Hey Stray:
I don't know of a website that gives a forecast for barometric pressure but you can get a real good idea of what to expect by looking at these four pages on weather.com:
Current Surface Weather - http://image.weather.com/images/maps...wx_600x405.jpg
You can see where the low-pressure areas - Red "L" - and high-pressure areas - Blue "H" - are.
Then you can see where the lows and highs are forecast to go in the next 24-hours at:
http://image.weather.com/images/maps...st_720x486.jpg
http://image.weather.com/images/maps...st_720x486.jpg
http://image.weather.com/images/maps...st_720x486.jpg