FXUS66 KLOX 190632 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 1132 PM PDT Thu Jul 18 2024 .SYNOPSIS...18/909 PM. A significant heatwave will impact Southern California Friday into next week. A large portion of the mountains, foothills, and valleys away from the coast will experience dangerously hot conditions, and very warm temperatures may extend toward the coast. Gusty Sundowner winds will affect portions of southern Santa Barbara County through Saturday night. Monsoonal moisture will potentially bring thunderstorms to the interior mountains and valleys each afternoon into next week. && .SHORT TERM (TDY-SAT)...18/958 PM. ***UPDATE*** Southerly upper level flow keeps moisture in the area as high pressure remains over Arizona and low pressure remains off the coast. There is a weak upper level low expected to approach the region Friday morning, helping keep stronger southerly flow over the area. Temperatures today varied dramatically between the coasts and interior areas. Decent onshore flow along with morning marine layer clouds kept the Central Coast in the upper 50s on the immediate coast, to 60s and low 70s into the coastal plains. Other coastal areas were also cooler from the mid 60s to low 70s. Further inland away from the marine layer influence, temperatures warmed into the 80s and 90s, with mid 100s for the deserts. Heading into tomorrow, expecting temperatures along the coasts to be similar to today, with 2-6 degrees of warming over the interior. Highs for the interior will reach the upper 90s to 100s, where we have Excessive Heat Warnings out, and pushing the 90s to low 100s. Current Excessive Heat Warnings and Heat Advisories look on track. Highs for Friday and Saturday were cooled 4-7 degrees for the coasts and coastal plains with continued onshore flow and morning marine layer clouds expected. Winds become breezy near the coasts Saturday, which should also limit warming in those areas. The marine layer should shrink into Friday morning as heights rise by 2 dam, leading to additional warming. By Saturday, heights reach 594 dam to 596 dam, potentially leading to dense fog near the coasts and more warming closer to coastal areas. Sundowner winds have developed over the western portions of the Santa Barbara south coast, with gusts of 25 to 40 mph expected. Could see winds briefly reach near 45 mph, but thinking wind advisories will not be needed for the area. Expecting to see Sundowner winds redevelop Friday night, likely reaching advisory levels Saturday night. ***From Previous Discussion*** The ridge of high pressure will continue to bring in moisture from the south, increasing PWATs to 1.0-1.5 inches, which will bring a less than 20 percent chance of thunderstorms and monsoonal rain showers to the Los Angeles County interior mountains and deserts (thanks to orographic lifting) each day in the short term, especially during the afternoon and early evening hours. Temperatures are currently 5-7 degrees above this time yesterday (except along the immediate coast) as we enter another extended round of dangerously hot weather. While not quite as hot as the last heat wave, temperatures will increase several degrees each day. The Western Santa Ynez Range and Southwestern Santa Barbara Coast will see gusty NW Sundowner winds this evening thanks to a -2 mb SBA to SMX pressure gradient tonight which will be very similar to last night which brought gusts of 40 mph to locally 45 mph. Beginning Friday, there are Excessive Heat Warnings and Heat Advisories for a majority of the mountains, valleys, and far interior areas which will last through at least the weekend. The immediate coastal areas (esp south of Point Conception) may see limited change each day as a shallow marine layer each day will remain present. Friday night's SBA to SMX pressure gradient will strengthen to around -3 mb so wind advisories may be needed for for wind gusts of 45 to 50 mph winds. On Saturday a weak low pressure system to our west will move over Santa Barbara and San Luis Obispo County, which may result in a slight cooling across the Central Coast. Saturday also brings the highest chances for thunderstorms over the weekend as the moisture keeps building in. However, the chances are still too small to be added into the official forecast at this time. Saturday night's SBA to SMX pressure gradient will increase again, potentially to -4.4, so wind advisories may be needed again for wind gusts of 45 to 50 mph winds. By Sunday, temperatures should climb to 105 to 112 degrees across the lower mountains and far interior areas (including the Antelope Valley), 95 to 105 across the warmest coastal valleys, while areas closest to the coast will range in the upper 60s to high 70s degrees. These temperatures will increase to 5 to 15 degrees above normal as you move away from the coast. .LONG TERM (SUN-WED)...18/211 PM. The long-duration dangerously hot conditions will continue through at least Wednesday, at least for the interior mountains and far interior areas. Temperatures will remain fairly similar day-to-day Monday through Wednesday as not much will change synoptically. Nights will remain very warm across the far interior, with forecast lows to be in the 70s to 80s, resulting in little overnight relief and potentially worsen heat impacts. On Thursday a trough should drop down the west coast and temperatures should drop for the later portion of the week. The potential for daily monsoonal thunderstorms and locally heavy showers continues into mid-week. While the moisture continues to increase and expand across the area early next week, confidence remains low this far out and PoPs remain below 15% for now. If thunderstorms were to form, they will likely form over the higher terrain and interior valleys of Los Angeles and Ventura Counties and possibly extend into Santa Barbara County by early next week. && .AVIATION...19/0616Z. At 05Z at KLAX, the marine layer was 1100 feet deep. The top of the inversion was at 3900 feet with a temperature of 29 Celsius. High confidence in CAVU TAFs for KPRB, KBUR, KVNY. High confidence in TAFs for KPMD and KWJF. Low confidence in all coastal TAFs. Flight categories to be off by one category for all coastal sites through Friday morning. VFR conditions expected at all sites by 21Z, however many may clear by 18Z. Flight category changes may vary by +/- 3 hours from current forecasts. KLAX...Low confidence in TAF. There is a 40% chance for cigs below 005 until 15Z. There is a 10% chance for cigs below 002 and/or vsbys AOB 1/4SM until 15Z. High confidence in cigs dissipating by 18Z at the latest. Flight category changes may be off +/- 3 hours from current forecast. No significant east wind component expected. KBUR...High confidence in CAVU TAF. && .MARINE...18/908 PM. For the outer waters, Small Craft Advisory (SCA) northwest winds are ongoing and are expected to continue through this weekend. There is a 70% chance of low end Gale Force winds to impact the outer waters this weekend. A Gale watch is in effect from Saturday afternoon through Sunday night. Winds will likely taper off Monday, but there is a 50% chance of SCA winds Monday through early next week. Steep seas will also impact the outer waters beginning Friday through at least Monday. For the inner waters north of Pt. Sal, northwest winds are expected to reach SCA levels starting Friday afternoon and continuing into Sunday night. The strongest winds are expected during the later afternoon and evening hours each day. There is a 30% chance that SCA winds don't occur Friday, but they are much more likely Saturday and Sunday (70%). Steep and hazardous seas are expected Friday afternoon into the weekend. For the inner waters south of Pt. Conception, NW to west winds are expected to remain below SCA levels in the Santa Barbara Channel overnight. Winds will increase for Friday afternoon through this weekend in the Santa Barbara Channel. A SCA is in effect starting tomorrow at 2 PM and lasting through Sunday night, primarily impacting the western portion. There is a 30% chance that winds will remain below SCA level in the Santa Barbara Channel Friday afternoon/evening. SCA winds are far more likely Saturday and Sunday (60%). In the furthest southern inner waters, there is a 30% chance for SCA northwest winds to occur over the waters off of the Los Angeles and Orange County coasts Saturday and Sunday. The highest chances are during the afternoon and evening hours across the San Pedro Channel, and west of Catalina Island. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning remains in effect from 10 AM Friday to 10 PM PDT Wednesday for zones 38-88-344-345-351>353-371-372-376>383. (See LAXNPWLOX). Heat Advisory remains in effect from 10 AM Friday to 10 AM PDT Sunday for zones 342-343-369-370-374-375. (See LAXNPWLOX). Excessive Heat Watch remains in effect from Sunday morning through Wednesday evening for zones 342-343-369-370-374-375. (See LAXNPWLOX). Heat Advisory remains in effect from 10 AM Friday to 9 PM PDT Saturday for zones 373-548. (See LAXNPWLOX). PZ...Small Craft Advisory in effect from 2 PM Friday to 11 PM PDT Sunday for zones 645-650. (See LAXMWWLOX). Small Craft Advisory in effect until 2 PM PDT Saturday for zones 670-673-676. (See LAXMWWLOX). Gale Watch in effect from Saturday afternoon through Sunday evening for zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Phillips/Lund AVIATION...Lewis MARINE...Lewis SYNOPSIS...Smith weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox