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Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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835 FXUS66 KLOX 300357 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 857 PM PDT Sat Jun 29 2024 .SYNOPSIS...29/855 PM. A significant heatwave will impact a large part of the area for the upcoming week. Temperatures will become dangerously hot across interior areas, where daily highs up to 100 to 105 degrees will be possible, with highs upwards of 105 to 115 possible over interior valleys and foothills including the Antelope Valley. Late in the upcoming week, temperatures could reach records at some locations, and very warm to hot conditions could extend closer to the coast. Also, areas of night and morning dense fog will be possible near the coast this weekend and into early parts of the upcoming week. && .SHORT TERM (SAT-TUE)...29/853 PM. Slight warming trend occurred today across the interior with many locations climbing well into the 90s. Midlevel heights will continue to rise on Sunday and continue through the upcoming week, as an upper- level ridge builds westward from the south- central states. This will continue supporting a warming trend into the upcoming week. On Sunday, high temperatures are expected to have warmed to the 90s in most inland areas, 100-105 over the Antelope Valley, and the 70s near the coast. More significant warming is expected early in the upcoming week, with Tuesday high temperatures warming to 95-105 degrees in most inland areas, 105-110 over the Antelope Valley, and the middle 70s to the middle 80s near the coast. The Excessive Heat Watch for interior areas for the significant and long duration heatwave begins on Tuesday. This long duration heat wave will also bring an extended period of elevated to brief critical fire weather conditions across interior areas through much of next week (please see Fire Weather Planning Forecast discussion for more details on this upcoming fire weather threat). Local surface pressure gradients will remain moderately onshore. This overall pattern will maintain night and morning low clouds and fog across mostly coastal areas, scattering out and clearing in most areas during the afternoon. With the continued rising heights over the region, there will be a tendency for the marine layer to become increasingly shallow and favorable for dense fog development. Coastal areas and some coastal valleys will have the potential to experience dense fog tonight into Sunday morning, and again during subsequent overnight and morning hours. As of 830 pm this evening, already seeing a few coastal locations have visibilities lower to around 1 mile. Otherwise, dry conditions are expected into the upcoming week. Gusty southwest to northwest winds are expected each afternoon over interior areas, and strongest -- upwards of 35-45 mph -- over the Interstate-5 corridor as well as the Antelope Valley and nearby foothills. However, the issuance of Wind Advisories is currently unlikely. .LONG TERM (WED-SAT)...29/152 PM. Dangerously hot conditions are expected to continue over the region through the upcoming week, as an upper-level anticyclone builds offshore and expands eastward over California. Medium-range model guidance continues to suggest 500-mb heights rising to around 596-600 dam to the north of the area by late in the upcoming week. This should correspond to daily high temperatures up to 100 to 105 possible in many areas away from the coast, with highs upwards of 105 to 115 possible over interior valleys and foothills including the Antelope Valley. Warm overnight low temperatures will worsen the effects of extreme heat, with lows not falling below 80 degrees at some locations over interior valleys and nearby foothills. The Excessive Heat Watch continues for a large portion of the region away from the coast through late in the upcoming week, when temperatures could reach records at some locations. In addition, very warm to hot conditions will have the potential to bring significant heat impacts toward the coast, starting on Wednesday and continuing through the remainder of the upcoming week. This would occur as the marine layer becomes increasingly shallow and retreats toward the coast provided the rising heights aloft, which could also eventually limit the chances for night and morning dense fog. Heat headlines may need to be expanded to include a larger portion of Southern California in later forecasts. Present indications are that precipitation will be unlikely (below 20% chance) through late in the upcoming week. However, given how hot and strongly mixed the boundary layer will be over interior sections during latter parts of the week, any low- predictability monsoonal moisture influx south of the midlevel ridge axis could introduce chances for showers or thunderstorms over higher terrain. Chances are too low for mention in the forecast at this time, though this scenario will continue to be monitored. && .AVIATION...30/0128Z. At 0020Z at KLAX, the marine layer was 1000 feet deep. The top of the inversion was at 2400 feet with a temperature of 27 Celsius. High confidence in VFR conditions through Sunday at KPRB KBUR KVNY KWJF KPMD. High confidence in lower ceilings and visibility with less low cloud coverage tonight compared to last night. Low confidence in timing and which airports will get ceilings tonight into Sunday. Chances for ceilings: KSBP (50% LIFR) KSMX (80% LIFR) KSBA (60% LIFR) KOXR (80% LIFR) KCMA (60% LIFR) KSMO (40% LIFR 40% IFR) KLAX (40% LIFR 40% IFR) KLGB (40% LIFR 40% IFR). Cannot discount VLIFR anywhere, especially KSMX KSBA. KLAX...Based on satellite trends, have accelerated timing of cigs in the 01-02z time range. Overall, high confidence of in ceilings being at least IFR tonight/Sunday morning with a 40% chance of LIFR conditions. Cannot discount a few hours of VLIFR dense fog. High confidence in any southeast winds staying under 06 knots. KBUR...High confidence in VFR conditions through Sunday with a less than 10% chance of ceilings 10Z-16Z. High confidence in seasonal winds. && .MARINE...29/735 PM. Dense fog (with visibilities one nautical mile or less) will threaten all waters through at least Sunday. There is a 40 percent chance that the fog will clear later tonight over Santa Barbara and San Luis Obispo Counties as the northwest winds increase. Any fog that forms for the remainder of the week will likely be dense, but expecting the coverage to shrink a little each day. High confidence in northwest winds increasing quickly tonight into Sunday and lasting through Monday Night. For the offshore waters from the Central Coast to Point Conception, There is a 80% chance of Gales by Sunday afternoon and night, and a 30% chance on Monday. Otherwise, high confidence in at least Small Craft Advisory winds from the Central Coast to San Nicolas Island. There is a 20% chance of these winds pushing deep enough into the Santa Barbara Channel to need a Small Craft Advisory, but the more likely outcome is for those winds to stay confined to the far western portion. As a result of these winds, expect building choppy seas over most waters, even those areas that are not very windy. Moderate confidence for abnormally light winds Tuesday through Wednesday. Winds will likely increase steadily starting Thursday afternoon through Saturday, but the chance for any Gales during that period is very small. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Watch remains in effect from Tuesday morning through late Friday night for zones 38-88-343>345-353-376>379-381>383. (See LAXNPWLOX). PZ...Small Craft Advisory in effect from 2 PM Sunday to 6 AM PDT Monday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 2 PM PDT Sunday for zones 670-673. (See LAXMWWLOX). Gale Warning in effect from 2 PM Sunday to 6 AM PDT Monday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 2 PM Sunday to 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX). && $$ PUBLIC...Cohen/Gomberg AVIATION...Gomberg/RK MARINE...Kittell/Sirard SYNOPSIS...Cohen weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox