Although, there is no way to perfectly predict what the weather conditions will be, in general the seasonal sea and air temperatures behave in predictable ways.  The lake remains cold for most of the spring and the lake air temperatures tend to reflect this.  In spring, the further offshore you go, the colder the air temperature.  In June it is not uncommon for it to be 80 at the dock and 60 two miles out.  As the summer wanes the lake hits its hottest temperatures, with the river being around 80 and the lake around 75.  This extends out into September and it is not uncommon for the land air temp to be 60 and the lake air temp to be 70.  The lake also releases it's heat after the sun goes down and a breeze often blowing over the water at night in the late season will be pleasantly warm.  Given the range of temperatures that may be experienced, it is always best to dress in layers, even when the air temp on shore is warm.  Mid-season a T-shirt and a sweater are usually more than enough but at the extremes of the season, you can go from T-shirt weather to jacket hat and gloves weather during the same sail.  This is most true early on in the season.