The annual guessing game of whether fireworks will be fully visible in San Francisco has started with forecasters saying Friday that low clouds and patchy fog are expected to roll over the Bay just when the pyrotechnic extravaganza is set to go off Monday night. While it’s still unclear what kind of view the skies will offer thousands of spectators for America’s 240th birthday bash, Bob Benjamin of the National Weather Service predicted that the fireworks would likely end up just below the cloud cover. The conditions in San Francisco could be similar to last year when The Chronicle reported the sky “was shattered by colorful explosions of light, often shrouded by low-hanging clouds.” Holiday revelers in the North Bay at fireworks shows like the one planned at Sonoma County Fairgrounds in Santa Rosa shouldn’t fret: clear conditions are predicted for Monday night.