####018007551#### FXUS66 KLOX 162126 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 226 PM PDT Fri May 16 2025 .SYNOPSIS...16/125 PM. Strong onshore flow and a deep marine layer will bring cool weather through Saturday. Gusty onshore winds are expected in the Antelope Valley during the afternoon and evening. Night through morning drizzle or light rain is possible Saturday. A warming trend will be will begin Sunday and continue through next week as high pressure develops. Temperatures more typical of the summer season are likely away from the coast for the latter half of next week. && .SHORT TERM (TDY-MON)...16/159 PM. An approaching upper level trough is increasing onshore flow and cooling the air mass as well. Highs today cooled 3-6 degrees across most of the area with the exception of interior SLO County, the higher mountains, and the Antelope valley where temperatures warmed by 2-4 degrees. The trough will continue to deepen across California resulting in a higher marine layer tonight, likely up to around 4000 feet, and possibly even some patchy drizzle or very light rain, especially near the south facing coastal slopes. Clearing will slower Saturday and some coast and valley areas may remain cloudy much of the day. There's also a chance of a reverse clearing pattern which would result in more clearing near the coast than inland areas. Temperatures will likely stay in the 60s in most areas, which would be 5-15 degrees below normal. Gusty southwest winds are expected across the Antelope Valley in the afternoon and evening and gusty north to northwest winds are expected across southwest Santa Barbara County. The trough is expected to shift east into the Rockies Sunday as a high pressure ridge over the eastern Pacific moves closer to the coast. A moderate offshore gradient trend will develop leading to 5-10 degrees of warming most areas with either minimal or earlier clearing marine layer. Another round of gusty Sundowner winds expected across southern Santa Barbara County is expected later Sunday afternoon and evening, and this time including eastern Santa Ynez as winds aloft start veer to the north and even slightly northeast. The warming trend will continue Monday with some additional offshore trends leading to some morning northeast winds across the hills and mountains and possibly some of the valleys as well. Expecting widespread warming trends of 5-10 degrees over Sunday and some valley areas as much as 15 degrees warmer, getting close to 90 degrees, including interior SLO County and the western San Fernando Valley. .LONG TERM (TUE-FRI)...16/225 PM. Next week is going to be a hot one and lasting at least two days longer than the previous heat wave. Highs are expecting to be fairly similar to the last heat wave, topping out in the low 100s in the warmer valleys Tuesday through, low 90s in Downtown LA, and 80s across most other areas except the beaches. There may still be a lingering shallow marine layer Monday morning across coastal LA County resulting in some dense fog but that should clear fairly quickly. If the forecast remains on track, and right now confidence is high, another round of heat advisories will be needed for the coastal valleys and possibly even parts of the interior coastal plain. Onshore flow will start to return Thursday that will begin a slow cooling trend into next weekend. && .AVIATION...16/1746Z. At 1640Z at KLAX, the marine inversion was around 3000 feet deep. The top of the inversion was 4500 feet with a temperature of 14 degrees Celsius. High confidence in TAFs for KWJF and KPMD. Moderate confidence in TAFs for remaining sites. There is a 30% chance for IFR to MVFR cigs between 12Z and 18Z at KPRB. Coastal sites forecast to clear have a 30% chance of not clearing, and 30% chance for sites forecast to not clear to SCT. Dissipation of cigs may be off +/- 2 hours, and arrival may be off +/- 3 hours. Minimum flight cat may be off by one cat for KSBP/KSMX. KLAX...Moderate confidence in TAF. There is a 30% chance for cigs to SCT between 20Z and 03Z. Cigs may SCT tomorrow between 20Z and 00Z. There is a 20-40% chance for an east wind component of 8 kts between 11Z and 18Z. Best chances between 14Z and 18Z. KBUR...Moderate confidence in TAF. Return of cigs may be off +/- 3 hours, and there is a 20% chance for cigs 007-009. && .MARINE...16/156 PM. For the Outer Waters through Tuesday, high confidence in combination of Small Craft Advisory (SCA) level winds and seas. For Saturday afternoon through Sunday night, there is a 60-70% chance of Gale force winds. Gales look to be strongest and most widespread Sunday afternoon through late Sunday night. There may be a lull in the winds Sunday morning. Seas will reach 12-14 feet. Rough, short period seas will exist into at least Monday. For the Inner Waters through Sunday night, high confidence in SCA level winds, especially in the afternoon and evening hours. There is a 50-60% chance of Gale force winds Saturday afternoon through Sunday evening, with a lull in the winds likely late Saturday through Sunday morning. Another Gale Warning is likely for Sunday afternoon and evening. For Monday through Tuesday, there is a 50-70% chance of SCA level winds continuing. Seas will reach 10-12 feet. Rough, short period seas will exist into Monday. For the Inner Waters south of Point Conception through Saturday morning, high confidence in winds and seas remaining below SCA levels. For Saturday afternoon through Sunday night, high confidence in SCA level winds focused mostly through the Santa Barbara and western sections of the southern Inner Waters. Additionally, there is a 50% chance of Gale force winds across the Santa Barbara Channel Saturday evening through Saturday night. There will be a relative lull in the winds overnight, then another Gale Warning is likely (50-60% chance) for the Santa Barbara Channel Sunday afternoon into late night. Seas may approach 8 feet with short periods due to the wind. For Monday through Tuesday, moderate confidence in winds and seas remaining below SCA levels. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect from 10 AM to 9 PM PDT Saturday for zones 381-383. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 9 PM PDT this evening for zone 645. (See LAXMWWLOX). Gale Warning in effect from 3 PM Saturday to 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from noon to 6 PM PDT Saturday for zone 650. (See LAXMWWLOX). Gale Warning in effect from 6 PM Saturday to 3 AM PDT Sunday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 6 PM Saturday to 3 AM PDT Sunday for zone 655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 PM PDT Saturday for zones 670-673-676. (See LAXMWWLOX). Gale Warning in effect from 3 PM Saturday to 3 AM PDT Monday for zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...MW AVIATION...Lewis MARINE...Lewis SYNOPSIS...MW/Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox ####018006052#### FXUS66 KPDT 162129 AFDPDT Area Forecast Discussion National Weather Service Pendleton OR 229 PM PDT Fri May 16 2025 .SHORT TERM...Tonight through Sunday night... Key Messages: 1. Showers and a 10-30% chance of thunderstorms tonight through Sunday. 2. Breezy to windy conditions through the Cascade gaps and across portions of the Columbia Plateau Saturday and Sunday. 3. Light snowfall for mountain passes Saturday night and Sunday morning. Tonight, the first of back-to-back waves is expected to arrive from the northeast Pacific (>90% confidence). This wave is currently visible on water vapor imagery west of Vancouver Island, diving southeast towards the PacNW. The second vorticity maximum located in the Gulf of Alaska, is not advertised by ensemble NWP to arrive until Saturday night through Sunday, and is the main driver of uncertainty in the short-term forecast; its track will have implications on precipitation and wind. Shower chances will increase tonight, with some weak elevated instability facilitating low-end chances (10-15%) of embedded thunderstorms for portions of central and east-central Oregon, mainly in Grant County. Area-wide shower chances will increase Saturday through Saturday night as the first wave provides ample forcing, and as the second wave digs southeast into the PacNW. Have maintained an area-wide slight chance (15-24% probability) to chance (25-35% probability) mention of thunder in the forecast Saturday. Best chances of thunderstorms will be over the Blue Mountains and their foothills as well as portions of the lower Columbia Basin during the afternoon (25-35% probability) . Delving into clusters of ensemble solutions does reveal some uncertainty in the evolution of the system as the two waves interact Saturday night through Sunday; ensemble members are still uncertain whether the second wave will become a slower-moving closed low overhead late Saturday through Saturday night or if it will remain a weaker open wave trough with a quicker exit through Sunday. Westerly winds will increase in magnitude Saturday afternoon through the Cascade gaps as cross-Cascade pressure differences increase and a robust low-level jet (35-45 kts) sets up. NBM probabilities of exceeding advisory-level gusts (45 mph) through the eastern Columbia River Gorge, Kittitas Valley, and wind-prone portions of the Columbia Basin/Blue Mountain foothills are roughly 40-70%. Saturday night through Sunday, the likelihood of reaching advisory criteria is high (60-95% chance) through the Kittitas Valley and eastern Columbia River Gorge. Moreover, a low-medium chance (30-60%) of warning-level wind gusts (58 mph or greater) is advertised by the NBM for the Kittitas Valley. In other wind- prone portions of the Columbia Basin/Blue Mountain foothills, NBM probabilities of reaching advisory criteria are medium-high (40-70%). Due to the aforementioned uncertainty in the precise track of the second wave, have held off issuing any wind highlights with the afternoon forecast package. Lastly, will mention measurable snowfall (0.1" or greater) is more likely than not (50-85% chance) across mountain passes Saturday night through Sunday morning as colder air associated with the trough/closed low spreads over the region. In fact, NBM probabilities place medium (40-60%) chances of 1" of snowfall or more for the higher passes of the Cascades and Blue Mountains. However, snow accumulation on roadways may be limited due to warm antecedent conditions. Plunkett/86 && .LONG TERM...Monday through Friday...Westerly flow over the area will allow for a weak system to move across the region on Monday. It will bring mainly light rain to the mountains. Lingering moisture in the westerly flow will keep precip chances in the mountains on Tuesday. The rest of the extended period looks to be dry, with some transitory ridging Tuesday into Wednesday and more zonal flow Wednesday into Thursday then more ridging Thursday into Thursday night. Monday and Tuesday will see diurnally breezy winds, with Tuesday possibly breezier. Winds will mainly be in the 25 to 30 mph range in the normally gusty areas such as the Kittitas Valley, Simcoe Highlands, Columbia Basin and Foothills of the Blue Mountains. On Monday, NBM probabilities of wind gusts >= 25 mph is quite high generally 90 percent or greater in these areas. However, the probabilities of wind gusts >= 39 mph is 20 to 50 percent. On Tuesday. NBM probabilities of wind gusts >= 25 mph is about the same as Monday. However, the probabilities of wind gusts >= 39 mph is a bit higher30 to 60 percent and much higher in the Kittitas Valley (80 percent). && .AVIATION...18Z TAFS...VFR conditions are expected through the day today and into tonight. By early Saturday morning, there could be some MVFR conditions at BDN/RDM as SHRA begins to move in. Otherwise SHRA will impact all sites through the period except for PSC, ALW where the best chances of SHRA will occur after 17/18Z. Winds will generally be 10 kts or less except at PDT, where winds will gust around 20 kts this afternoon and DLS who could see some gusts in the 15 to 20 kt range as well and possibly higher. && .PRELIMINARY POINT TEMPS/POPS... PDT 48 64 43 62 / 20 90 70 30 ALW 49 64 44 61 / 10 80 90 40 PSC 48 69 45 69 / 10 70 60 10 YKM 49 69 41 67 / 30 70 10 0 HRI 49 69 44 67 / 20 80 50 20 ELN 47 65 41 61 / 40 80 20 0 RDM 42 62 34 57 / 30 80 20 10 LGD 42 58 39 54 / 30 90 90 50 GCD 43 56 36 52 / 70 100 80 30 DLS 51 68 46 64 / 30 60 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. && $$ SHORT TERM...86 LONG TERM....77 AVIATION...77