Subj : Flood potential Calif To : All From : Mike Powell Date : Mon Nov 17 2025 09:35:04 AWUS01 KWNH 171014 FFGMPD CAZ000-171600- Mesoscale Precipitation Discussion 1227 NWS Weather Prediction Center College Park MD 514 AM EST Mon Nov 17 2025 Areas affected...portions of northern and central California Concerning...Heavy rainfall...Flash flooding possible Valid 171001Z - 171600Z Summary...A stout mid-level wave west of Eureka was prompting scattered shower and thunderstorm activity across a broad part of northern and central California. These trends will continue for the next few hours, and areas of 0.5-0.75 inch/hr rain rates are possible. A few instances of flash flooding could occur in sensitive areas and near burn scars. Discussion...A vigorous mid-level wave was providing ascent for several areas of convection 1) just west of Eureka over open Pacific waters and 2) along an axis from Redding south-southwest to near Monterrey. Over the past hour, more robust convective activity (with lightning) developed near/south of San Francisco and moved inland. Both of these regimes were responsible for areas of 0.5-0.75 inch/hr rain rates. The Redding/Monterrey convective band was being forced by a strong front moving southeastward across the region. PW values of 1 inch along and ahead of the front near the coast was aiding in the heavier rain rates. Over time, as the aforementioned front shifts southward across the state, strong upslope flow will aid in continued moderate to heavy rainfall and a few instances of flash flooding especially along upwind areas of the Sierra. The front will also aid in occasional bursts of heavier rainfall along coastal areas from Monterrey southward toward the Transverse Ranges/Santa Barbara County through 16Z/8a Pacific time. Sensitive areas/burn scars could experience another round of debris flows and excessive runoff. Another more conditional risk for heavier rainfall will occur near the center of the mid/upper trough near Eureka. Slow-moving convection was being supported by ascent from the trough and very cold temps aloft (-20 to -24C @ 500 mb). Heavier rainfall could occur between Eureka and Santa Rosa. Flash flooding is also possible with this activity. Cook $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .