By September, Fall has completely settled in Scotland. Average temperatures are in the mid-40s (F) to upper 50s. In terms of rain, it's Scotland so there's always a chance. In terms of packing, it's best to pack layers. This way, when you enter a pub, restaurant, or museum, you can peel off clothing and be more comfortable. Make sure you have gloves, a warm hat, a scarf, and of course, a rain jacket.