AGUS76 KRSA 171525 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 730 AM PST Mon Feb 17 2025 ...SHOWERS OVER SRN OR AND NRN CA/NV TODAY AS A TROUGH MOVES THROUGH... ...NEXT SYSTEM TO BRING MORE WIDESPREAD PRECIP TO NRN CA/NV AND SRN OR ON WEDS WITH ADDITIONAL SHOWERS POSSIBLE OVER THE NORTH COAST INTO SUNDAY... .METEOROLOGICAL CONDITIONS (MON AM - SUN AM)... A trough continues to dig into the PacNW and ne CA/nrn NV this morning as a ridge follows behind it over the eastern Pacific. The result is some light returns on the radar over srn OR and along the north coast. Observations overnight reporting generally 0.10-0.50" with locally higher amounts and a few hundredths to a tenth of an inch inland across nrn CA. Showers will persist over srn OR, nrn CA, and nrn NV the rest of today as the trough continues to move southeastward through the region. Conditions will dry out from west to east into the late afternoon/evening as the ridge moves in behind the trough. The ridge will pass through the west coast on Tuesday keeping the region dry as the next system approaches for mid-week. Models continue to change the structure of the trough that is going to be moving through on Wednesday as well as the general timing. Today's runs have slowed things down a bit and shortened the length of the overall system. Earlier runs had a much longer skinnier trough while today is showing the shallower system forming off into a closed low offshore of srn OR by early Wednesday morning. They also keep precip away from the coast overnight Tuesday leading to a decrease in the QPF for today's forecast for that time period. Wednesday morning the core of the low will head inland near the OR/WA border as the trough moves through nrn CA and into NV in the afternoon spreading precip as it does so. Time period for heaviest precip will be 12z Weds to 00z Thurs with the highest amounts focused along the north coast. The system will then continue to slowly move through into Thursday with a ridge building in behind it drying conditions out throughout the morning. Only lingering showers over NV in the afternoon/overnight as the trough begins to exit into the Four Corners. Ensembles in relatively good agreement on precip coverage with some disagreement on amounts along the north coast. QPF for the short term a combination of showers from today's trough and the Wednesday system, majority of this will be Wednesday. QPF 12z Mon-12z Thurs: 1-2" north coast (2-3.25" Smith Basin), 1-2.25" srn OR Cascades, 0.25-0.75" nrn CA inland to Shasta, 0.10-0.50" south of Shasta/Mendocino, and a few hundredths to 0.25" around the Bay Area and down the valley. For Thursday looking at generally 0.10" or less of lingering showers over ne NV and over srn OR. High pressure will remain overhead on Friday and Saturday keeping the region dry. Models then have another system moving across the Gulf of Alaska towards BC and the PacNW. Some uncertainty as to how far south precip will spread from this late Saturday into Sunday. Det models have very little to no precip south of the OR border as high pressure steers everything to our north. About a third of the ensemble members (45% CMC, 3% GFS, 42% ECMWF) have no precip reaching the Smith Basin through Sunday afternoon while the rest show at least something along the north coast (0.50-1.50" cluster 1, 0.10-0.75" cluster 2). The official forecast blended WPC with the NBM but trimmed back the extent of precip the NBM was showing. QPF for Saturday about 0.10-0.25" for the north coast and up to 0.50" over the Smith Basin tapering off to zero by Shasta. Freezing levels Monday mid morning 4-7.5 kft north of I-80 and 6.5- 10 kft I-80 to the southern Sierra. Lower levels will then spread eastward the rest of Monday reaching 4.5-9 kft across the Sierra and 4.5-6.5 kft for most of NV early Tuesday. Higher freezing levels will return from sw to ne the rest of the day to 7-9.5 kft north I- 80 overnight before lowering again Wednesday with the next trough. Freezing levels Wednesday afternoon across the Sierra 4.5-9.5 kft rising back up again to 7-10.5 kft by Thursday afternoon. Another increase into Friday up to 8.5-11.5 kft across most of the region. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php AS $$