September 18, 2025 – Remnants from former Tropical Storm Mario will bring periods of showers and thunderstorms today through Saturday. There will be a short period with the potential for new fire starts tonight with isolated dry thunderstorms before the atmosphere moistens up and the risk shifts to a heavy rain threat. Currently, heavy rain potential is highest over the Sierra.
The threat for rain rates reaching debris flow thresholds is low (less than 10%), but thunderstorms that develop in the vicinity of burn scars will likely produce heavy rainfall.
Drier and warmer conditions return Sunday and Monday.
Another weather system arrives mid next week, bringing chances for showers and thunderstorms. Forecast confidence is low.
Probability of thunderstorms:
– Today: 5-20%, highest tonight south of Interstate 80 and Coast Range
– Friday: 15-30%, along Sierra/southern Cascades and Shasta County Mountains
– Saturday: 10-20% along Sierra/southern Cascades and Shasta County Mountains
– Tuesday: 10-25%, highest along Sierra
- Most likely timeframe between 11 AM and 8 PM PDT
- Potential for nocturnal showers and thunderstorms across Valley/Foothills with best chances tonight into Friday morning
- Thunderstorms will be a mix of dry and wet. Potential for both new fire starts in lower elevations.
- The threat for rain rates reaching debris flow thresholds is low (less than 10%), but thunderstorms that develop in the vicinity of burn scars will likely produce heavy rainfall.
