543 FXUS66 KLOX 052209 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 209 PM PST Sat Dec 5 2020 .SYNOPSIS...05/205 PM. Clear to partly cloudy skies and dry weather will prevail for at least the next seven days. High temperatures will be a little warmer than normal and most lows will be a few degrees lower than normal. There will be moderate to strong Santa Ana winds Monday through Tuesday morning. && .SHORT TERM (TDY-TUE)...05/204 PM. Mostly sunny skies covered the forecast area early this afternoon with little change expected thru sunset except a few hi clouds should move into SLO/SBA Counties. Offshore pressure gradients to the E continued early this afternoon (20Z LAX-DAG was -3.1 mb). Breezy NE winds prevailed over portions of the foothills and mtns of VTU/L.A. Counties, with local gusts up to 25 mph. These winds will persist thru sunset, while elsewhere breezy onshore flow can be expected. The offshore gradients will help many areas away from the coast to lower mtns to top out in 70s to around 80 this afternoon, which are about 5 to 10 deg above normal for this time of year. A weak upper level trof will prevail over SW CA this afternoon, with H5 heights around 578 dm. Upper level ridging should build in tonight into Sun, with H5 heights rising to around 581 dm by late Sun morning. A 562 dm upper level low is forecast to develop over nrn NV on Sun, then track S Sun night into Mon morning. The dry upper level low will reach L.A. County by 21Z Mon before moving off the coast S of the area by late Mon. This system will move to a position off the nrn Baja coast Mon night then remain nearly stationary thru Tue. There may be some hi clouds over the area at times thru Mon, otherwise mostly clear skies should prevail thru Tue. Marine layer clouds should remain off the coast thru Sun, altho patchy low clouds and fog cannot be entirely ruled out along the immediate Central Coast thru Sun morning. Increased offshore flow will then push any low clouds well off the coast later Sun night into Mon then continue thru Tue. Pressure gradients will be weaker offshore to the N and E tonight into Sun, then strengthen Sun night into Mon. By 12Z Mon, the NAM forecasts the LAX-DAG gradient to be around -5.4 mb, with LAX-BFL around -4.7 mb. Breezy offshore flow can be expected tonight and Sun morning, especially for the foothills and mtns. The increased offshore gradients combined with some cold air advection and upper level support will bring strong and gusty NE winds to the mtns and some vlys by early Mon morning. The winds should remain quite gusty thru Mon afternoon as the offshore gradients increase further. Further strengthening of the winds can be expected Mon night into Tue morning as offshore gradients to the N and E are forecast by the NAM to increase by 12Z Tue to -8.9 mb from LAX- DAG, and to -7.3 mb from LAX-BFL. 850 MB winds over VTU/L.A. Counties are forecast to increase to 45-50 kt Mon into Tue, with 950 mb winds forecast to peak around 50 kt Mon morning, and around 50-55 kt late Mon thru Mon night. Significant 850 mb winds will also affect SLO/SBA Counties and increase out of the east up to 40 kt later Mon and Mon night. Damaging wind gusts up to 60 to 70 mph will be possible at times for the mtns of VTU/L.A. Counties including the Santa Monica Mtns from late Sun night thru midday Tue. A High Wind Watch will be issued with the afternoon zones for these areas. Widespread high- end Wind Advisories will eventually be needed for the rest of VTU/L.A Counties, except for the Antelope Vly, from Mon morning thru Tue morning, and possibly for the SLO/SBA County mtns from Mon afternoon thru early Tue morning. High temps across the region are forecast to remain quite mild and several degrees above normal for many areas Sun. Temps should cool some for the mtns and deserts on Mon, while S of the mtns it should be a few degrees warmer with the increased offshore flow and adiabatic warming. Highs in the vlys and coastal areas should reach the 70s Sun, and mostly in the mid to upper 70s on Mon. Temps Tue S of the mtns should warm up another 5 to 10 deg and reach the low to mid 80s for a lot of the coast and vlys. There will also be cold overnight lows in sheltered areas. Lows should fall into the mid teens to lower 20s in the Antelope Valley tonight where a Hard Freeze Warning will be issued. .LONG TERM (WED-SAT)...05/159 PM. The upper level low off Baja will slowly move E Tue night and Wed while weak upper level ridging builds into the forecast area. Flat upper level ridging will linger Thu and Fri. The EC builds in stronger upper level riding into the area by Sat, while the GFS keeps weak flat upper ridging over the region. The mean ensembles forecast weaker upper level ridging for Sat. Offshore gradients to the N and/or E will persist thru the extended period. Dry weather will continue Wed thru Sat over SW CA with mostly clear skies thru the period. Breezy offshore flow can be expected night and morning hours, altho may be weak to light onshore on Fri, and a little bit stronger on Sat. Temps will be warmest on Wed, about 5-10 deg above normal for many areas, then cool slightly thru Sat but still remain a few degrees above normal each day, especially S of the mtns. && .AVIATION...05/1749Z. At 17Z at KLAX, there was no marine layer. The surface based inversion top was at 1000 feet and 17 degrees Celsius. There is a 20 percent chance of LIFR FG impacting KSMX Sunday 10-16Z. Otherwise, high confidence in VFR everywhere with weaker than normal winds. Widespread moderate to strong northeast winds will develop Monday and Tuesday. KLAX...High confidence VFR conditions through Sunday, with no significant east winds. KBUR...High confidence VFR conditions through Sunday. && .MARINE...05/101 PM. High confidence in winds staying below Small Craft Advisory (SCA) through early Sunday morning. High confidence in SCA winds from the Central Coast to San Nicolas Island forming by Sunday afternoon and continuing through the night. High confidence of northeast winds forming over most waters on Monday, and moderately confident that they will become unusually widespread and gusty by Monday afternoon or evening...then gradually weakening Tuesday and Wednesday. There is a 50 percent chance for Gale Conditions from Ventura to Santa Monica from Monday afternoon through Tuesday morning. Otherwise expecting solid SCA winds and seas over most if not all zones, including the Central Coast and possibly Avalon Harbor. Meanwhile, a large long period west to northwest swell will impact all waters Monday through early Wednesday, lowering but staying elevated through the rest of the week. Tuesday will be the largest, when swells will range from around 15 feet off the Central Coast, to around 7 feet from Santa Barbara to Orange County. This will create hazardous breaking waves near shore, possibly including the Morro Bay and Ventura Harbor entrances. While this long period swell will be dominant, it is worth mentioning that there will also be short period waves on top of this swell when and where the gusty NE winds (mentioned above) are blowing. && .BEACHES...05/1237 PM. A very large and long period west to northwest swell will impact the area later Monday through early Wednesday. The forerunner waves will have periods longer than 20 seconds Monday afternoon and night, Breaking waves between 15 and 20 feet are possible on the Central Coast during the Tuesday peak, and 6 to 12 feet for Los Angeles, Ventura and parts of southern Santa Barbara Counties. Surf of 20 feet and greater can damage coastal structures like piers and jetties, so a High Surf Warning may be required for the Central Coast. Otherwise, expecting High Surf Advisories with dangerous rip currents at most beaches. Widespread northeast to east winds are expected during this time as well, especially Monday afternoon and night which could amplify some waves. Vulnerable harbor entrances, like Morro Bay and Ventura, have a history of dangerous breaking waves under such conditions. High tides should stay below 5 feet during the event, so the threat of coastal flooding is minimal. && .FIRE WEATHER...05/933 AM. Red flag warnings remain in place today over the mountains of Los Angeles and Ventura Counties, and the Santa Clarita Valley due to northeast to east winds gusting 20 to 30 mph coupled with very low humidities of 5 to 10 percent. Offshore winds will continue to decrease tonight and Sunday. A cold low pressure system over Nevada on Sunday night will dive southwestward through Southwest California on Monday, shifting to the south of the area by Monday night. This system will likely bring increased higher level clouds and an uptick of surface humidities through Monday morning, then a drying trend by Monday afternoon into Tuesday when humidities in the teens and single digits will be common. Gusty Santa Ana winds will likely develop late Sunday night into Monday morning, then peak in coverage and strength Monday afternoon into Tuesday morning when wind gusts of 40 to 55 mph will be common across the wind favored coastal and valley areas of Los Angeles and Ventura counties, and damaging gusts of 55 to 70 mph possible in the mountains. Also of note with this upcoming event is that the upper level wind support will likely bring unusually strong northeast to east winds across portions of Santa Barbara and San Luis Obispo counties, especially in the mountains and foothills, where wind gusts of 40 to 60 mph will be possible from Monday afternoon through Tuesday morning. Widespread critical fire weather conditions will be likely with this event for Los Angeles and Ventura counties, and possibly portions of San Luis Obispo and Santa Barbara counties. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement in effect from Monday morning through Wednesday evening for zones 34-35-39>41-87. (See LAXCFWLOX). High Wind Watch in effect from late Sunday night through Tuesday morning for zones 46-53-54. (See LAXNPWLOX). Hard Freeze Warning in effect from midnight tonight to 9 AM PST Sunday for zone 59. (See LAXNPWLOX). Fire Weather Watch in effect from Monday afternoon through Tuesday morning for zones 234-235-239-251-252. (See LAXRFWLOX). Red Flag Warning in effect from 4 AM Monday to 10 PM PST Tuesday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX). PZ...Gale Watch in effect from Monday afternoon through Tuesday morning for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect from noon Sunday to 6 AM PST Monday for zones 670-673-676. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (TUE-SAT). Periods of gusty offshore winds and dry conditions could lead to critical fire weather conditions Monday night and Tuesday or Wednesday, then again by next Saturday. High surf or strong rip currents may create hazardous ocean conditions Monday through Wednesday. Sub-freezing conditions are possible for interior valleys each morning at least through Wednesday. && $$ PUBLIC...Sirard AVIATION...Kittell MARINE...Kittell BEACHES...RK FIRE...Gomberg SYNOPSIS...30/Sirard weather.gov/losangeles