Braking Action Medium
As has been pointed out previously, all contaminated performance is 'ADVISORY' and has not been demonstrated by flight test. These numbers are arrived by mathematical models used by the manufacturers to arrive at very conservative numbers to GUIDE you in these circumastances.
As mentioned, POOR for a braking action is a non starter.
Also, many of the Nordic/Arctic have braking actions of medium and even better when the compacted snow is covered with grit.
If you take in to account all the available data and info from pilots who have taken off or landed prior to you then you should be able to arrive at a sensible set of numbers for most situations that you will meet in your career. Just don't be first in the queue for the dawn departures!