Low pressure off the West Coast will draw tropical moisture northward through the end of the week, leading to scattered showers and thunderstorms at times. Moisture is on the increase already today, with the latest sounding showing pw's at nearly 200% of normal with decent instability. This should support scattered showers and thunderstorms over the mountains and deserts through this evening, some could drift to the west over our valley areas. Warm and humid with highs in the mid-70s, south-southeast winds 5-10 mph. Deeper moisture will arrive tonight into Thursday, with widespread showers and thunderstorms spreading over much of Southern California. This will likely be a stratiform-type event with overcast skies and light to moderate rain, occasionally heavy with embedded thunderstorms. Some storms may contain heavy rain with strong, gusty winds, frequent lightning, and small hail, producing localized areas of flooding, where a flood watch is in effect for many locations through 2:00 AM Friday. The deeper moisture will lift north of the area on Friday, though lingering moisture and instability will continue to generate scattered showers and thunderstorms. Cooler with highs in the 60s as lows drop into the 40s, winds light & variable, except gusty near any storms. Diurnally driven convection will remain confined to the mountains and desert over the weekend as moisture continues to decrease through early next week. Another tropical system is developing off the coast of Mexico and will be watched for potential influence on our weather later next week.