FXUS66 KLOX 312227 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 327 PM PDT Sat Aug 31 2024 .SYNOPSIS...31/922 AM. Today is expected to be the coolest day of the week with slightly below normal temperatures at the coasts and a several degrees above normal for interior areas. Low clouds and fog will occur near the coast during the overnight and morning hours into early next week. Temperatures are expected to increase by a few degrees each day, with hazardous heat developing mid next week across most areas besides the beaches. && .SHORT TERM (TDY-TUE)...31/326 PM. As a weak low pressure system travels eastward across the Oregon/California boarder, the upper level pattern for the region is likely to be rather consistent through early next week. Then Tuesday, as the upper low moves farther east, the 4 Corners high pressure will build back over SoCal. Concurrently, onshore pressure gradients will trend downwards each day, with the chance for weak offshore flow beginning Tuesday morning. Temperatures will trend upwards each day by a few degrees, and will be largely at or above normal by Sunday. By Tuesday, moderate HeatRisk will be widespread across areas away from the coast. Expect temperatures in the upper 70s and 80s at the coasts, in the 90s to up to 105 degrees for the valleys and deserts. Low clouds and fog will occur across the beaches during the overnight to morning hours, through Monday morning. By Tuesday most of the region will be cloud free. North- to-south pressure gradients will drive low-level northwest Sundowner Winds across the Santa Barbara Southwestern Coast this evening and again tomorrow evening. Local gusts up to 40 mph possible for wind prone sites such as Gaviota and Refugio. .LONG TERM (WED-SAT)...31/259 PM. By Wednesday the heat event is expected to be well underway, with a persist ridge of high pressure over the region. There is moderate- to- high confidence in temperature forecasts for Wednesday and Thursday, followed by significantly lower confidence Friday onward. There remains a large discrepancy between the GFS and the ECMWF, with the ECMWF favoring more significant offshore flow. A large portion of the ensemble guidance is trending toward the ECMWF scenario, which would yield higher and hazardous heat conditions, especially for mountains and valleys. There is around a 20-30% chance of a weaker ridge and thus lower heat impacts than forecasted. The pattern for this heat event is driven by a warm airmass aloft, warm downsloping flow, and the suppression of the seabreeze. However during September, the sun angle and daytime heating hours are lower than earlier in the summer. Thus temperatures will be highest for the interior valleys, foothills, and mountains. Onshore pressure gradients are likely to trend downwards over LA and Ventura Counties. This will allow for areas of offshore flow in the mid levels, that will transport warm downsloping air into areas such as the western San Fernando Valley and adjacent foothills. Thursday is likely to be the warmest day, with a chance (30 percent) that Friday will be equally warm. Moderate to Major HeatRisk is expected for much of the region at this time, except for the beaches and the Central Coast. There is an 80% chance of heat headlines for most foothill, valley and mountain locations during the Wednesday- Friday time frame, with at least a 50% chance for Excessive Heat warnings for the San Fernando and Santa Clarita Valley. There is greater uncertainty in the exact temperatures Friday onward, as heat starts to wind down. However this is moderate-to- high confidence that heat impacts will be minimal by the end of the next weekend. Most stratus will be confined to the Central Coast, with clear skies most common for the region. The transport of monsoonal moisture is not favored and no precipitation is forecast at this time. && .AVIATION...31/1717Z. At 1700Z at KLAX, the marine inversion was 1000 feet deep. The top of the inversion was at 3900 feet with a temp of 28 degrees Celsius. For 18Z TAF package, high confidence in valley/desert TAFs, but low to moderate confidence in coastal TAFs. Arrival time of stratus/fog to coastal sites could be +/- 4 hours of current forecasts with a 30% chance that CIG/VSBY restrictions will not develop. KLAX...Moderate confidence in 18Z TAF. Timing of return of CIG/VSBY restrictions could be +/- 4 hours of current 08Z forecast. There is a 20% chance that CIG/VSBY restrictions will not develop overnight. No significant easterly wind component is expected. KBUR...High confidence in 18Z TAF as CAVU conditions are expected through the period. && .MARINE...31/211 PM. For the Outer Waters, moderate to high confidence in current forecast. Today through Sunday night, high confidence in Small Craft Advisory (SCA) level winds. For Monday and Tuesday, there is a 30-40% chance of SCA level winds across PZZ670 and a 50-70% chance of SCA level winds across PZZ673/676. For Wednesday, high confidence in winds and seas remaining below SCA levels. For Thursday, there is a 30-50% chance of SCA level winds. For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Monday, there is a 20-30% chance of SCA level winds in the afternoon and evening hours. For Tuesday through Thursday, high confidence in winds and seas remaining below SCA levels. For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. For the western half of the Santa Barbara Channel, there is a 20-30% chance of SCA level winds in the late afternoon and evening today then a 50-60% chance late Sunday afternoon and evening. Otherwise for the Inner Waters south of Point Conception, high confidence in winds and seas remaining below SCA levels through Thursday. Patchy dense fog, with visibilities of 1 nautical mile or less, will impact the coastal waters over the next several days, mainly in the night and morning hours. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3 AM PDT Monday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 PM PDT Monday for zones 673-676. (See LAXMWWLOX). && $$ PUBLIC...Schoenfeld/Munroe AVIATION...RAT MARINE...RAT SYNOPSIS...Cohen/Schoenfeld weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox