Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 830 AM PST Sat Feb 8 2025 ...MAINLY DRY AND COOL OVER THE WEEKEND INTO MONDAY EXCEPT LIGHT PRECIP POSSIBLE OVER NW CA AND SRN OR CASCADES TODAY... ...LIGHT PRECIP POSSIBLE TUESDAY THEN MORE WIDESPREAD PRECIP POSSIBLY MODERATE TO HEAVY AT TIMES MID-LATE NEXT WEEK... .METEOROLOGICAL CONDITIONS (SAT AM - FRI AM)... Upper level shortwave trough moving through the Pac NW and brushes far Nrn CA and Nrn NV today. Scattered showers with amounts generally less than a quarter of an inch along the NW CA coast and Srn OR Cascades and possibly a few hundredths into NE NV higher terrain today. Freezing levels generally near the surface this morning then rise to around 2500-3500 ft near ORCA border and around 4500-5500 ft for Nrn Sierra and NE NV this afternoon. A weak broad trough digs into the region Sunday into Monday with northerly (NW- NE) flow and dry conditions expected. Max temperatures generally below normal up to 15 degrees except near normal SE CA and far Srn NV this afternoon and generally below normal up to 20 degrees (in the north) below normal and near normal to a few degrees above normal for far Srn Ca on Sunday and generally near normal to 20 degrees below normal over the region on Monday. Min temperatures 5 to 20 degrees below normal over Nrn CA and below normal up to 15 degrees for Central CA and most of NV and near normal to around 10 degrees above normal for Srn CA (especially La and to the SE) tonight. For Sunday night and Monday night, min temperatures 5 to around 25 degrees below normal over Nrn CA and 5 to 15 degrees below normal for Central CA and NW NV and near normal to 10 degrees below normal for Srn CA (except far SE CA up 10 degrees above normal Sunday night) and Srn and Eastern NV. The pattern turns wetter for mid-late in the week with low pressure system that taps into moisture plume but still a lot of uncertainty due to differences in timing and track of system and moisture between models and ensemble members. Light precip is possible on Tuesday then becoming more widespread with periods of moderate to heavy precip at some locations Wednesday into Thursday. The forecast for Tuesday with a mix of latest NBM and WPC and some previous forecast brings mainly light precip along the Northern and Central CA coast (up to a quarter of an inch) and into the Shasta Basin and down along the Sierra and into portions of NV and possibly a hundredth or two to Srn CA mtns. The deterministic 12Z GFS and the 00Z EC and the 00Z Ensemble mean bring heavier precipitation farther south into Srn CA and the ensemble members vary how much precip and if reaches all the way to the Mexico border. The 24 hr QPF 50th Percentile clusters ending 00Z Thursday show 55% of the Ensemble members (Canadian 40% GFS 70% and EC 52%) only light to moderate precip for Nrn CA coast and San Diego Cty Mtns and dry elsewhere and about another quarter (26% of total ensemble members- Canadian 50% and Gfs 20% and EC 20%) show moderate to heavy precip far as snow levels, they will start out near 5000-6000 ft Wednesday morning, climbing to over 7500 ft during the day Thursday in warm air advection ahead of the trough before falling to around 5500 ft Friday afternoon and down to around 5000 ft Friday evening as precipitation tapers off over Nrn and Central CA and lighter precip over NV and the other 19% (Canadian 10% and GFS 10% and EC 28%) show moderate to heavy precip over Central CA coast into western transverse mtns ans Srn Sierra. The 24 hr QPF 50th Percentile clusters ending 00Z Friday generally all show precip across most of the region except far SE CA and possibly Srn NV (in 31% of total members) but vary widely in amounts and areas of heavier precipitation. The EC dominated cluster (31% of total- Canadian 10% GFS 13% and EC 50%) has the highest precip amounts and spreads them over the transverse mountains. the GFS dominated cluster 38% total member Canadian 35% GFS 60% and EC 38% have lowest overall amounts and highest precip amounts farther north along Central CA coast and Srn Sierra. The Canadian dominated cluster (total 31%- Canadian 55% and GFS 27% and EC 24%) has the heaviest amounts farthest north over Northern CA and along the Central CA coast and Sierra. The forecast for Wednesday brings around 0.75-2.5 inches along Nrn and Central CA coast and 1-2 inches over the Sierra and Shasta Basin and the Santa Ynez Mtns and 0.5-1 inch for Sac Valley and 0.1-0.6 for SJ Valley and 0.25-1 inch for Srn CA coast into Mtns. Precip amounts in the current forecast for Thursday are generally 1-2.5 inches for Nrn CA coast and Shasta Basin and 1-4 inches for the Sierra and Central CA coast and 0.5-1.5 inches for Central Valley and 1-2 inches for Srn CA coast and 2-3 inches for the Srn CA mtns. These amounts will change as the system gets closer and details become clearer. Freezing levels on Tuesday around 1000-2000ft near ORCA border and 3000-5000ft along the Sierra and Nrn and Central Nevada and drop to around 5000-1500 ft near ORCA border Wednesday morning and 2000-4500 ft along the Sierra and 1500-3500 over Nrn and Central NV. Cold air trapped in some locations (esp valleys) may bring lower snow levels to start. Rising freezing levels with warm air advection on Thursday to around 4000-5000ft near the ORCA border except around 3000- 4000ft for Shasta Basin and around 5000-8000 ft (N-s) for the Sierra and 4000-7000 ft for NV and around 8000-9000 ft over Srn CA. |