Sometimes Marquette gets a lot of snow all at once. This can be problematic if you have to park your car outside for an extended period of time. Say for example you are flying out of the airport, and you want to leave your car. There's no parking garage! In the winter, it's always a question whether you'll be able to find it when you get back. Maybe you should attach a colored ping-pong ball or flag to your antenna? (Unfortunately, a lot of cars today don't have antennas.) One year I went to Florida for a week in March, and this is what I found when I returned. (Be sure to carry a shovel in your car.)
In the U.P. there is always the possibility of mosquitoes and biting flies any time of the year except winter. When out and about, especially if hiking, have insect repellent available in case you meet some of these not too pleasant residents. Also while hiking keep alert for black bears.
Though it may look very tempting and within reasonable distance to reach from the beach, NEVER attempt to swim out to the "Picnic Rocks" on the north side of Shiras Park beach, the parking lot turnout along Lake Superior where Fair Avenue and Lakeshore Drive intersect. This area is notorious for strong currents despite the short distance, and many people have drowned here. There is a large warning sign present, as well as a memorial recently constructed to remember those that drowed here.
Do I have to tell you this? Avoid walking on the breakwalls when there are high waves - or when there is a storm approaching. Every few years someone gets swept off and drowns. Last time it was two students at the university here. They didn't believe that Lake Superior could kill them. Ach. Do use common sense and caution when swimming in the Lake. It can look calm and inviting, but there can be dangerous 'riptides' that you can't see from shore.