This trip can be made with little problem in late April as long as you schedule by the weather window and not a calendar. Also, know that it is going to be v-e-r-y cold and dress for it.
We made a trip, including a lake crossing, the second week of June last year. To give you an idea of the changes in weather, we left Traverse City with 30 kts from the SSE and made the quickest trip we had ever done to Grand Traverse Light that morning. Then we turned for Leland and spent the entire afternoon beating into 8 footers to arrive there late in the evening. Great sailing day, and because we were sailing fairly close to shore for most of this the temps were not bad. Shore temp was 85, water temp 48, boat temp in the high 50's for the most part. One great day of sailing.
Second day to Washington Island, Wi was clear, crisp, same water temp, 5-8 kts of wind, land temp on both sides in the 80's, boat temp 56.
Third day the wind totally disapeared, temp in Wi and Mi was close to 90, water temp still the same, boat temp 58, lots of fog, motored to Northport with barely a ripple on the lake.
Fourth day Northport to Traverse City, quite morning in the 80's with 5 kts of wind, boat temp 60. Arriving in TC the wind kicked up to 20 kts, and we stayed out and sailing at the base of the bay in warm temps and great wind.
In these cases NOAA was right on every day. They were wrong on the 3rd and 4th days when we started, but they corrected their forecast for reality. Kind of like TV weathermen get it right the closer they get to the storm.
We dressed in 3 layers and were fine because we planned for the cold water temps and the sun not being able to keep us warm. If we would have packed shorts and tees because of the on shore weather we would have frozen our bottoms off.
Just looked at a temp map of the north lake and most water temps are in the low 30's. It will take until July to get to high 60's.
Bottom line, be flexible enough to go with a good days weather window and dress for downhill skiing and you will be fine. All this assumes that the boat is sound for the trip.