There are many threads that discuss this. Short answer: when the internal temperature of the battery pack falls below a threshold value, the electronics start to limit max regen braking. At 10º F., you won't have any regen at all.
If you want to have regen when the ambient temperature is below freezing, try turning off Range mode while plugged in and charge your car just before unplugging it in the morning. You can also run the climate control to bring up the cabin temperature before unplugging, which saves a lot of battery power which would otherwise be used to heat the cabin when you start out.