Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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209 FXUS66 KLOX 021631 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 931 AM PDT Tue Jul 2 2024 .SYNOPSIS...02/913 AM. A significant heatwave will impact the region this week through early next week, with dangerously hot temperatures across much of the area. High temperatures by mid to late week are expected to reach 95 to 105 degrees in many areas away from the coast, with highs upwards of 105 to 115 over interior valleys and foothills, including the Antelope Valley. Very warm to hot conditions could extend closer to the coast by late this week. Patchy night to morning dense fog will be possible near the coast tonight as well as Wednesday and Thursday mornings. && .SHORT TERM (TDY-THU)...02/931 AM. ***UPDATE*** No changes this morning and likely minimal changes with the afternoon update as well. Forecast remains in tact with a significant heat wave developing across our interior areas today and spreading into the valleys and to a lesser degree for the inland portions of the coastal areas Wednesday and Thursday. Models still indicating a very strong upper high over the eastern Pacific drifting slowly towards northern California and encompassing the entire state by around Thursday and peaking in strength Friday through the weekend. Of particular interest and concern is the bubble of very hot air coupled with increasing northerly flow across the Santa Ynez Range Friday evening. The 12z NAM shows 950mb temps of 40c at that time and coupled with adiabatic processes could be even warmer at the surface. This is one area where additional heat hazards, either a heat advisory or warning may be needed. ***From Previous Discussion*** The eddy picked up a little more than expected and low clouds have penetrated a little deeper into the vlys than was expected. The increase in marine layer depth has eliminated the threat of dense fog. Other than the more robust low cloud coverage the forecast is on track with slight warming today followed by more aggressive warming Wed and Thu. This heatwave will be generated by a large and warm upper high that will nose into the state from the west. Hgts over KLAX will rise from 590 dam this morning to a near record 597 dam (since 1948 the highest 500 mb hgt over KLAX was 598 dam). At the same time the offshore flow will weaken. The impressive hgts will smoosh the marine layer down until it will only affect the near shore area. Look for 2 to 4 degrees of warming away from the coast today with the coastal areas not showing much change. On Wednesday there will be 3 to 6 degrees of warming everywhere followed 4 to 8 degrees of warming for the csts and vlys Thursday as the marine layer retreats to the beaches. On Thursday the inland coastal areas will be 4 to 8 locally 10 degrees above normal while the vlys and interior will be 10 to 15 degrees over normal. In addition to the highs overnight lows will be uncomfortably warm in the warm inversion zone (elevations ~800 to 1600 ft) where lows will only reach the lowers 80s or upper 70s. Heat warnings already cover the interior and most of the vlys (and last until Monday) Heat advisories were added for the San Gabriel Vly for Wed to Sun and the interior coastal sections for Thu to Sun. Please see the product LAXNPWLOX for all the details and precautions. Winds through the short term should be typical onshore winds each afternoon to evening period, affecting the interior passes and canyons, and the Antelope Valley. .LONG TERM (FRI-MON)...02/303 AM. Friday will be the warmest day as onshore flow reaches a minimum and hgts remain near 597 dam. Look for another 2 to 4 degrees of warming with max temps 110-115 across the interior, 100 to 105 in the vlys, 90s across the interior coastal sections and 80s at the beaches. These max temps are 6 to 12 degrees above normal for the csts and 12 to 18 degrees over normals for the vlys and interior. The very warm overnight lows will continue as well. Sundowner winds are possible across the SBA south coast Thu and Fri evenings and overnight and if these do occur very warm conditions will rapidly develop in that area with unusual daily highs occurs during the evening. Only minimal cooling is forecast over the weekend and all of the heat warnings and advisories will continue through the period. A steady increase in onshore flow will bring cooling first to the csts and then into the vlys. The interior will not see much relief at all as hgts remain very high. Long range guidance does not show the upper high breaking down much at all next week and this extended heat wave may push deep into next week (esp inland) The combination of these very hot temperatures, areas of low humidities and possible sundowner winds will lead to fire weather risks. Please see the fire weather discussion below for all the details. && .AVIATION...02/1624Z. At 16Z at KLAX, the marine layer was 1700 feet deep. The top of the inversion was at 3400 feet with a temperature of 24 Celsius. High confidence in CAVU TAFs for KPRB, KPMD and KWJF. Lower confidence in remainder of TAFs. Where low cigs continue this morning, VFR transition could be 2-3 hours off, especially KSBA, KOXR, KSMO and KLAX and there is a 10-20% chance of brief to no clearing today. There will be a return to MVFR/IFR cigs/vsbys near the coast again tonight into Wednesday morning, with onset timing +/- 3 hours of current forecasts. KLAX...Moderate confidence in TAF. There is a 10-20 percent chance of no clearing today. No significant easterly wind component is expected. KBUR...Moderate to high confidence in TAF. && .MARINE...02/311 AM. For the Outer Waters, through Thursday, high confidence in winds and seas remaining below SCA levels. For Friday and Saturday, there is a 20-30% chance of SCA level winds. For the Inner Waters north of Point Sal, through Saturday, high confidence in winds and seas remaining below SCA levels. For the Inner Waters south of Point Conception, high confidence in current forecast. Through Saturday, winds and seas will remain below SCA levels. Patchy dense fog (with visibilities one nautical mile or less) will continue to impact the coastal waters through the week. The areal coverage of the dense fog will likely decrease each day, especially after Wednesday or Thursday. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning remains in effect until 6 PM PDT Monday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX). Excessive Heat Warning remains in effect from 11 AM Wednesday to 6 PM PDT Monday for zones 88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX). Heat Advisory in effect from 11 AM Thursday to 6 PM PDT Sunday for zones 341-347-355-368. (See LAXNPWLOX). Heat Advisory in effect from 11 AM Wednesday to 6 PM PDT Sunday for zone 548. (See LAXNPWLOX). PZ...NONE. && $$ PUBLIC...MW/Rorke AVIATION...Cohen/Munroe MARINE...Munroe/Phillips/RAT SYNOPSIS...Cohen/Smith/MW weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox