Green Lake is a great place to go kiteboarding in Whistler over the winter months.
The best season for snow kiting comes in January until early March, when the weather is cold and the lake is frozen. The wind works on the opposite principle of Squamish summer, when the sun is shining the cold air is pulled from Pemberton (North) through Whistler as it warms closer to the coast. The outflow is kiteable in Whistler during this time. Less wind is required for snow kiting than kiteboarding in the water.
It is possible to go kiteboarding in Whistler back country over the winter months as well, these spots are not easily accessible without the proper knowledge of the location or a snowmobile/helicopter. It is not recommended to head into the back country alone and without the proper gear, but rather contact a local kiter who knows the mountain to guide you to the best and safest spots.
There is no kiteboarding in Whistler over the summer months, but just 45 mins south is Squamish. Squamish brings strong consistent winds almost everyday over the summer starting as early as March/April, all the way until the end of September. The hot sunny weather creates a large temperature difference between Vancouver, Whistler, Pemberton and north, causing thermal winds pulling the cold Vancouver air north as it warms inland.
The wind is amplified by a venturi effect as it funnels through the mountains increasing the wind speed even more. The wind is generally between 15-25 knots over the summer.