Area Forecast Discussion
Issued by NWS Los Angeles, CA

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373 FXUS66 KLOX 192052 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 152 PM PDT Wed Jun 19 2024 .SYNOPSIS...
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19/1254 PM. Onshore flow will maintain near-normal temperatures across the region through Thursday with overnight low clouds and fog along the coast and valley areas. Expect warming beginning on Friday with above normal temperatures, especially in the interior where dangerously hot weather is possible over the weekend.
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&& .SHORT TERM (TDY-SAT)...
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19/136 PM. Synoptically, the area is under an upper-level trough that extends over the western two thirds of the CONUS. By late Friday this feature will have moved to the east and the area will be in a broad area of higher pressure. By Sunday the peak of the high will be located near the four-corners area, a position favorable to transport moisture to the area during the monsoon season, and models are indicating there is over one inch of perceptible water heading our way with it. This will complicate the temperature forecast and could possibly lead to some afternoon mountain showers although they are not currently indicated. Higher heights will remain in place throughout the week until another trough drops down the California coast on Friday. Temperatures are currently 2-4 degrees cooler along the coast with stronger onshore flow along the south coast and some lingering marine clouds. Heights are also a bit lower today. Onshore flow ad the LAX-DAG gradient is up to 5.3 and this may keep some south coast beaches cloudy all afternoon. Still expecting strong NW winds coming off the waters of the Central Coast to filter through the Western Santa Ynez range and produce low end advisory level gusts across the western half of the SBA south coast this afternoon and evening. Two competing forces will be at work on the marine layer cloud pattern on Thursday as increasing troffing aloft combines with the eddy to promote cloud development. On the other hand sfc gradients will be weaker than they are this morning. Short range ensemble guidance shows that the eddy will likely be weaker and this should tip the scales to a clearer forecast. The best chance for low clouds will be over the southern portion of LA county and the Central Coast. Added in more low clouds for Oxnard plain through Burbank for tomorrow based on latest model guidance. The offshore trends will delay and weaken the seabreeze and this will bring 2 to 3 degrees of warming to the area with the exception of the Central Coast which will cool due to a more robust marine layer presence. The Summer Solstice will occur at 151 PM PDT. Friday will kick off a fairly dramatic warm up as a large and hot upper high over the middle of the county expands westward. The eddy looks a little stronger so probably a little more morning low clouds across the coasts and into some of the lower vlys. By noon the whole area will be clear. Heights will climb to ~588 dam and max temps will warm 5 to 10 degrees across the interior and 2 to 4 degrees across the vlys. The coasts will still be under the marine influence and max temps will not change much. Antelope Vly residents will see max temps range from 100 to 103 degrees or about 8 degrees over normal, and The Paso Robles area will also near the 100 degree mark. Saturday should be the hottest day of the heat event as SoCal will be covered by the western half of an upper high`s western half. Heights will rise to ~591 dam, but the fairly strong onshore flow will remain in place resulting in a strong temperature gradient from the coasts to inland. The high hgts will really snmoosh the marine layer down and create a very strong inversion. Such strong inversions are hard to break down and this could keep clouds at the beach all day long. The marine layer will be under 1000 ft and this will keep it out of most if not all of the vlys. The very steep inversion will also keep min temps much warmer than normal right at the top of the inversion so locations near 1000 ft in elevation will see these very warm overnight lows. Look for 3 to 6 degrees of warming on Saturday away from the beaches. Max temps across the interior will end up 6 to 12 degrees above normal while the vlys will be 2 to 4 degrees above normal. There is about a 10% chance of 1" PWAT reaching into LA County by Saturday afternoon. This moisture could impact the Saturday night to Sunday marine layer, and overnight min temps. .LONG TERM (SUN-WED)...19/152 PM. Blended ensemble guidance shows some cooling on Sunday which could be a reflection of the PWAT which is up to a 60% chance of more than 1" by Sunday afternoon. The NAEFS forecast values for PW are in the 90th to 99th percentile over Los Angeles County basically from Sunday through Tuesday. This moisture will affect the marine layer and temperature forecasts. There is even a small (10-20%) chance of afternoon showers over the mountains. The higher heights persist over the area Monday through Wednesday but the broader area moves to the west and this position will turn off the moisture to the area by late Tuesday. The temperature differences will continue with the coasts sitting near normal with a stubborn night through morning low cloud pattern in place and the interior seeing well above-normal temps.
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&& .AVIATION...19/1753Z. At 17Z at KLAX, the marine layer was 2500 feet deep. The top of the inversion was at 4200 ft with a temperature of 17 deg C. High confidence in 18Z TAFs for KPRB, KPMD and KWJF. Moderate confidence in all other 18Z TAFs. Flight cat changes may be off by +/- 1 hour this morning for airfields with low clouds at start of fcst period, and +/- 3 hours tonight. Cig hgts may be off by +/- 300 ft. There is a 30% chance of no cigs tonight into Thu morning at KBUR and KVNY. KLAX...Moderate confidence in TAF. There is a 20% chance of BKN008 cigs from 05Z-12Z Thur. Any east wind component should be less than 6 knots. KBUR...Moderate confidence in TAF. There is a 30% chance of no cigs tonight into Thu morning. && .MARINE...
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19/1253 PM. For the Outer Waters, high confidence in current forecast. Small Craft Advisory (SCA) winds are expected through Friday night. Brief lulls in the winds during the mornings hours are possible. Seas will be steep and choppy through Friday night. Conditions are then expected to be below SCA levels Saturday through Monday night. For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. SCA winds and choppy seas will persist through tonight, and again Thursday afternoon and evening. For Friday through Monday night, winds and seas should remain below SCA levels. For the inner waters south of Point Conception, moderate to high confidence in current forecast. For the western Santa Barbara Channel, winds gusts will be at SCA levels each afternoon and evening through Thursday. There is also a 30% chance of SCA level wind gusts at times for western portions of the southern inner waters Thursday evening. Elsewhere and otherwise over the southern inner waters, winds and seas should remain below SCA levels through Monday night.
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&& .LOX WATCHES/WARNINGS/ADVISORIES...
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CA...Wind Advisory remains in effect until 3 AM PDT Thursday for zones 349-351. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Friday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zones 670-673-676. (See LAXMWWLOX).
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&& $$ PUBLIC...Rorke/jld AVIATION...Sirard MARINE...Sirard SYNOPSIS...jld weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox