What was the destination, what was the alternate the pilot filed, what was the forecast for each airport, and how many pounds of extra fuel did they have to load?

If the forecast for the proposed destination is below certain minimums, they have to file for an alternate. There has to be enough fuel added to fly first to the destination, then fly to the alternate and still arrive with the legal minimum. That may mean adding more fuel than usual, and the extra fuel adds extra weight. They have to remove passengers, cargo, or both. Dispatch/operations makes that decision.