Numbness over dorsum of left hand; over thumb and area below index, middle and ring fingers down to wrist- 1 day. no pain, non progressive, unilateral

Radial nerve: The radial nerve supplies sensation over the back of the hand and extensor muscles of the forearm and hand. Numbness or weakness can occur from sleeping on the arm in an awkward position (saturday night palsy). The numbness should resolve. If it persists or symptoms worsen seek an evaluation with a neurologist.

Radial sensory nerve: Dorsal radial sensory nerve supplies that area could be too tight a watch or bracelet causing pressure on the sensory branch at the wrist level. Could also be a traumatic blow to that area, usually neuroapraxic injury(bruising) that will respond to rest and time.

Possible radial nerv: You are describing an area of skin supplied by radial sensory nerve although usually it is typically over 1st. Web space.