Question - when people talk about the "weather window" how much time are we realistically talking? I've heard that the weather service on Lake Michigan can be unreliable and it's a rare day that there isn't at least a slight chance of storms in the area. Do you rely on the weather service or are you just keeping your eyes on the sky? If the latter, when you decide to run for cover? At the first sight of storms or something else?
True enough, the NOAA radio forecast almost always states a chance of showers and thunderstorms. I'm less worried about thunderstorms and squalls then I am about heavy seas. You can reef, drop sail, forereach, run, etc. in temporary high winds, but sustained winds make the seas build. The sometimes short and steep waves of the Great Lakes can put a beating on you.
"Weather windows" can last for several days at a time, in which case you'll likely need your motor as often as you'll need your sails on northern Lake Michigan. Sustained high wind events seem to typically last 1-3 days and can take only a few hours to make the waves uncomfortable for a small boat.
I pay most attention to sustained wind patterns and predicted wave heights. I use a combination of intuition, NOAA weather radio, buoy data, and services like SailFlow
to determine what the weather is going to do.
You'll start to pick up on normal patterns, such as the typical pattern in my homeport on L. MI of offshore winds in the morning/evenings, slack wind midday, and often moderate onshore afternoon breezes. Sometimes when we're cruising we are able to take adventure of early morning sailing, etc.