Complex sentence: The Almanac is most famous for its long-range weather forecasts, which it claims are 80% accurate; however, these forecasts have been shown to be at most 2% more accurate than random guesses.
Split into simpler sentences: The Almanac is most famous for its long-range weather forecasts, which it claims are 80% accurate. However, an analysis discovered that these forecasts are at most 2% more accurate than random guesses.