This comes just a few days after the remnants of Tropical Storm Mario brought a surge of moisture into Southern California and parts of the Southwest, resulting in deadly flash flooding. Southern California, in particular, doesn't typically see much rain during September. The highest potential for flash flooding in parts of Southern California will occur Tuesday and Wednesday, with the heaviest rain falling over the Central Valley and eventually the Sierra Nevada range. Similar to the weather pattern last week, this system is also drawing in tropical moisture from the Pacific Ocean around Mexico. REMNANTS OF MARIO TRIGGER DEADLY FLASH FLOODING, MUDSLIDES AS RAIN SURGED ACROSS SOUTHERN CALIFORNIAThis graphic shows the flash flood threat for California and the Southwest.