Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 830 AM PDT Wed May 1 2024 ...LIGHT PRECIP POSSIBLE OVER FAR NORTH TONIGHT INTO THURSDAY AND AGAIN ON MONDAY AS DISTURBANCES BRUSH BY TO THE NORTH... ...PRECIP POSSIBLE OVER SRN OR AND NRN CA FRIDAY AFTERNOON/NIGHT AND SPREADING SOUTH AND EAST SATURDAY WITH SHOWERS POSSIBLE SUNDAY MAINLY OVER THE SIERRA INTO NV... .METEOROLOGICAL CONDITIONS (WED AM - TUE AM)... Upper level ridge over the Central Eastern Pacific (centered around 145W) with a trough over the NW U.S. with disturbances moving through. A disturbance enters the Pac NW tonight and into the Great Basin Thursday brushing by the far north portion of the region for periods of light precip possible over the Srn OR Cascades and near ORCA border and Nrn NV tonight into Thursday. Moisture plume around 1.1 inches across the Eastern Pacific and along the Nrn CA coast on Thursday. Precip amounts expected to be generally up to a quarter of an inch except around half an inch to an inch along far NW CA coast and Srn OR Cascades and local amounts in higher terrain of Nrn NV. Freezing levels generally around around 7000 ft and higher this afternoon and dropping to around 5500-7000 ft over the far north tonight into Thursday morning. Weak ridging over the region Thursday night into early Friday in between systems as the trough over Nrn Great Basin shifts to the east and an upper level low pressure system approaches the NW Coast. This low pressure system is expected to drop down the west coast to off the Oregon/ Nrn CA coast Saturday afternoon and then inland Saturday night and into the Great Basin on Sunday. Moisture plume around 1.1 inches along the Nrn Ca coast Friday shifts south to around the Bay Area Saturday morning and around Point Conception Saturday afternoon/evening and weakens as it moves south along Srn CA Coast Saturday night into Sunday morning. Models are in a little better agreement (det GFS farther north than yesterday and EC a little farther south and timing a little quicker) than yesterday but still variability with the timing and track and strength for lower confidence in precip amounts and coverage and timing. The 24 hr QPF 50th percentile clusters ending 00Z Sunday show precip over Srn Or and Nrn CA but vary in amounts and extent with 2 clusters ( cluster 1 41 % of members and cluster 2 32% of members) showing precip down to around Monterey Bay Area and into Central Sierra with amounts 1.5 -3 inches along NW CA coast and 1-2 inches over Shasta and into Nrn Sierra and Cluster 3 27% of the ensemble members (canadian 30% and GFS 27% and EC 26%) keeping precip farther north along the Coast from around Pt Arena and north and over higher terrain of Nrn CA and into far Nrn NV and lower amounts. For 24 hr QPF 50th percentile clusters ending 00Z Monday around a quarter (23 %) of ensemble members have precip mainly confined over Nrn NV and the other ensemble members (around 77%) generally having precip along the Sierra and east over Nevada and near ORCA border. The forecast mainly uses a combination of the latest NBM and WPC with some of the previous forecast for Friday into the weekend. Precip may start as early as Friday afternoon over the NW CA coast and Srn OR Cascades and increase and spread south and east into Nrn NV and possibly Central CA Friday night into Saturday as the front moves through the region. Precip tapers off Saturday night into Sunday as the moisture plume and front shift out of the region and low moves through the Great Basin. Highest precip amounts around 1.5-2.5 inches expected over the NW CA coast and 1-2 inches over the Srn OR Cascades and Shasta Basin and into the Nrn and Central Sierra and Ruby Mtns. Freezing levels currently forecast to be around 7000 ft and higher Friday afternoon then drop to 3000-5000 ft over Nrn CA Saturday and around 5000-7000 ft over Central CA Saturday afternoon and 3000-5000 ft over Nrn and Central CA and 4000-6000ft over Nrn and Central NV Saturday night and rising to around 4000-6000 ft over Nrn CA and 6000-8000 ft over Central CA and NV on Sunday. Another disturbance moves into the Pac NW and brushes the far north portion of the region on Monday for a chance of light precip over the far north. Freezing levels generally around 7000 ft and higher on Monday except around 4000-6000ft for the far north. |