Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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991 FXUS66 KLOX 171208 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 508 AM PDT Tue Sep 17 2024 .SYNOPSIS...16/841 PM. Much cooler than normal temperatures will continue through Friday before warmer conditions return for the weekend. There is a chance of rain or drizzle Wednesday night and Thursday as a low pressure system moves into the area. && .SHORT TERM (TDY-THU)...17/242 AM. A fairly unusual pattern for mid September as Srn CA is in between a departing upper low and an approaching upper low. All of the cold air form ydy`s low destroyed the marine inversion and low clouds are confined to western SBA county. Rising hgts, plenty of sunshine and weak onshore flow will bring 2 to 4 degrees of warming to the csts/vlys and 4 to 8 degrees for the mtns and interior. Despite this warming max temps will end up 10 to 15 degrees blo normals. The next upper low will start its trek down the west coast early Wednesday and by noon it will be just west of the Bay Area. The marine inversion should reform and this along with stronger onshore should allow for a little more coastal stratus to form esp for the Central Coast and the LA cst. A slight chc of rain will develop in the afternoon over SLO county as the low moves further south. Max temps will warm a degree or two south of Pt Conception and will cool a degree or two north. The low with 563 dam central hgt will continue to move south overnight and by dawn Thursday it will be centered just to the north of SLO county. A chance of rain will overspread SLO And SBA counties overnight. There is a slight chc of rain for VTA and LA counties but more likely the upper low will gin up a deep marine layer cloud deck and some drizzle (which could produce a few of an inch) Rainfall amounts overnight will not total any more than .05 inches. The upper low will skirt along the northern portion of the forecast area on Thursday. It will bring cloudy skies and chc of rain to the entire area. The system does not have much moisture to work with and rainfall amounts will be under a tenth of an inch with the only exception being the NW corner of SLO county which could see a quarter inch. The cold core of the upper low will move over the area in the afternoon and the instability created by the cold temps aloft could be enough for TSTM development. At this time there is only a 10 percent chc of a TSTM but the threat will need monitoring. Max temps on Thursday will plummet along with the quickly lowering hgts and cloud cover. Look for 4 to 8 degrees of cooling across the board with max temps coming in 10 to 20 degree blo normals. Look for max temps in the 60s across the coasts and 70s in the vlys. Breezy northwest to onshore winds are likely Wednesday into Thursday with the most wind prone areas potentially reaching advisory levels. .LONG TERM (FRI-MON)...17/312 AM. All signs point to a robust warming trend starting on Friday. Both the GFS and EC show a rapid rise in hgts to 588 or even 590 dam. At the same time onshore flow weakens considerably with a possibility of weak offshore flow during the morning hours. Marine layer clouds will likely be confined to western SBA county. 6 to 12 degrees of warming is on tap for Friday with 5 to 10 additional degrees slated for Saturday. Sunday will be warmer still but only be 1 or 2 degrees. Slight cooling is forecast Monday as the hgts fall and onshore flow increases. The weekend temps will be 4 to 8 degrees above normal with 70s at beaches 80s a little further inland and 90s in the vlys, lower elevation mtns and inland areas. && .AVIATION...17/0656Z. At 0541Z at KLAX, the marine layer was 4600 feet deep. The top of the weak marine inversion was near 9000 feet with a temperature around 8 degrees Celsius. High confidence for TAFs at KPMD and KWJF. Low-moderate confidence in all remaining TAFs. Sites north of Point Conception have the best chance for cigs and there is a chance for LIFR cigs/vsbys at KSMX (30%) between 10Z and 16Z. Cigs may oscillate between flight categories tonight into Tuesday morning. KLAX...Moderate confidence in TAF through 18Z. There is a chance for MVFR conditions from 12Z to 14Z, however the more likely solution appears to be VFR conditions through until Tuesday night. No significant east wind component expected. KBUR...Low to moderate confidence in TAF due to potential for brief MVFR cigs around 15Z. && .MARINE...17/342 AM. For the Outer Waters (Central Coast to San Nicolas Island), moderate to high confidence in the forecast. For the northern zone (Pt Piedras Blancas to Pt Sal) winds are likely to remain below SCA level through this morning, and current SCA looks on track for gusty winds this afternoon/tonight. From Wednesday afternoon thru Monday, moderate confidence in winds remaining below SCA levels. For the southern zones (Pt Sal to San Nicolas Island) moderate to high confidence in SCA level winds persisting into early Wednesday. There is a 40-60% chance of SCA winds continuing thru late Wed, with the strongest winds shifting to the waters south of Point Conception. There is a 30-60% chance of SCA level winds Thursday thru Monday, with best chances Fri afternoon thru late night. For the Inner Waters off the Central Coast, the current SCA looks on track for this afternoon thru this evening hours. Moderate to high confidence in winds being sub advisory Wednesday thru Friday morning, with another chance for SCA level winds Friday afternoon/evening. There is a 10-20% chance for SCA winds each afternoon/evening Saturday though Monday. For the Inner Waters south of Point Conception, steep, choppy seas linger this morning. Gale force winds have ended, and the current SCA looks on track for the Santa Barbara Channel this afternoon/evening. SCA level winds should reach the Ventura coast by the late afternoon hours. There is a 30-40% chance in SCA level winds returning Wed afternoon/night, but SCA winds are more likely to be limited to the western portions of the zone (PZZ650) and near Santa Cruz Island. From Thurs to Sun, There is a 20-50% chance of SCA level winds in the afternoon thru evening hours, with highest confidence Fri. For the nearshore waters off the Los Angeles and Orange County coasts, Moderate to high confidence in winds remaining below SCA level Tues afternoon thru Sun. && .BEACHES...16/927 PM. A series of Southern Hemispheric storms will send a long-period, South to Southwest swell (around 18-second wave periods) to the Southern California coastal waters through the middle of this week. Wave periods will gradually shorten to around 15 seconds by late week. This S to SW long-period swell will bring an extended period of elevated surf -- surf heights of 4-6 feet -- along with powerful and dangerous rip currents (over 80% chance) through Thursday. The area of greatest concern for these impacts will be across beaches with highest exposure to S to SW swell directions -- especially across the L.A. and Ventura County beaches. These factors warrant the issuance of a Beach Hazards Statement for the L.A. and Ventura County beaches. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Wednesday for zones 645-650-670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Wednesday for zones 673-676. (See LAXMWWLOX). && $$ PUBLIC...Rorke AVIATION...Phillips MARINE...Phillips/JB BEACHES...Phillips/Lund/JMB SYNOPSIS...MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox