828 FXUS66 KSGX 240411 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 910 PM PDT Fri Aug 23 2019 .SYNOPSIS... High pressure is building over the State, and will thin the marine layer and limit nocturnal low cloud development. It will also boost daytime temperatures. Expect very warm to hot conditions inland, with some warming over coastal areas as well, especially prior to sea breeze onset. Some moisture will move in from the east, but no showers or thunderstorms are expected. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... At 9 PM PDT...Satellite imagery showed patchy high clouds drifting to the SW over SoCal, with all the low marine clouds well offshore. Monsoonal thunderstorms were occurring over SE AZ and Sonora MX. The 00Z Miramar sounding still indicated a fairly deep marine layer near 2K FT, topped by a 5C inversion. Winds through the mid-levels were SE 10-15 KT. Weak to moderate sfc pressure gradients continued from the coast to the deserts with peak W-SW wind gusts of 20-30 MPH. It looks like there is at least a potential to exceed forecast max temps on Saturday over inland coastal and western valley areas, depending on the onset of the sea breeze. Not enough confidence to make forecast changes this evening though. From previous discussion... Our coastal eddy keeps on cranking, but low clouds cleared out fully and nicely this morning. The eddy will gradually fade tonight. Low clouds will move ashore and inland overnight, but probably not as far as they got this morning. A gulf surge is probable in the lower desert again Saturday morning, a sort of desert style marine layer. They should get some low clouds out there, but not full overcast. A trough of low pressure moving through the interior West today will quickly lift out and allow a nose of high pressure from the Pacific to build into California. That will take care of the eddy. This banana-shaped ridge extends from San Francisco to Phoenix on Sunday and Monday. That will tamp down our marine layer so that clouds only cover the coastal areas nights and mornings. It will also bring us a modest warming trend through about Tuesday. The ridge weakens slightly to back off temps a couple degrees around the middle of next week. Some increase in monsoon moisture at mid levels of the atmosphere is happening this weekend, but with little if any instability. That means we'll see some cumulus clouds over the mountains during the afternoons, and nothing more. That moisture retreats for a few days, then models depict a return later next week. Maybe the following weekend we get a chance of thunderstorms. Or not. That's what we've been saying for the last couple weeks when we were thinking we might get thunderstorms today. Needless to say, confidence is really low. The monsoon season is quietly slipping by without too many thunderstorm days; our next tstorm might not arrive until September. What impact will Ivo have on SoCal? None in the weather department, but we do expect him to bump up in the swell and surf (see Beaches discussion below). The high pressure could build a little stronger over SoCal toward next weekend, which would bring us another modest warming trend. && .AVIATION... 240400Z...Coast/Valleys...Stratus will be much less widespread tonight, with areas of BKN-OVC cigs developing within 10 miles of the coast 06Z-10Z Sat. Bases will be 1200-1500 ft MSL with tops to 1700 ft MSL. Most vis will remain 5+ miles. Most areas will clear 15Z-17Z Sat, with VFR conditions prevailing after 17Z Sat, likely continuing Sat evening. Mountains/Deserts...Mostly clear with unrestricted visibility through Saturday evening. && .MARINE... No hazardous marine conditions are expected through Wednesday. && .BEACHES... South-southeast swells from 160-170 degrees with a 12-14 sec period generated by Tropical Storm Ivo will reach the beaches of southern California late Saturday, peaking Sunday before lowering Monday and Tuesday. These swells could produce isolated surf up to 6 ft and strong rip currents on the more southerly-facing beaches of Orange County. West facing beaches, mainly in San Diego County, will have little or no effects. A Beach Hazards Statement is in effect for Orange and San Diego county beaches Saturday night through Tuesday morning with biggest impacts being strong rip currents and longshore currents. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement from late Saturday night through Tuesday morning for Orange County Coastal Areas-San Diego County Coastal Areas. PZ...NONE. && $$ PUBLIC...10/MM AVIATION/MARINE/BEACHES...Maxwell