iPhone location signal duration in snow, no charge?

Cold decreases the capacity of the battery. There is no exact formula for predicting the length of time it will maintain signal. From my use of lithium ion batteries in cold climates like Montana and Yellowstone National Park I would estimate no more than 6 to 8 hours, maybe more, maybe less depending on temperature fluctuations, exposure to sunlight (warmth) etc.

If an iPhone is completely out of charge and not connected to a network, it won't be trackable. Under better weather conditions, if a phone which isn't charged comes near another iPhone it can momentarily leave a signal, but if your iPhone is buried under snow in extreme cold, not powered on nor connected to a network, it won't likely come close enough to another iPhone or even be able to communicate with one.

If your phone is indeed in snow, this is not likely going to have a good outcome for you. Once the snow starts to melt, the phone will take on water and water destroys phones. Apple won't attempt a repair on an iPhone damaged by liquids.

See what Apple recommends if your phone is lost --> https://support.apple.com/en-us/101593

If it was stolen --> https://support.apple.com/en-us/120837

If it's dead, it won't be broadcasting its location. I would do as Jeff suggests and look in and around in your car carefully. I too have managed to drop my iPhone in my car and found it under the seat.

If the battery is completely dead, it doesn't matter where it is, you won't be able to track it electronically.

Retrace your steps and look for it the old fashioned way.

Did you search your car good? Check between seats, under seats, door pockets etc. I’ve found many an iPhone between the seat and the console too many times to contemplate. Good luck !