####018004268#### AGUS76 KRSA 082013 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 130 PM PDT Mon Apr 8 2024 ...WARMER AND DRY TODAY INTO THURSDAY WITH POSSIBLY THE WARMEST TEMPS SO FAR THIS YEAR ON WEDNESDAY AND THURSDAY... ...CHANCE OF PRECIP FRIDAY INTO SATURDAY ALONG WITH COOLER TEMPS AS A LOW APPROACHES THE CA COAST... .METEOROLOGICAL CONDITIONS (SHORT TERM: MON PM - THU AM)... No change to the dry and warmer forecast into mid-week. Low near the CA/AZ/NV border drops southeast into tonight as high pressure builds into the region from the Eastern Pacific. 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)... Forecast overall remains on track for a large upper low to impact CA late this week and into the coming weekend. The same sources of uncertainty persist regarding the arrival time of initial precip and the subsequent movement/positioning of the low. The GFS remains the slowest of the three between the GFS, ECMWF, and CMC in addition to keeping the low further to the north when it arrives offshore. The ECMWF is the quickest and furthest south taking the low inland around the Monterey Bay area overnight Saturday while the core of the low in the GFS is still just southwest of Cape Mendocino. The CMC is somewhere in between timing wise but is closer in n/s positioning to the GFS. This results in different arrival times for precip along the coast between the three and different QPF for various areas around CA. Ensemble spread on the timing and location of the low is just as wide as it was this morning showing precip reaching the coast anywhere from Friday morning to Saturday evening. 24 hr QPF out of the GFS/ECMWF ending late Saturday night at KMRY (Monterey Airport) is anywhere from 0 to nearly 2". The 12z model runs for the most part are not too different than the 00z/06z runs, though the 12z GFS has slowed down the precip compared to this morning only widening the gap between it and the ECMWF. To summarize, a large upper low is progged to bring precip to CA in the extended but there is a good amount of uncertainty on the details and amounts. The afternoon update was a blend of updated WPC guidance and the 12z GFS/ECMWF. This led to relatively minor changes on the order of 0.10- 0.25" along the coast and across the Sierra with 0.25-0.50" increase over Shasta. Highest amounts expected along the central coast and across the Sierra. QPF 12z Fri-12z Sun: 0.50-1.25" Bay Area/central coast/Sierra, 1-2" central coast mountains, 0.75-1.50" 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 4.5-7.5 kft from the coast to the foothills north of SLO county and 8-11 kft across the rest of the state Saturday afternoon. By the end of the period, expecting nrn/cntrl CA to be down to 4.5- 6.5 kft and then 6.5-11 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 $$