As soon as you exit your farm on the day of the festival (footage: Year 1 spring potluck), the festival pamphlet will appear. It disappears as soon as you re-enter the farm.
#Festival Pamphlet Appearing Randomly
tawdry cedar
sterile karma
This is actually a new feature. They made it so pamphlets show once you're off your farm, to try to remind you of the festival as well as it's location.