No one sits down and figures out "What do I do if there is a zombie outbreak in NYC?" from whole cloth. You use existing data and combine it. This also means you don't need to update every scenario when something changes, since you reference other reports.
Zombie apocalypse would be a mixing of riot control data & outbreak information.
Basically you marry riot control stats with medical stats + National guard response time with readiness data from their last deployment to create a graph.
My improbably scenario, the pentagon has sets of plans of what to do to deploy troops to support or suppress an armed Catalonian ceding from the republic; what level of forces are likely needed to suppress an armed revolved, what logistics they would need, the best points to deploy logistics, etc. So you take those plans, and then you modify them based on military projection reports for Israel and Iran; what sort of troop levels could those countries supply to a conflict all the way in spain, etc.
You also would want to reevaluate your plans for diplomatic situation; would the US deploying troops cause France to react?
More likely scenarios are pulled and updated, less likely scenarios are updated infrequently as bitchwork; for example, I imagine the projected response to armed revolt in Catalonia is upto date, the force projections for Israel and Iran are likely up to date.
I'm doing a fairly poor job of tying this together, but basically all the base data is there, you just take "Foreign Reponse to Catalonian Independence" and apply the force reports for "Iran invading European target" and "Israel invading European Target"
