logical answer in this situation is to provide sufficient insulation to allow the pi to keep itself warm under these environmental conditions. Then retest the external temperature sensors.
Don't add too much insulation because the pi may then overheat and to this end you may find it useful to measure the temperature of the SOC as well as the external temperatures of interest. You may also want to make sure the box is suitably waterproof if the outside becomes warm enough to melt any surrounding ice.