Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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102 FXUS66 KLOX 011002 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 302 AM PDT Mon Jul 1 2024 .SYNOPSIS...30/219 PM. A significant heatwave will impact a large part of the area this week and continue into next weekend. Temperatures will become dangerously hot 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. Also, by late week, very warm to hot conditions could extend closer to the coast. Patchy night and morning dense fog will be possible near the coast early this week. && .SHORT TERM (TDY-WED)...01/244 AM. The marine layer is 900 ft deep but is slowly rising as an eddy spins and lifts the marine layer. By dawn low clouds should cover almost all of the coasts and will extend into a few vlys notably the San Gabriel and eastern San fernando. A weak trof will pass over the area today will will further lift the clouds. Low clouds will slowly dissipate this morning but with an 8 mb onshore push to the east in the afternoon it is likely that a few west facing beaches will not clear. The lower hgts from the trof and the deeper marine layer will team up to knock 2 to 4 degrees off the max temps. The coastal areas will end up a few degrees blo normal while the rest of the area will see near normal temps. After today the forecast will be all about the heat. The heat wave will start Tuesday as a large and warm E Pac high begins to nose into the state from the west. There will be marine layer clouds across the coasts in the morning but there will be weaker onshore flow so clearing should be a little faster and more beaches will see sunshine. Max temps will rise 1 to 2 degrees across the coasts and vlys except for the Central Coast where even weaker onshore flow will allow for a 3 to 5 degree warm up. The warm up will begin in earnest on Wednesday as the upper high pushes further into the state and hgts rise to 595 dam over LA county and 596 dam over the Central Coast. At the same time the onshore flow will lessen which will lead to a later arriving and weaker sea breeze. The marine layer will be squashed to under 1000 feet and likely lower to near 600 ft. This will lead to low clouds only covering the near shore area in the morning. The capping inversion will be very strong and this may prevent some beaches from clearing. Max temps will rocket up 5 to 10 degrees everywhere. There will many 80 degree reading across the interior coast, lots of 90s and some 100 to 101 degree readings in the vlys. The interior and lower mtn elevations will see max temps ranging from 102 to 106 degrees. The Antelope Vly will have dangerous heat with highs of 108 to 112 degrees. The Excessive Heat Warning for interior areas starts on Tuesday which may be a day early and the day shift will have to consider pushing the start date back a day. There is no doubt about the need for Warnings across the interior on Wednesday. In addition to the warnings, an Excessive Heat Watch has is also in effect from the San Fernando Valley through the Santa Monicas, Calabasas, and Agoura Hills, to the central Ventura County valleys and through the Santa Ynez Range and Santa Lucia Range. Overnight lows will have to monitored as the areas in the warmest portion of the inversion (likely 800 to 1500 ft elevations) may not see much cooling relief at all in the overnight hours. n addition, gusty west to northwest winds are expected each afternoon over most of the interior areas. The strongest gusts (35-45 mph) will occur over the I-5 corridor and the western Antelope Valley/foothills. These gusts will come in just under wind advisories criteria. .LONG TERM (THU-SUN)...01/302 AM. The heat wave will persist through the xtnd period and into early next week. The upper high will move directly atop of the state and Srn CA will have hgts near 596 dam overhead through the entire period. The sfc gradients weaken considerably on Fri and Saturday and these will be the warmest two days with only a minimal amount of marine layer clouds or marine layer influence. Look for 2 to 4 degrees of warming each day Thu and Fri and just a little cooling over the weekend. The Excessive Heat Warnings and Watches will continue all the way through the weekend and into early Monday morning, July 8 with max temps of 95-105 degrees in many areas away from the coast, with highs upwards of 105-115 over interior valleys and foothills including the Antelope Valley. With max temps 10 to 20 degrees above normal, Major to Extreme heat risk is likely through the weekend, especially Friday. Overnight low temperatures will be well above normal in the inversion zone with lows remaining above 80 degrees at some locations over interior valleys and nearby foothills. These warm lows will worsen the effects of extreme heat. Even though they are not included in the watch the interior coastal sections may well need Heat Advisories during the period as the marine layer shrinks until it is too shallow to provide much relief to the portion of the coast not in the near shore area. One last area of concern is the SBA south coast where Sundowners are possible Thursday and Friday nights. Warming downsloping sundowner winds could easily bring near 100 degree temperatures to the SBA south coast including the city of SBA during the early evening hours. 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...01/0625Z. At 06Z at KLAX, the marine layer was 600 feet deep. The top of the inversion was at 2300 feet with a temperature of 26 Celsius. High confidence in VFR conditions for for KPRB, KWJF and KPMD through at least Monday. Moderate confidence in all airports that get ceilings seeing LIFR conditions at times, low confidence on coverage and timing. VLIFR dense FG possible anywhere, especially before 12Z. There is a 30-40 percent chance of improving flight categories after 10Z due to an eddy focused across KLAX, KSMO, KLGB. For KBUR and KVNY there is a 10-20 percent chance that the eddy is strong enough for at least brief LIFR/VLIFR cigs/vsbys in the 10-15Z time frame. KLAX...Low confidence in TAF with a moderate to strong eddy providing a 30-40 percent chance of improving flight category after 10Z. There is a 30 percent chance of a brief return to VFR conds between 07Z-10Z. Return to VFR later this morning may be off by 3 hours. High confidence in any easterly wind component staying well below 06 knots. Note that the TAF will reflect vsby on the ground, not at the tall tower at 300 ft agl. KBUR...Moderate confidence in VFR conditions with a 10-20 percent chance of LIFR cigs/vsbys between 10-15Z. && .MARINE...01/235 AM. For the Outer Waters, moderate to high confidence in current forecast. Through Monday night, high confidence in Small Craft Advisory (SCA) level winds from San Nicolas Island northward. For the waters north of Point Conception (PZZ670/673), there is a 50-60% chance of Gale force winds through early this morning and 30-40% chance of Gale force winds Monday afternoon and Monday night. The GALE WARNING for PZZ670/673 has been extended through 9 am this morning. For Tuesday through Friday, high confidence in winds and seas remaining below SCA levels. For the Inner Waters north of Point Sal, moderate confidence in current forecast. There is a 40-60% chance of SCA level winds through this evening. For Tuesday through Friday, high confidence in winds and seas remaining below SCA levels. For the Inner Waters south of Point Conception, there is a 30% chance of SCA level winds this afternoon/evening but likely will stay very localized. Otherwise, high confidence in winds and seas remaining below SCA levels through Friday across the Inner Waters south of Point Conception. 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. && .FIRE WEATHER...30/429 PM. Elevated fire weather conditions will continue across the interior valleys, mountains, and deserts through Monday due to hot temperatures, low humidities, and locally gusty onshore winds. Beginning on Tuesday, and continuing into next weekend, high pressure will build into the region from the Eastern Pacific. This will likely bring a significant and long duration heat wave away from the coast from Tuesday through next weekend. High temperatures between 100 and 110 degrees will be common across the interior during this period, with temperatures potentially rising to between 110 and 115 degrees across the Antelope Valley and San Luis Obispo County interior valleys during the peak of the heat Thursday through Saturday. Overnight lows will also remain quite warm, adding to the potential for dangerous heat mid to late week. Widespread humidity values between 7 and 15 percent will likely occur across the interior during this period, along with poor humidity recoveries, especially in the mountains, foothills, and Antelope Valley. Typical gusty onshore winds are expected across interior sections in the afternoon and evening hours, with gusts of 20 to 35 mph common. There is also the potential for gusty sundowner/I5 corridor winds late Thursday into Friday night which could bring hot and dry conditions into portions of southern Santa Barbara county. Given the very hot temperatures, low relative humidity, and locally gusty winds, an extended period of elevated to brief critical fire weather conditions are likely from Tuesday through Sunday for valley, foothill, mountain, and desert locations. Elevated to critical fire weather conditions may expand into southern Santa Barbara county if the sundowner winds develop late Thursday into Friday night. The hot and unstable conditions will also increase the threat of large vertical plume growth for any fires that develop across the interior. The very hot and dry conditions will also cause a significant drop in both live and dead fuel moisture levels this week. These drying fuels combined with the expected fire weather conditions and increased outdoor activities associated with the 4th of July will cause the large fire threat to become high for areas away from the coast Tuesday through next weekend. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning remains in effect from 11 AM Tuesday to 5 AM PDT Monday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX). Excessive Heat Watch remains in effect from Wednesday morning through late Sunday night for zones 88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 9 PM PDT this evening for zone 645. (See LAXMWWLOX). Gale Warning in effect until 9 AM PDT this morning for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX). && $$ PUBLIC...Rorke AVIATION...Munroe MARINE...RM/RAT/RK FIRE...Gomberg SYNOPSIS...Cohen weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox