Yes, Pennsylvania Black Slate can be used for exterior applications in cold climates in the United States. Black slate is a durable and weather-resistant material that can withstand freeze-thaw cycles and harsh weather conditions. Pennsylvania Black Slate, in particular, is known for its ability to resist cracking and fading in extreme temperatures. However, it is always recommended to consult with a professional or slate supplier to ensure proper installation techniques and maintenance procedures are followed for optimal performance in cold climates.