Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 750 AM PDT Wed Apr 8 2026 ...A PAIR OF UPPER LOWS WILL BRING WIDESPREAD PRECIP TO THE REGION LATER TODAY THROUGH THE WEEKEND... ...T-STORMS POSSIBLE OVER NRN/CNTRL CA/NV IN THE AFT/EVE THE NEXT FEW DAYS... .METEOROLOGICAL CONDITIONS (WED AM - TUE AM)... An upper low sits just west of 130W offshore of nrn CA early this morning as a detatched area of 1-1.25" PW moisture has reached the nrn/cntrl CA coasts. Radar imagery shows some light returns moving into the North Bay with additional echos west of Cape Mendocino ahead of the main system. Expecting initial shower activity over nrn CA by this afternoon along with chances of thunderstorms. The low will continue to creep closer to the coast Thursday sending some more moderate precip into nw CA as troughing moves inland. The low looks to remain offshore of nrn CA near Cape Mendocino throughout Thursday and into Friday as well, gradually opening up into a trough as its surface low deteriorates. This troughing and a weakening front will spread showers further across the state Thursday night into Friday morning spreading past Point Conception and into the southern Sierra in the afternoon. Thunderstorms remain possible for Thursday and Friday mainly east of the Delta and north of the Monterey Peninsula spreading a bit further across CA/NV on Friday as the trough pushes inland. As this first system weakens, another will drop in from the Gulf of Alaska reaching the north coast Saturday morning. The arrival of this system and the continued presence of the weakening trough will keep shower activity going across much of the region as we transition between systems. A push of more moderate precip from the second system is anticipated Saturday morning first over nw CA and then spreading into the nrn/central Sierra in the afternoon as the low takes a more direct path inland. There is some disagreement on Sunday between the GFS and the ECMWF on the overall pattern, but continued shower activity is forecast through the weekend with intensity diminishing throughout. Monday, expect precip to wind down with showers over the Sierra and NV persisting as the system exits to the east. There is uncertainty in the forecast due to ensemble spread, though there is general agreement that the bulk of the precip is expected over nw CA, Shasta, and the nrn/cntrl Sierra. Looking at ensemble QPF clusters, 30% of both the GEFS and ECMWF ensemble members show pockets of the Sierra getting over 5" through Saturday afternoon while peaks in the others are closer to 1.50-3". Disagreement over nw CA as well with totals varying from 0.75" to nearly 2". Similar issues from 00z Sat to 00z Mon, though this time 44% of the ensembles favor heavier precip over the Sierra while the rest disagree more strongly on the precip over nw CA. Cluster 3 which has 21% of the overall membership shows very little precip while clusters 1 and 2 are showing 0.50-1.50". All this to say, relatively confident that a pair of lows will bring widespread precip to the region starting later today and lasting through the weekend though lower confidence on amounts. In addition to precipitation, this pattern shift will usher in cooler air bringing afternoon high temperature anomalies down from +5 to +15 deg F today and tomorrow down to near to below normal Friday. Temperatures will bottom out on Sunday with anomalies at -5 to -15 deg F. QPF this morning was a blend of the morning WPC guidance and the latest NBM. This brought totals down about 0.50-1" over srn CA and up 0.25-1" over nrn CA (even higher across the Sierra). Amounts likely will change over terrain areas in the coming days as models dial in better on the exact positioning of the lows and the subsequent orographics. QPF for the first system (through 12z Sat): 0.50-1.75" nw CA/Shasta/Sierra and 0.10-0.75" for the rest of the region aside from SE CA where little to no precip is expected. QPF for the second system (12z Sat - 12z Tues): 1-1.50" nw CA, 1-3" Shasta, 1.50-3.75" Sierra, 0.50-1" central coast/Bay Area (up to 1.50" Santa Cruz and Big Sur mountains), 0.10-0.75" coastal srn CA, and 0.30-1" down the valleys. Freezing levels 9-12.5 kft later today into tonight lowering Friday afternoon to 7.5-9 kft north of I-80 and up to 10.5 kft for parts of the srn Sierra. As the second low moves inland, freezing levels will continue to drop over the weekend reaching a min early Sunday of 4.5- 7 kft across the Sierra before lower levels spread into Monday of 4.5-6 kft. As the system exits into Tuesday, expect freezing levels to quickly rebound from west to east back up to 6.5 kft from the NV border to 9.5 kft at the central coast. 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. |