####018004258#### AGUS76 KRSA 111425 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 725 AM PDT Thu Apr 11 2024 ...WARM CONDITIONS COMING TO AN END AS HIGH PRESSURE MOVES EAST... ...LOW PRESSURE FROM THE NORTHWEST IMPACTS THE REGION THIS WEEKEND... .METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - SUN AM)... The overall pattern shows the upr ridge shifting inland across the western US this morning...while upstream a deep upr low over the Gulf of Alaska has started to drop south-southeast and will parallel the west coast until it reaches down toward CA this weekend. For today...the above normal temperatures will be the highlight with mainly dry conditions. Anomalies are looking to be generally from plus 5- to plus 15-degF over seasonal norms. Models continue to hint at the possibility of rather scattered precip developing near the crest of the southern Sierra and near the Shasta Lake drainage. By Friday morning...the upr low will reach a location just above 30N and just outside of 130W. The 11/00Z deterministic models show less of a spread with the location of the primary circulation around 132.5W. Ahead of the upr low...the frontal boundary will entrain moisture with peak PW values just above 0.75-inch poised just off the northern CA coast. Throughout tomorrow...the system will then wobble toward the southeast and settle just west of the SF Bay Area by early Saturday. Models are in better agreement with the best precip remaining along coastal areas of northern and central CA (0.25- to 0.50-inch) through 13/12Z with less of an impact inland across the Shasta Lake drainage down the northern/central Sierra (0.10- to 0.33-inch). Saturday looks to be the day with the greatest impact across CA as widespread precip is expected and to a lesser degree over NV. The upr low will slowly make its way toward the coast with individual disturbances rotating around the primary circulation. Widespread amounts in the range of 0.50- to 1.00-inch are expected with totals approaching 1.50-inches for the Big Sur coast...the Santa Ynez range of Santa Barbara and Ventura counties...and the southern Sierra between the Tuolumne River basin and the upper San Joaquin River basin. Freezing levels today are at their peak with the upr ridge moving inland and then downstream of the area...from 9500- to 12500-feet from north-to-south. Then as the core of the upr low moves across the SF Bay Area on Saturday...the coolest air will move overhead with these bottoming out around 3500- to 5000-feet across northern and central CA with slightly higher for southern CA and much of NV (5000- to 8000-feet) by early Sunday morning. .METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)... Guidance continues to show uncertainty on the exact details of the upper low as it pinwheels off the central/southern California Coast on Sunday. The exact location and amounts of precipitation across the region remain in question. The GFS continues to suggest stronger southerly onshore moisture flux into the western Transverse range, leading to nearly 0.75 inches over Ventura County on Sunday, compared to 0.25 inches in the EC. A slightly more northward trajectory of the low inland from the EC places slightly more precipitation over northern California compared to the GFS. Morning forecasts mainly followed the NBM and WPC with up to 0.25 inches over southern California and <0.10 inches across the higher elevations of central and northern California on Sunday. A majority of guidance has the low moving inland on Monday, with minimal shower activity. Ridging will begin to dominate next week, leading to warmer and drier conditions across the region. Freezing levels are forecast to begin the period below 4,000 feet over northern California and above 5,000 feet over southern California/Nevada before rising under the building ridge to above 4,000 feet across the north and 12,000 feet across the south. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Kozlowski/CH $$