A few comments:

Just yesterday I was a pax on an AA 757 that diverted to DTW enroute between MIA and ORD. We were out of gas. The Capt said he put on 40" of extra fuel, on top of his flight plan, and burned through all of that...had to fly all the way to DCA to get around a line of weather.

I had a flight, no alternate required, forecast at the destination was CAVU for about 48 hours...area forecast also good. Unforecast heavy fog in the whole OH River valley...had to divert due to fuel issues.

Had a flight PVG-SYD. Dispatcher put 48 tonnes (106K lbs) of contingency fuel on due to typhoons in the route of flight. We didn't use very much of that fuel.