Beautiful day of sailing on Lake Granby, Co. Light, 5 kt wind until about 1 PM. I had been watching a darkening buildup to the north about 5-10 miles away. Seeing some rain coming out of the bottom, I said to myself, huh.. that's virga. I am usually very leary about tstorms on that lake because they can really build up in a hurry, and normally call it a day when they form. I was single-handed and had just the full main up and close hauled when in a matter of less than a minute the wind suddenly blew up. And I mean really blew up. The waves went from ripples to about 5-6 feet with streaming, frothing whiecaps. I would guess about 30 kts of wind. Being by myself, I could not drop or reef the main. I just kept the main sheeted in and kept the boat feathered into the wind, but the gusts were still putting the rail in. After what seemed like an hour of this, but was probably only 15 minutes, their was a lull and I quick like a scared bunny got the main down. The wind actually was not still satisfied and roared back again while the boat rocked around like crazy until it finally quit and became almost dead calm. Total time of this event was about 30 minutes. This is my first year sailing my new to me 23.5 and it made it through. It never rounded up and showed me how much it could heel. Not that I want to do that again. It also will cause me to head for my anchorage whenever I see any kind of a suspicious storm near Lake Granby. It's a beautiful lake at 8500 feet and I think it is the best sailing lake in Colorado. What would you have done??