Heat from California’s Creek Fire is creating dangerous thunderhead clouds rising over 45,000 feet high. The wildfire has already scorched 152,833 acres in its four days of burning through the Sierra National Forest. It’s been generating weather, which is in turn is fueling its growth. SNIP These wildfire-created thunderhead clouds, or pyrocumulonimbus clouds, occur because the fire-heated air rises and carries water vapor up, causing the thunderheads. Common sense would suggest rain clouds would help firefighters knock down the blaze.