By Fred Greaves GUERNEVILLE, Calif. (Reuters) – Storm-lashed California is bracing for what may be a final battering of rain and snow starting late Sunday, adding to the damage unleashed by a weather system that has caused severe flooding and killed at least 19 people across the state. Residents across a swath of central and southern California should prepare for heavy rainfall and snow, with the potential for flooding and mudslides in a region saturated after three weeks of storms, the National Weather Service said. The latest burst of precipitation is expected to hit the mountain ranges nort…