Area Forecast Discussion
Issued by NWS Los Angeles, CA

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400 FXUS66 KLOX 221225 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 425 AM PST Thu Feb 22 2018 .SYNOPSIS...22/344 AM. An upper trough tracking to the northeast of the region will bring a slight chance of rain showers with low elevation snow showers this afternoon through early Friday, along with cool and breezy conditions. Dry and cool weather is expected over the weekend. Another trough may bring more widespread rain to the region late Monday through Tuesday night or early Wed, with a more significant storm later n the week. && .SHORT TERM (TDY-SAT)...22/403 AM. Clear skies across the region early this morning. It was rather cold again. Freeze warning are in effect for the Ojai Valley and frost advisories are in effect for the remainder of the VTU County valleys, the San Fernando and Santa Clarita Valleys, the Santa Monica Mountains and the Central Coast and Santa Ynez Valley. A cold and vigorous but moisture-starved upper trough will dig southward from the Pac NW today and through the western Great Basin tonight. Strong height falls and increasingly cyclonic flow should cause some isolated shower activity across the region this afternoon and tonight, with the best chances of showers across the Central Coast, on the northern mountain slopes and across eastern Los Angeles County. Gusty southwest winds will likely reach advisory levels across the L.A. County mountains and the Antelope Valley this afternoon. Gusty northwest winds should reach advisory levels on the Central Coast this afternoon, and in the mtns and adjacent south coast of SBA County from late this afternoon through late tonight. Once the flow turns northwest across the VTU County mountains the evening, expect advisory level winds there. Elsewhere, gusty winds will also affect coastal sections of L.A. and VTU Counties, but winds should remain below advisory levels there. It will be cool across the region today and tonight. Snow levels will be between 3500 and 4000 feet today, then should lower to between 2500 and 3000 feet tonight and Fri morning. Any showers should end in most areas by late tonight except could linger through Fri morning across the eastern mountains of L.A. County, and on the northern slopes of the VTU County mtns in the moist NW flow there. Local snow accumulations of 1 to 2 inches are possible in the mtns, mainly tonight and early Fri. Snow could potentially affect travel on Interstate 5 near the Grapevine tonight and Fri morning. Local snow is possible in the Antelope Valley, though any accumulation should be less than one inch and confined to the foothills. Skies will be partly cloudy in most areas Fri, and max temps will remain at least 6 to 10 degrees below normal in most areas. Winds should drop below advisory levels in most areas by Fri afternoon. Clear skies are expected Fri night and Sat. It will be very chilly, especially where the wind completely drops off. Freeze and possible Hard Freeze Watches will have to be considered for some valley locations, and possibly coastal sections of SLO and SBA Counties. Max temps may edge upward a bit on Sat, but will still be well below normal everywhere across the region. .LONG TERM (SUN-WED)...22/422 AM. A weak upper trough will zip through the eastern Great Basin Sat night and Sun, while a broad NW flow pattern sets up across the region. Heights and thicknesses across the region will rise. Low level flow will be offshore on Sunday, likely all day. Expect several degrees of warming in most areas on Sunday, with temps possibly getting close to normal in coastal and valley areas. Another trough will drop southward from the Pac NW Mon and Mon night, but there are important difference with its track and ultimately how much rain it could bring to the region. The EC is farther west with its track, which allows the system to pick up more in the way of moisture from the Pacific. It also shows it evolving into an upper low near Point Conception and lingering near the region into Wed. The GFS, is not only farther to the east with the system, keeping it across CA, and while it briefly shows the system closing off early Tue, it keeps it progressive. Therefore, with the EC has the upper low near Catalina Island Wed morning, the GFS shows it already in northern Texas. That is quite a difference. The EC would be much wetter than the GFS. Given the general tendency toward inside slider type systems this winter so far, will lean toward the GFS, but will still bump up pops some in most areas Mon night through Tue night. Max temps on Mon should change little from those on Sunday, then some cooling is expected Tue, with a possible rebound in temps Wed if the GFS is correct. For the end of the week, model disagreements continue with the EC again farther west and much wetter with another system poised to affect the region. && .AVIATION...22/1103Z. At 1100Z, there was no marine inversion at KLAX. Overall, moderate confidence in 12Z TAF package. There is a 40% chance of MVFR CIGs developing late this afternoon through tonight as weak system moves across the area. Isolated showers will be possible across the Central Coast as well as the LAX basin late this afternoon through tonight. Gusty west winds will impact coastal TAFs today as well as the desert TAFs. KLAX...moderate confidence in 12Z TAF. There is a 40% chance of MVFR CIGs 21Z-12Z. There is a 15% chance of showers after 00Z. KBUR...moderate confidence in 12Z TAF. There is a 40% chance of MVFR CIGs 21Z-12Z. There is a 15% chance of showers after 00Z. && .MARINE...22/303 AM. For the Outer Waters, moderate confidence in current forecast. Northwest winds will increase today with 70% chance of widespread Gale force winds this afternoon/tonight. So, a GALE WARNING has been issued. From Friday through Monday, 70% chance of Small Craft Advisory (SCA) level winds continuing with a 40% chance of Gale force winds Saturday afternoon/night. For the Inner Waters, moderate confidence in current forecast. For the waters north of Point Sal, SCA level winds are likely (70% chance) today through Monday, especially during the afternoon and evening hours. There is a 30% chance of Gale force winds this afternoon/evening and again on Saturday. For the waters south of Point Conception, 60% chance of SCA level winds from this afternoon through Saturday night, especially across western portions. After a lull on Sunday, SCA level winds are likely again on Monday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Frost Advisory in effect until 9 AM PST this morning for zones 34>36-45-46-88-547. (See LAXNPWLOX). Wind Advisory in effect from 2 PM this afternoon to 9 PM PST this evening for zones 34-35. (See LAXNPWLOX). Wind Advisory in effect from 2 PM this afternoon to 4 AM PST Friday for zones 39-52. (See LAXNPWLOX). Freeze Warning in effect until 9 AM PST this morning for zone 44. (See LAXNPWLOX). Wind Advisory in effect from 10 PM this evening to 10 AM PST Friday for zone 53. (See LAXNPWLOX). Wind Advisory in effect from 10 AM this morning to 10 AM PST Friday for zone 54. (See LAXNPWLOX). Wind Advisory in effect from 10 AM this morning to 10 PM PST this evening for zone 59. (See LAXNPWLOX). PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PST Friday for zones 645-650-655. (See LAXMWWLOX). Gale Warning in effect from 3 PM this afternoon to 3 AM PST Friday for zones 670-673-676. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK (SAT-WED). Widespread freezing temperature and frost are possible early Saturday. Gusty advisory level winds are possible through the Santa Ynez Range and the I5 corridor early Saturday. Low elevation snow possible Monday night into Tuesday creating hazardous driving conditions in the mountains, especially the I5 corridor area. && $$ PUBLIC...DB AVIATION...RAT MARINE...RAT SYNOPSIS...DB weather.gov/losangeles

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