Start looking for morels the first week that temperatures stay above 50 degrees overnight, usually early to mid-May. The morel season in Minnesota only lasts for about two weeks, so don't sleep! Other signs that it's time for a hike:
Dandelions begin to go to seed
Oak leaves the size of a squirrel's ear
Early spring, search on south-facing slopes in fairly open areas. As the season progresses, go deeper into the woods and explore north-facing slopes. You want to find well-drained, sandy soils and dead or dying trees (ideally with bark sloughing off the trunk). Look for these landmarks to identify potential hunting grounds:
Dry creek bottoms
Old apple orchards
Ash, aspen, elm & oak trees
But is it really a morel? Morels are always hollow. "If it's not hollow do not swallow." Morels' heads are always attached to the side. "Head attached, down the hatch!" Oh, and remember you always gotta cook 'em first... a friend's dad just got sick from eating raw morels. Happy hunting!