How Cold is Too Cold?
The question might sound valid, but anyone who knows the outdoors knows that there is no bad weather, there is only a lack of proper gear.
Selecting the Proper Gear
Whatever the temperature range you might be in in your adventure, make sure to do your proper research before heading out. Not every sleeping bag is rated the same, and not every type of material behaves the same once it either gets wet with sweat, or water. Consider the differences between wool, cotton, and polyester. Wool retains the insulating power when wet, while cotton looses almost all of it. Polyester behaves more like wool does when wet and is also more comfortable. If you have given educated decisions to your gear, and its properly rated, you should have no trouble in keeping warm even in the winter, especially if you can keep out of the wind, and can keep a small fire nearby.