Subj : MESO: CA Heavy Rain/Flood To : All From : Mike Powell Date : Mon Feb 19 2024 08:33:00 AWUS01 KWNH 190847 FFGMPD CAZ000-191830- Mesoscale Precipitation Discussion 0065 NWS Weather Prediction Center College Park MD 345 AM EST Mon Feb 19 2024 Areas affected...Much of Central and Northern CA Concerning...Heavy rainfall...Flash flooding possible Valid 190845Z - 191830Z SUMMARY...A threat of heavy rainfall will continue for the remainder of the night and into the morning hours as a strong low center persists offshore of the West Coast. This will maintain a threat of flooding given the locally saturated ground conditions. DISCUSSION...A deep low center offshore of the West Coast associated with an upper-level trough will continue to advance gradually off to the east over the next 6 to 12 hours which will allow a cold front to advance inland across central and northern CA. A rather well-defined atmospheric river of Pacific moisture continues to advance north around the eastern flank of the deep layer trough/low and this will maintain a threat of heavy rainfall going through the remainder of the night and into the morning hours for much of the region. The axis of strongest warm air advection/isentropic ascent and deep layer moisture transport will be across the San Joaquin and Sacramento Valleys as well the west-facing slopes of the Sierra Nevada. Locally enhanced low-level jet energy of 40 to 50+ kts continues to lift northward up through the Central Valley, and the latest RAP analysis continues to show a modest axis of instability with MUCAPE values of as much as 100 to 250 J/kg. This coupled with some locally strong low-level moisture convergence over the Central Valley and near the foothills of the Sierra Nevada continue to support some occasionally stronger convective elements with heavier rainfall rates. Rainfall rates within the main warm conveyor belt along and ahead of the cold front will have the capability to occasionally reach into the 0.50" to 0.75"/hour range with some spotty heavier rates possible where any stronger convective cells materialize. Behind the cold front, there should tend to be a break in the coverage of moderate to heavy rainfall, but eventually there will be the arrival of additional shortwave energy from offshore along with the arrival of steeper mid-level lapse rates. This coupled with orographics is likely to result in some redeveloping yet broken lines of showers and thunderstorms. The 00Z HREF and especially the HRRR tend to favor the Bay Area, northern CA coastal ranges, and the northern Sacramento Valley as having the best potential of seeing these semi-organized bands of convection this morning. Along and ahead of the cold front, additional rainfall totals of as much as 2 to 4 inches with isolated heavier amounts can be expected for the upslope areas of the Sierra Nevada below the snow line, with eastern portions of the Central Valley seeing as much as 1 to 2 inches. The areas that do see more discrete convection redeveloping early this morning closer back to the Bay Area and up north across the coastal terrain and northern Sacramento Valley may also see some additional 1 to 2 inch amounts. Given the heavy rainfall that has already occurred, and with locally saturated ground conditions, these additional rains should maintain a flooding threat going into the morning hours. Orrison ATTN...WFO...EKA...HNX...MFR...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41252339 41012207 39862093 38451992 38271982 37531929 37111884 36621857 36161873 35791923 35801978 36182012 36682048 36972100 36922139 36822173 36922208 37242251 38202304 38632349 39262391 39832397 40372439 40982413 = = = --- SBBSecho 3.14-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/105) .