FXUS66 KLOX 010337 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 837 PM PDT Sat Aug 31 2024 .SYNOPSIS...31/811 PM. High pressure aloft is expected to strengthen over the region through the weekend, and through much of the coming week. Low clouds and fog will affect coastal areas during the overnight to morning hours through the next couple of days. Temperatures are expected to increase by a few degrees each day, with hazardous heat developing mid next week across most areas away from the beaches. && .SHORT TERM (SAT-TUE)...31/834 PM. ***UPDATE*** Temperatures today were slightly below normal for coastal areas, and a few degrees above normal away from the coast. Low clouds early in the day were most widespread over the Central Coast and adjacent coastal valleys, and this area was the slowest to clear in the afternoon. Expect to see a repeat of widespread coverage over the Central Coast tonight into early Sunday, but with much more patchy coverage for coastal areas further south. Winds are currently gusting 25 to 35 mph from the northwest to north over SW Santa Barbara County, and onshore/southwest winds are gusting 20 to 30 mph through the interior passes and canyons of L.A. County into the Antelope Valley. Temperatures are expected to warm by several degrees again on Sunday, with continued above normal highs for inland areas, and closer to normal temperatures for the coasts. Onshore winds could increase some in the afternoon to evening hours as the LAX to Daggett surface pressure gradient bumps up, but they will likely decrease the following couple of days as gradients weaken again. Sundowner winds are also likely to increase some Sunday during the late afternoon to evening hours. ***From Previous Discussion*** As a weak low pressure system travels eastward across the Oregon/California border, 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...31/2347Z. At 2254Z at KLAX, the marine inversion was 1200 feet deep. The top of the inversion was at 3500 feet with a temp of 2900 degrees Celsius. High confidence in 00Z TAFs for KPRB, KBUR, KVNY, KPMD, and KWJF. There is a 10% chance of brief IFR-MVFR cigs/vsbys between 13Z and 15Z at KPRB, KBUR, and KVNY. Moderate confidence in 00Z LA county coastal TAFs. Arrival of cigs may be off +/- 3 hrs from current fcst. Cigs may arrive as MVFR and bounce between IFR-MVFR thru the period. There is a 10% chance of brief LIFR cigs/vsbys between 09Z and 14Z. Moderate confidence in 00Z TAFs for remaining coastal sites. There is a 40% chance for LIFR conds once cigs arrive at KSBP, KSMX, KOXR, and KCMA. Arrival of cigs may be off +/- 3 hours from current fcst. KLAX...Moderate confidence in 00Z TAF. There is a 20% chance of cigs arriving as early as 02Z and a 30% chance that cigs arrive BKN010 or higher. There is a 10% chance of brief OVC004 between 09Z and 14Z, but IFR-MVFR cigs/vsbys are most likely. There is a 30% chance of VFR conds by 16Z. No significant east wind component is expected. KBUR...High confidence in 00Z TAF. There is a 10% chance of brief cigs between 006-011 and/or vsbys 4-5SM between 13Z and 15Z. && .MARINE...31/834 PM. For the Outer Waters from the Central Coast to San Nicolas Island, moderate to high confidence in current forecast. Tonight through late Monday, high confidence in Small Craft Advisory (SCA) level winds, especially in the southern two zones from Pt Sal to San Nicolas Island. Moderate confidence in winds and seas remaining below SCA level Tuesday and Wednesday, however there is a 20-30% chance of low end SCA level winds developing in the southern two zones in the afternoon thru evening hours on Tuesday and Wednesday, especially near the western side of the Channel Islands. For the Inner Waters north of Point Sal, moderate confidence in the current forecast. Winds are continuing to decrease tonight, but there is a 40-50% chance of SCA level winds in the afternoon thru evening hours Sunday and Monday. Higher confidence in winds and seas remaining below SCA level Tuesday and Wednesday. For the Santa Barbara Channel, moderate to high confidence in current forecast. SCA level winds are likely (50-60% chance) in the extreme Western Portion of the Channel in the afternoon thru evening hours Sunday and Monday. High confidence in winds and seas remaining below SCA level Tuesday and Wednesday. For the Eastern Portion of the Channel, high confidence in conditions remaining below SCA level thru Wednesday. For the inner waters off the Los Angeles and Orange County coasts, high confidence in conditions remaining under SCA levels through Wednesday. 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 midnight PDT tonight for zones 645-650. (See LAXMWWLOX). 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...Lewis MARINE...Lewis/RAT SYNOPSIS...Cohen/Schoenfeld weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox