####018004270#### AGUS76 KRSA 081448 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 830 AM PDT Mon Apr 8 2024 ...WARMER AND DRY TODAY INTO EARLY THURSDAY WITH POSSIBLY THE WARMEST TEMPS SO FAR THIS YEAR ON WEDNESDAY AND THURSDAY... ...CHANCE OF PRECIP LATE THURSDAY INTO SATURDAY MAINLY OVER SRN OR AND NRN AND CENTRAL CA AND NV ALONG WITH COOLER TEMPS AS A LOW APPROACHES THE CA COAST... .METEOROLOGICAL CONDITIONS (SHORT TERM: MON AM - THU AM)... Low near the CA/AZ/NV border this morning drops southeast as high pressure builds into the region from the Eastern Pacific today. High pressure remains over the region into early Thursday bringing warmer and dry conditions. Max temps generally warm to near normal to 10 degrees below normal this afternoon and near normal to 10 degrees above normal Tuesday and 5 to 15 degrees above normal Wednesday with possibly the warmest temperatures we have seen so far this year. Overnight temperatures generally warm to near normal to 10 degrees above normal tonight and up to 15 degrees above normal Tuesday night and 5 to 15 degrees above normal Wednesday night. Freezing levels rise to around 7000 ft and higher over the region this afternoon and 9000-12000 ft Tuesday afternoon and remain around there Wednesday. .METEOROLOGICAL CONDITIONS (LONG TERM: THU AM - SUN AM)... Mostly dry conditions on Thursday as ridging passes over the west coast ahead of the next system. An upper low will then approach from the nw into Friday. The system is expected to stall offshore of the nrn CA coast before moving inland sometime over the weekend. There is a considerable amount of uncertainty with this system, particularly over the timing. The ensembles show arrival of precip anytime between Friday morning and Saturday evening. 24 hr QPF clusters ending 00z Sunday are split into 3 groupings at 54%, 26%, and 20%. Cluster 1 is entirely dry aside from some light showers over nrn NV and has at least half of the CMC membership, 68% of the ECMWF, and 30% of the GFS. Clusters 2 and 3 are progressively wetter suggesting earlier arrival times of the low. Models then differ on how long the system will stall offshore before moving inland as well as its relative position along the coast. The det ECMWF has the low a bit closer to the CA coast Saturday morning pushing more moderate precip inland sooner than the GFS. The ECMWF then slowly carries the low to the south along the coast past the Bay Area by early Sunday morning. The GFS parks the low west of Cape Mendocino just on the eastern side of 130W Saturday morning rotating in place most of the day before shifting a bit se overnight. On 12z Sunday, the GFS has the low west of Point Arena while the ECMWF has it west of the Monterey Bay. Bottom line, a return to wetter conditions is expected towards the end of the period as an upper low approaches CA. Uncertainty on the QPF due to model differences and ensemble spread. The official forecast was a blend of the morning WPC guidance and the latest NBM. Highest amounts expected along the central coast and across the Sierra. QPF 12z Fri-12z Sun: 0.50-1.25" Bay Area/central coast, 1-2" central coast mountains, 0.75-1.50" across the Sierra, 0.50-1" Shasta, 0.30-0.75" north coast/soCal coast, 0.25-0.80" down the valleys, and little to no precip over se CA and the far srn CA coast. Freezing levels Thursday morning starting at 9.5-12 kft across the region from n to s. The approaching low will lower levels from nw to se down to 7.5-9.5 kft north of I-80 and 9.5-11 kft to the south Fri afternoon. Levels will continue to lower into the weekend from west to east 3.5-5 kft from the coast to the foothills north of SLO county and 6-11 kft across the rest of the state. By the end of the period, expecting nrn/cntrl CA to be down to 4-6 kft and then 6.5- 10.5 kft for soCal and NV. Though, exact levels will depend on how long the low stalls offshore and its position when it does. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Osborne/AS $$