756 FXUS66 KSGX 281651 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 950 AM PDT Thu Mar 28 2024 .SYNOPSIS... A Pacific storm moving down the coast will strengthen the onshore flow today and Friday bringing gusty west winds to the mountains and deserts. The storm will then bring widespread rain and mountain snow to Southern California Saturday and Sunday. Steady precipitation Saturday will transition to showers and isolated thunderstorms Saturday night and Sunday. Lingering showers Monday will be followed by dry and warmer weather Tuesday and Wednesday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The infrared satellite loop this morning showed the circulation center of the deep 530 dm closed low west of the state of Washington. A strong shortwave diving south out of the Gulf of Alaska tonight will deepen a longwave trough down the West Coast and spin up a 535 dm west of SFO Friday evening. Surface pressure falling over the Great Basin this afternoon will result is strong onshore gradients that will bring blustery westerly winds to the mountains and deserts this afternoon through Friday. Blowing dust and sand will impact some deserts areas. The upper low digs south toward Pt Conception Saturday, tapping into a moisture plume over the Pacific that will make landfall over the Southwest Friday night and Saturday. Moderate to heavy rain over Santa Barbara Friday evening will move south across the LA basin Friday night, and then spread south into Orange, San Bernardino, Riverside and San Diego Counties Saturday morning. This is when steady moderate to heavy rain is likely. The combined effects of the PVA aloft, the lifting along and ahead of the surface cold front and the orographics over the mountains will produce rainfall rates of 0.50" or more. After the AR passes Saturday afternoon, the cold core low behind the trough will settle over the Southwest, and a second trailing vort max which will help fuel showers and a thunderstorms in the unstable airmass Sunday. Showers will linger into Monday in the broad cyclonic flow trailing the upper low which will dig all the way to central Baja Monday evening. Ridging slowly builds over the Southwest Tuesday through Thursday for warmer days. && .HYDROLOGY... Rain and mountain snow will begin as early as Friday night in Orange County and the San Bernardino Mountains, then move south across the Riverside and San Diego Counties Saturday morning. On Saturday night and Sunday, showers will be fairly widespread with locally heavy rain rates in any thunderstorms that form in the cold unstable airmass behind the trough. Forecast Rain Totals Through Monday: Coastal and Valley........1.00"-2.00" Mountains.................2.00"-3.50" locally 5.00" in the SBD mtns Highs Deserts.............0.50"-1.00" Lower Deserts.............0.25"-0.50" The snow level between 5500-6000 feet Saturday morning will fall to 4500 feet Saturday night, then fluctuate around 5000 feet on Sunday. Projected Snow Totals Through Monday: 4500-5500 ft...0-3" 5500-6500 ft...3-6" 6500-7500 ft...6-12" Above 7500 ft..12+" The current forecast for the San Diego River at Fashion Valley has the river rising on Saturday, but remaining below the low-water crossings. With additional rainfall on Sunday, the river could rise sufficiently to flood the low-water crossings late Sunday. && .AVIATION... 280930Z...Coast/Valleys... Low clouds will continue through the morning hours at some of coastal sites. Bases will be 1000-1400 feet MSL with tops to 2000 feet. Vis reduced 0-5SM in BR along inland extent of clouds and higher coastal terrain. Scatter out 16-19Z. Low clouds will push ashore and inland after 01Z in San Diego County and after 06Z in Orange County. Bases will be around 1500 feet MSL but will rise to over 2000 feet MSL and fill most of the coastal basin overnight into Friday. Partial and intermittent cigs near the coast. Mountains/Deserts...Increasing westerly winds after 23Z with gusts of 25-35 kt, locally up to 55 kt. MOD up/downdrafts and turbulence expected over and east of the mountains. Surface winds should decrease after 09Z. Otherwise...occasional high clouds above 20000 feet MSL today and tonight. && .MARINE... No hazardous marine conditions are expected through Friday. Strong southerly winds and choppy conditions are expected Friday night and Saturday morning. A distinct wind shift from south to west will occur with a front moving through the coastal waters Saturday morning, with weaker winds and less chop thereafter. There is a slight chance of thunderstorms Saturday night through Sunday. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC/HYDROLOGY...Moede AVIATION/MARINE...Suk |