####018004314#### AGUS76 KRSA 232103 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 105 PM PST Fri Feb 23 2024 ...DRY THROUGH THE WEEKEND... ...CHANCES OF PRECIP RETURNING NEXT WEEK... .METEOROLOGICAL CONDITIONS (SHORT TERM: FRI PM - MON AM)... Dry conditions will continue into the weekend as the offshore vertically stacked system remains outside of 130W...and the disturbance dropping southeast toward the Pacific Northwest will reach the coast early Monday. As both these systems near the region...scattered light precip will develop over coastal northern/central CA...and then inland over the crest of the southern OR Cascades down across much of the Sierra. Totals through Monday morning will be 0.10-inch or less...except near Crater Lake where amounts may approach 0.25-inch. Freezing levels will generally be near 6000-feet at the CA/OR border...7000-feet along I-80...and approaching 8000-feet for central CA. .METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)... Forecast continues to trend in a drier direction this afternoon as QPF has gone down another 0.10-0.25" or so for the extended. A surface/upper low is still expected to approach CA on Monday while a trough digs into the PacNW. Deterministic models show again in the 12z runs relatively minimal interaction between these systems as the PacNW trough is not forecast to dip very far into the region while the low is still offshore. The low will bring some showers to central/southern CA on Monday into Tuesday while the trough brings showers to northern CA/NV. Biggest areas of uncertainty for the Monday systems are how far south the trough will dig into northern CA/NV and therefore how far south it will spread precip. The other is on how much precip will fall over the Sierra. 24 hr QPF spread over the Sierra still ranges from 0-0.25" to 0.75-2+". Roughly half of the ensemble members between the GFS/ECMWF/CMC in total are grouped into QPF cluster 1 and are on the drier side. The other 48% show widespread totals of over an inch. The GFS and CMC members are generally on the wetter side compared to the ECMWF. For the official forecast went with WPC guidance which leans on the wetter side (though not as wet as the CMC/GFS ensembles). The trough will exit the area later Tuesday as the offshore low shifts south and approaches Baja moving through into Wednesday. Most of the area should remain dry for Tuesday aside from light showers possible across far nw CA thanks to a weak system moving into the PacNW. A larger system will then move into the Gulf of Alaska later Wednesday sending a surface low and front towards the PacNW. The southern edge of the front is forecast to shift enough to the south to bring precip to the north coast late Weds into Thurs. Still some uncertainty on how far south exactly it will shift. QPF clusters ending 12z Thurs are split into 3 groups at 42%, 31%, and 27%. The first is the wettest showing 0.50-2" along the north coast. Cluster 2 is essentially dry keeping nearly all the precip north of the OR border while cluster 3 is somewhere in between. The official forecast went with the latest run of the NBM, which spreads precip just south of Cape Mendocino ranging from 0.30-1.50". For days 4-6 the highest precip amounts are expected near the Smith Basin/srn OR Cascades and along the Sierra. QPF for 12z Mon-12z Thurs: 0.50-2" north coast (highest Smith Basin), 1-2" srn OR Cascades, 0.60-1.25" Sierra, 0.25-0.50" central/srn CA coast, 0.25- 0.50" Shasta, generally a few hundredths to 0.25" for the rest of CA, and 0.30-1" over the NV mntns. Freezing levels Monday morning, expecting 3.5-7 kft north of I-80 and 6.5-10.5 kft to the south. Levels reach a min Tues am at 2.5-7 kft north of I-80 and 6.5-9 kft to the south before increasing again. Freezing levels then hit 4.5-7.5 kft north of I-80 and 7-8.5 kft to the south Weds am before rising a bit later in the day to 5- 7.5 kft north of I-80 and 7-9.5 kft to the south by Thurs am. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php Kozlowski/AS $$