Kristen, a discrepancy in the barometric setting between an airport's weather station and an airplane's altimeter will cause the altimeter to be off by 100 feet for every tenth of an inch in mercury, or 1,000 feet for every inch.
Sometimes, as did happen to me last week, a controller will call attention to the barometric pressure as a gentle reminder to a pilot to check that their altitude agrees with the intended flightpath. A few seconds into the attached clip the controller repeats the Omaha barometric pressure to me. I declared that I had "Information November" in my initial contact with Omaha Approach, which is code for: "I have the latest weather report from Omaha", so there was no need for him to tell me the current weather. However, I stated in our conversation that I intended to avoid entering Omaha airspace (which has a floor of 2,500 feet in the outer perimeter), and according to his radar screen I hadn't started my decent yet, so he wanted to remind me that I was about to enter the airspace. Stating the local altimeter is a very polite way to say, "check your altitude."