####018003809#### AGUS76 KRSA 292050 HMDRSA Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 1250 PM PST Thu Feb 29 2024 ...LARGE SLOW MOVING SYSTEM TO BRING WIDESPREAD PRECIP AND MOUNTAIN SNOW TO THE REGION THROUGH THE WEEKEND... ...ADDITIONAL PRECIP CHANCES NEXT WEEK... .METEOROLOGICAL CONDITIONS (SHORT TERM: THU PM - SUN AM)... Satellite and surface analysis shows the cold front moving through nw CA as the surface/upper low remain over the Gulf of Alaska. Radar imagery recording precipitation across northern CA with some upslope rain/snow over the northern Sierra. Can also see a convective line moving across I-5 with multiple lightning strikes/flashes. Another 0.50-1+" has fallen the past 6 hours with the highest amounts along the north coast and through to Shasta. Forecast remains on track for the front to continue to slowly traverse the region the next 24 hours or so with another front on its heels set to arrive Friday afternoon along the north coast. Meanwhile the low will continue its southerly crawl offshore before shifting into an eastward direction Friday afternoon/evening and through the rest of the short term. Cold air behind the front and with the core of the system will allow for thunderstorm chances for parts of nrn CA through at least Saturday. HREF exceedance probabilities are about 20-60% for 0.50"/hr rainfall rates through this evening for parts of nrn/cntrl CA. Little has changed in terms of the ensemble distribution in the 12z runs. The ECMWF continues to place all its eggs in one cluster for the next 24 hrs, but this time is joined by about half the GFS members. There have not been any big changes in the 12z model runs compared to yesterday. The afternoon forecast was a blend of WPC guidance, the latest NBM, and the previous forecast. This amounted to about a 0.10-0.25" change for most areas and another increase of 0.25-1" across the Sierra. Precip totals 18z Thurs to 12z Sun: 1.75- 3.50" CA coast Sonoma northward (4-6.50" around the Smith Basin), 3.50-10+" Sierra, 2-5.50" Shasta, 2-4" central coast mountains, 0.75- 2" Bay Area/central coast, 0.35-1.75" down the valleys (closer to 2" towards the foothills), 0.30-1+" coastal soCal LA County to Point Conception (1-2" mountains), and 0.10-0.25" the rest of the srn CA coast. Freezing levels to lower behind the cold front today down to 2.5-5.5 kft north of I-80 this afternoon and 5.5-8.5 kft to the south to Point Conception. Some fluctuation the rest of the week but overall trending downward reaching a minimum Saturday morning of 1.5-2.5 kft north of I-80 and 2.5-5.5 kft to the south to Point Conception and staying roughly at those levels the rest of the short term. .METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)... Guidance continues to suggest the departure of the broad upper-level trough out of the forecast region on Sunday, leading to a tapering off of precipitation throughout the day and into early next week. Shower activity is forecast to linger across northern California as multiple pockets of positive vorticity advect across the region though accumulations will be relatively light. Due to the nature of these vorticity pockets, exact timing and location of shower activity is in question. Maximum temperatures will likely remain below normal throughout the extended range forecast Afternoon forecasts continued to follow guidance from the NBM and WPC slightly decreasing accumulations across the North Coast, Shasta Basin, and northern Sierra. QPF graphics are available at www.cnrfc.noaa.gov/qpf.php AS/Osborne $$