Hydrometeorological Discussion National Weather Service / California-Nevada RFC / Sacramento CA 740 AM PST Thu Nov 12 2026 ...DRY CONDITIONS THROUGH THIS EVENING AS HIGH PRESSURE REMAINS IN THE AREA... ...CHANCES FOR HEAVIER MORE WIDESPREAD PRECIP FRIDAY THROUGH EARLY NEXT WEEK AS A PAIR OF SYSTEMS MOVE THROUGH... .METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - WED AM)... The ridge that has been drifting overhead the past few days continues to exit the region to the east as a trough approaches from offshore. This system will head south/southeastward offshore before closing off into an upper low later today. As that low moves towards soCal/Baja a larger upper low will approach from the Gulf of Alaska sending a front into northern CA. Initial showers from the larger low set to reach the nrn CA coast late tonight while showers from the southern system impact the soCal coast. More moderate precip to move onshore to the northern CA coast Friday morning before spreading into the Bay Area, central coast, and the Sierra by the afternoon. The GFS is still lagging behind the ECMWF on the movement of the front/precip similarly to yesterday. As the front carries precip further into CA, troughing from the parent upper low will also push onshore into nw CA tomorrow swinging inland west to east. This will keeping precip chances going across CA the rest of the day. Lighter more scattered showers then expected on Saturday as we transition between systems. Models have backed off some on the precip amounts compared to yesterday, REFS hourly exceedance probabilities for higher rain rates have lowered with 0.50"+/hr rates along the north coast now closer to 20-30% with higher probabilities (60-80%) over Shasta and other mountainous areas. Ensembles remain well aligned on focusing heaviest precip along the nrn CA coast, Shasta, and across the Sierra. 48 hour totals ending 00z Sunday over these areas range from about 1.50" to over 3-4", so still some uncertainty there. Another upper low will send an additional front into the west coast on Sunday bringing the next round of more widespread precip to the region. The GFS continues to lag behind the ECMWF timing wise by at least a few hours, but both agree on precip reaching the north coast some time Sunday morning. This time the parent trough will dig further south offshore before it starts to move inland. The front will push through the Bay Area focusing on the central coast and central/southern Sierra by mid morning Monday. The trough will then shift inland as it stretches across the entire state late Monday into Tuesday. Most of the precip at this point will be south of I-80 as the core of the system focuses over central/southern CA. There are still additional differences between the GFS and ECMWF on the placement and depth of this system. The ECMWF has it closing off into an upper low beginning to move into AZ late Tuesday afternoon while the GFS keeps it an open trough lifting more northeastward through NV into the Four corners. The storm door looks to remain open after that as another upper low descends towards the area from the Gulf of Alaska. The continued timing differences between the GFS and ECMWF create uncertainty as to when this next round of precip will arrive into nrn CA. This time the GFS is the quicker model carrying precip from the next front into nrn CA Tuesday evening while the ECMWF delays until the late overnight period. Either way, the weather should remain active through at least mid next week. QPF has gone down since yesterday as models backed off on amounts some. Highest totals still expected along the north coast, over Shasta, and across the Sierra. QPF through 12z Weds: 2-4.50" Sonoma County northward along the coast (4-5.50" Smith Basin/King Range), 2.50-5.50" Shasta, 1.50-4.50" Sierra, 0.75-1.50" Bay Area, 0.50- 1.25" central coast (up to 2" Santa Cruz mountains and Big Sur coast), 0.25-1.50" down the valleys (up to 2" closer to the foothills), and 0.50-1" coastal soCal. Freezing levels to lower tonight down to 7.5-9.5 kft across most of CA tomorrow morning reaching a minimum in the evening of 5.5-7.5 kft for nrn and most of central CA before rising again as the system exits. The next system on Sunday should re-lower levels from nw to se with most of the region down to 4.5-8 kft Monday night. Please Note: This product may NOT be routinely updated. Please refer to the following product issued by the CNRFC www.cnrfc.noaa.gov/Daily-Briefing for a graphical summary of weather and hydrologic conditions. |