“The captain has switched on the ‘fasten seatbelt’ sign.” If the sheer thought of turbulence is triggering panic and nausea in you, then one website might help calm your nerves before a flight. Turbli.com offers a kind of weather forecast for airplane turbulence: You enter your departure and destination airports and see how rough the flight is likely to be. The website, which is completely free, gives you a graph of the flight’s predicted turbulence from take-off to landing, while also giving a forecast of any delays that headwinds might cause. The site has a map of turbulence around the world…