####018004331#### AGUS76 KRSA 022033 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 130 PM PDT Tue Apr 2 2024 ...DRY AND WARM WEATHER COMING TO AN END... ...COOLER AND UNSETTLED PATTERN FOR THE REMAINDER OF THE WEEK... .METEOROLOGICAL CONDITIONS (SHORT TERM: TUE PM - FRI AM)... No change in thinking as the pattern will evolve from a dry and warm regime to a cooler and unsettled one for the latter half of the week. Upr ridging across the area today will get displaced downstream tomorrow as a polar system over the Gulf of Alaska dives down the west coast and carves out a broad area of cyclonic flow across the region. Still expecting the potential for scattered precip this evening and overnight above Shasta Dam...ahead of the system that will eventually bring widespread precip to portions of the upper Klamath River basin and northeast CA on Wednesday in an area of diffluence aloft. Upslope flow will also generate widespread precip over the northern/central Sierra down to about the Merced River basin. Then into Thursday...the core of the system will move across central CA for the best precip between the Santa Cruz mountains down to the Big Sur coast and then inland over the southern Sierra from about the Tuolumne River basin to the Kings River basin. A band of precip is also expected to develop on the downstream side of the system from north-central NV back across the state toward west-central NV. Cool air will accompany this system with freezing levels peaking today from 10000- to 12500-feet...and plummeting in the cooler airmass...down to about 2000- to 5000-feet from northwest to southeast early on Friday. .METEOROLOGICAL CONDITIONS (LONG TERM: FRI AM - MON AM)... No major changes to the afternoon forecast with the largest change to decrease amounts up to a few hundredths over Srn CA on Friday morning. Upper trough/closed low over the region on Friday with the low center near the intersection of NV/OR/ID then shifting east Friday night as another system approaches the Pac NW coast. Showers possible over the region Friday especially over Srn Ca and over NV and along the Sierra. Precip amounts generally around 0.1-0.5 over Srn Ca with 0.25-0.75 with local amounts around an inch in the San Gabriel Mtns and into San Bernardino Mtns and South into San Diego County Mtns and around 0.25-0.5 inches over Srn Sierra and around 0.1-0.4 with local amounts up to .75 inches over Nevada on Friday. Max temperatures around 5 to 20 degrees below normal on Friday with the coldest temps over Srn CA and NV. Record low maximum temperatures are possible over Srn CA on Friday. Precip tapers off Saturday morning with weak ridging between systems. The trough off the Pac NW deepens over Nrn CA with a closed low forming by Sunday afternoon and moving South through CA. Showers, mainly along the coast and higher terrain, spread south and east across the region Sunday into Sunday night. There are still differences in the models and ensemble members in the details including the timing and track of these systems. Forecast mainly used a mix of latest WPC with NBM and previous forecast. Precip amounts generally around a tenth of an inch or less over Srn OR and Nrn CA and NE NV with local amounts up to a third of an inch over the Smith Basin and Ruby Mtns on Saturday. Precip amounts to around a tenth of an inch over Nrn and Central CA and portions of NV on Sunday with a few hundredths into Srn CA Sunday night. Temps warm a little over the weekend with max temps generally near normal to around 15 degrees below normal. Freezing levels around 2000-4000 ft (NW-SE) over CA and around 3000- 6000 ft (W-E) over NV Friday morning then rising to 3000-4500ft over CA and around 4000-5500ft over NV in the afternoon and around 2500- 4500ft over the region overnight then around 3000-5000 ft over Nrn and Central CA and 4000-7000 (N-S) over NV and around 6000-8000+ over Srn CA Saturday then dropping to around 4000-6000 ft over Srn Ca and NV Sunday night. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Kozlowski/Osborne $$