Hydrometeorological Discussion National Weather Service / California Nevada RFC / Sacramento CA 735 AM PDT Sat Apr 13 2024 ...COOLER AND UNSETTLED CONDITIONS THIS WEEKEND... ...DRYING THROUGH NEXT WEEK WITH TEMPERATURES REBOUNDING... .METEOROLOGICAL CONDITIONS (SAT AM - FRI AM)... This weekend will see the most impactful conditions in terms of precip as an area of low pressure is spinning west of the SF Bay Area generally along 125.5W this morning. The line of precip associated with the frontal boundary is currently arching from near Cape Mendocino back across the northern CA coastal mountains and then through the SF Bay Area and down to the central CA coast. Since 13/12Z...precip gauges show the best totals ranging from 0.10- to 0.25-inch with some localized higher amounts. Favorable upslope flow is occurring along the west side of the Sacramento Valley and adjacent coastal mountains as southeast low- to mid-level flow exists in the northeast quadrant to the area of low pressure. Models are in reasonable agreement with the progression of the system today with primary circulation slowly dropping toward the southeast before eventually moving inland somewhere along the Monterey county coast Sunday morning. The line of precip will shift inland and southward this afternoon with the best amounts focused from the American River basin down to the upper portions of the San Joaquin River basin and across areas near Point Conception...which include the Santa Ynez Mountains where a brief period of southerly flow exists ahead of the frontal boundary. Also...a mid-level vort max will rotate through the cyclonic flow...which will enhance precip across this area. By the evening and overnight...precip will focus over areas in the vicinity of the primary circulation near the SF Bay Area and central CA coast...the southern Sierra along with the San Gabriel and San Bernardino mountains where the frontal boundary will be traversing...and then near the CA/OR border in an area of convergent flow. Sunday will see the area of low pressure track inland toward southern NV with precip tapering off as the new work week starts. A couple disturbances moving through the cyclonic flow will bring the best precip to areas near Point Conception and far southern Sierra with the other being in the vicinity of the CA/OR border. Overall totals from this morning through Monday morning 12Z...the next 48 hours...will generally be from 0.75- to 1.50-inch with a few localized areas closer to 2.00-inches across the higher terrain from areas near the CA/OR border down to the transverse ranges of southern CA. Central Valley locations may be slightly less...with approx 0.33- to 0.75-inch with some areas on the east side of the San Joaquin Valley approaching 1.00-inch. Freezing levels are starting today with an tight east-to-west gradient...from 9000- to 11500-feet across much of NV and southern CA...while the cooler airmass near the area of low pressure is down to 3500- to 5500-feet across coastal northern CA down through the SF Bay Area and Monterey Bay area. As the area of low pressure moves inland later today into early Sunday...these will bottom out with 3500- to 5500-feet across much of northern and central CA and then eventually 5500- to 7000-feet for NV down toward southern CA. After this system moves downstream of the area on Monday...dry conditions are expected to set up shop for the rest of the week as modest high pressure builds over the area...and temperatures warm back to or just above normal. |