####018005149#### AGUS76 KRSA 012145 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 130 PM PST Fri Mar 1 2024 ...WIDESPREAD PRECIP AND MOUNTAIN SNOW INTO THE WEEKEND WITH A COOL TROUGH MOVING INTO THE REGION... ...ADDITIONAL PRECIP CHANCES NEXT WEEK... .METEOROLOGICAL CONDITIONS (SHORT TERM: FRI PM - MON AM)... Upper level trough deepening and approaching the west coast with an upper/sfc low approaching the B.C. Pac NW coast this afternoon then moves onshore tonight into Saturday as low weakens off the B.C./WA coast. One Cold front around Pt Conception an NE through the Srn Sierra and into NE NV. Another front is around Pt Arena and into the Srn OR Cascades. Showers and isolated thunderstorms moving through Nrn and Central CA and Nrn NV and Srn OR and light precip around Point Conception to LA county this afternoon. Precip will continue this afternoon into Saturday with the most precip expected over the Sierra with abundant snowfall. Precip will taper off Saturday night into Sunday. Little changes to the forecast with the biggest changes to increase amounts along the Central CA coast and transverse mtns and Srn Sierra this afternoon into the day Saturday. Precipitation amounts through the weekend are generally 3-9 inches for the Sierra and 1.5-4 inches along the Nrn CA coast and 1-3.5 inches Shasta area and Central CA coast and 0.5-2 inches with up to 3.5 inches over mtns Srn CA coast Point Conception-extreme SW San Bernardino county and 0.1-1.25 inches for Orange Western Riverside and San Diego Counties. Thunderstorms possible over Srn OR and nrn and Central CA and into far western Nevada today and more confined to the the coast and into the Central Sac and Nrn SJ Valley on Saturday. A few strikes this afternoon already over nrn CA and more off the NrnCA coast. HREF exceedance probabilities are about 10-50% for 0.50"/hr rainfall rates for CA, especially over the Sierra, into Saturday afternoon. Max temperatures around 5 to 15 degrees below normal for most of CA and near normal to 10 degrees below normal for SE CA and NV today drop to around 5 to 20 degrees below normal for Saturday and Sunday. Overnight temperatures near to around 10 degrees below normal for Srn OR and Nrn CA and near to 10 degrees above normal for Central and Srn CA and NV tonight and drop to around 5 to 15 degrees below normal for Srn OR and Nrn CA and near normal to 10 degrees below normal for most of NV and Central and Srn CA Sunday morning and below normal to around 15 degrees for most of the region Monday morning. Freezing levels generally near 2000 ft around ORCA border and around 4500ft near I-80 and around 6000 ft in the Srn Sierra and drop overnight to around 1500 ft near ORCA border and around 2500 ft near I-80 and around 4000 ft for Srn Sierra and 5000-7500 ft for Srn CA Saturday morning and fluctuate before rising to around 2500 ft near ORCA border and 3500 ft near I-80 and 5000 ft for Srn Sierra Sunday afternoon. .METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)... Forecast overall remains on track for additional precipitation across the region early to mid next week. Monday an upper trough will move into the PacNW bringing precipitation to northern/central CA and nrn NV. The trough will continue to move eastward through the PacNW on Tuesday allowing precip to continue across much of the region. Meanwhile an upper low will approach early next week just behind the trough. The GFS has been keeping the low offshore as it moves to the south while the 00z run of the ECMWF brought it inland. The new 12z det ECMWF also now keeps the low offshore the rest of the period. Either way, the continued presence of troughing over the PacNW/intermountain West should allow for periods of shower activity the rest of the long term. In spite of the ECMWF overall pattern becoming a bit closer to the GFS the large differences in QPF that were there this morning remain. The ECMWF is still much wetter than the GFS again forecasting 0.75-1+" around the Smith Basin 18z Mon- 00z Tues while the GFS is near a tenth of an inch. These discrepancies are present throughout much of Monday and Tuesday. Ensemble spread remains wide as well at over 2" at Arcata and similar divisions with the clusters as the 00z runs. QPF clusters for Monday (ending 12z Tues) are split in 3 with 77% of the GFS ensemble members in the drier (though less dry than earlier) first cluster while the ECMWF is divided (18%, 54%, 28%) between the three. It is a similar story for Tuesday as well. Actually precip amounts will depend on the depth of the PacNW trough, how quickly it moves through, and whether or not the low stays offshore. There are a variety of scenarios playing out in the ensembles, making for continued uncertainty in the QPF. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Osborne/AS $$