Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/22/20

Area Forecast Discussion
National Weather Service San Francisco Bay Area
416 PM PST Fri Feb 21 2020 .SYNOPSIS...A slight chance of light rain showers for the Central Coast into Saturday morning as a system to our south impacts southern California. High pressure redevelops by early next week bringing a continued dry and warm conditions regionwide. && of 03:00 PM PST Friday... An atypical weather pattern for late winter is in place over the region this afternoon. A 555dm 500mb upper low is positioned approximately 425 miles SSW of San Francisco while a low amplitude, progressively tilted high pressure ridge is beginning to build into the state from the northwest. Moist S/SW flow on the E/NE flank of the upper low has continued to advect in mid to mainly upper level moisture over the southern counties (Monterey, San Benito, Santa Cruz, and southern Santa Clara). KMUX radar has showed increasing reflectivity signatures off the Big Sur coast and eastward into the Central Valley in an area of elevated diffluence on the NE periphery of the upper low. So far, we have not received any reports of any precipitation making it to the ground and instead have mainly had eye witness reports of virga (ie rain falling but evaporating before it makes it to the surface) -- which is not too surprising with these higher based showers. Forecast models have steadily backed off on coverage, probability and amounts of any precipitation expected in the southern counties over the last 12 to 24 hours, with the latest Euro ensemble showing mostly dry members even as far south as Big Sur station. Latest HRRR hourly output keeps the area mostly dry as well, with some weaker wrap around showers arriving late tonight into Saturday morning mainly over southern Monterey and southern San Benito counties. Otherwise, temperatures are running much warmer than the same time yesterday in response to warm air advection (+1-2C/prev 24hr at 850mb) aloft. At the surface, this has translated to temperatures running roughly 3-7 degrees over yesterday`s readings, which puts the area at around 6-14 degrees above seasonal normals for today. As of 2pm, Santa Rosa was 74F, which is +10F over 64F yesterday, and Monterey was 73F which is +8F over 65F yesterday. Intermittent cloud coverage has resulted in a mixed bag in day over day temperature changes however with a few pockets under thicker cloud cover near or even cooler than this time yesterday. Temperatures are forecast to relax by 5-10F regionwide this weekend as low pressure passes to the north and onshore flow picks back up. Dry conditions persist next week as well. A broader, higher amplitude high pressure system will then develop early next week, pushing 850mb temperatures up to 12-15C from Tuesday through Thursday -- resulting in further dry, unseasonably warm weather for the region. Some inland areas could approach or surpass 80F on Wednesday or Thursday of next given recent model trends. This dry weather opens the door for many areas to receive no precipitation for the month of February, including downtown San Francisco. In all the years that weather observations have been taken in downtown San Francisco, this has only occurred once before -- in 1864. && of 4:15 PM PST Friday...Upper level low dropping south off the coast into the southern California offshore waters. This will bring a chance of showers to the MRY Bay Area and possibly as far north as SJC but cloud bases will remain in the VFR range. Vicinity of KSFO...VFR with mid to high cloudiness. Winds remaining under 10 kt. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...VFR. A chance for showers between 07Z and 15Z with clouds bases getting as low as 5000 ft. && of 04:02 PM PST Friday...An upper level low will move to near Point Conception by early Saturday morning then quickly move eastward during the weekend. The low will bring a chance of showers over the southern coastal waters late tonight and Saturday. A strong high pressure system will build over the eastern Pacific late in the weekend and next week. Northwest winds will increase over the northern waters by early tonight and increase to the south on Saturday. Expect moderate period northwest swell through early next week. A long period northwest swell is likely mid next week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 10 PM && $$ PUBLIC FORECAST: DRP AVIATION: W Pi MARINE: Sims Visit us at Follow us on Facebook, Twitter, and YouTube at: