Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000 FXUS66 KLOX 252155 AFDLOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 255 PM PDT Tue Jul 25 2017 .SYNOPSIS...
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There is a slight chance of a thunderstorm or shower in the mountains and deserts this afternoon and evening. Dry southwest flow aloft and a building ridge will gradually warm temperatures this week to a few degrees above normal. Overnight and morning low clouds will continue along the coasts.
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&& .SHORT TERM...
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(TDY-FRI) The remnants of a monsoonal surge remain over the area today as southwest flow aloft continues to entrain drier air into the air mass. Some cumuliform cloud development is taking place over the mountains and desert. With enough moisture still in place, a slight chance of showers and thunderstorms remains in the forecast through this afternoon and evening across the Los Angeles and Ventura County Mountains and the Antelope Valley. High pressure aloft to the east centered over the Texas will start to nudge west through Thursday night and build across the area. An onshore flow pattern should weaken into late week along with a thinning marine layer depth. NAM-WRF time height sections at KLAX reflect the trend well with the near-surface moisture getting squashed each day through Thursday and remaining shallow into Friday. A warming trend should take shape through the end of the work week as 500 mb heights climb across the region. Temperatures could reach toward dangerously hot levels across portions of the area on Friday and a heat advisory could needed Friday for the Los Angeles and Ventura County Mountains, if this trend continues. .LONG TERM...(SAT-TUE) The ridge aloft weakens some while pushing into Northern Arizona over the weekend as the remnant moisture from Hurricane Hilary could get embedded in the flow around the high pressure system. GFS and ECMWF solutions hint at some semblance of an easterly wave moving over the region. A slight chance of showers and thunderstorms remain in the forecast over the weekend over the Mountains and Desert and into early next week as a low confidence forecast looks to develop. Some model differences start to develop over the weekend and into early next week. Both model solutions agree that the high pressure system will strengthen to near 598 dm over the Great Basin some time between Tuesday and late next week. While agreement exists for further warming, timing will be difficult to place as much will depend upon the movement of the remnants of Hurricane Hilary.
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&& .AVIATION...
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25/1800Z. At 1733Z, the marine layer depth was 1550 feet. The top of the inversion was 3200 feet with a temperature of 21 degrees Celsius. Moderate confidence in 18Z TAF package. For tonight, high confidence in return of stratus to coastal sites. There is less confidence in the return of marine clouds to any valley sites. KLAX...Moderate confidence in 18Z TAF. There is a 30 percent chance of the marine clouds arriving plus or minus two or more hours from the forecasted time. KBUR...Low to moderate confidence in 18Z TAF. There is a 40 percent chance of MVFR/IFR CIGs 10Z-17Z.
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&& .MARINE...
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25/200 PM... For the Outer Waters, good confidence in current forecast. Winds and seas will remain below Small Craft Advisory (SCA) levels through Thursday. For Friday and Saturday, winds may increase to SCA levels in the far north portion. For the Inner Waters, good confidence in current forecast. For the waters north of Point Sal, winds and seas are expected to remain just below SCA levels through Saturday. For the waters south of Point Conception, winds and seas will remain below SCA levels through Saturday.
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&& .BEACHES...
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25/200 PM. Hurricane Hilary is expected to become a major hurricane today. As this system continues to strengthen, it will generate a southeasterly swell that will impact Southern California beaches this weekend. The southeasterly swell will move into the coastal waters early Friday, then peak on Sunday. High surf conditions as well as strong rip currents will be likely across south-facing beaches this weekend. Isolated damaging sets of surf and beach erosion cannot be ruled out for the south-facing beaches of Los Angeles and Ventura Counties.
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&& .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && .HAZARD POTENTIAL OUTLOOK...
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(FRI-TUE) A significant surf event could develop late Thursday as swells from Hurricane Hilary arrive at the Southern California beaches. High surf and strong rip currents will occur from Friday through Sunday.
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&& $$ PUBLIC...Hall AVIATION...Sweet MARINE...Sweet BEACHES...Sweet SYNOPSIS...B weather.gov/losangeles

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