When sailboats are heading for cover due to 'Small Craft Warnings", experienced kayakers might want to head to the lake.
Forecast wave heights are generally reported in ranges.
At 1-2', generally forget it -- things are too tame to really get any surfs.
At 2-4', tame entertainment may be found.
At 3-5', you'll start catching some more worthwhile rides.
At 4-7', expect some sweet rides.
Above that, things start to get epic.
(See "Flow Info" tab for info on lake reports.)
DO NOT TAKE LAKE SURFING LIGHTLY! This is a whole different challenge than the river! On the river, each feature (wave or hole) is relatively 'constant' at a given flow. On the lake, every wave changes as it heads toward shore. When waves break, they can have powerful force as the weight of many gallons of water crash down on you. Having some sort of anti-implosion device for your sprayskirt is imperative at larger wave heights. Especially when waves are up, there will likely be strong currents sweeping out and down the shore. If your skirt implodes and your boat fills with water, each successive wave will hit you, making it like trying to run a class III (or higher) river with a swamped boat, but here there are NO EDDIES! Any time waves are larger than 2-3' you should not boat alone. The combination of wind and waves and currents can make self-rescue far more difficult than on any river you'll encounter in the Midwest.