Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
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137 FXUS66 KLOX 291308 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 608 AM PDT Sat Jun 29 2024 .SYNOPSIS...29/450 AM. A general warming trend will establish across the area through next week as high pressure aloft strengthens over the region. Warm temperatures over the area this weekend will likely turn dangerously hot across the interior toward the middle of next week. Near record heat is possible between Independence Day and Saturday, especially across the mountains and desert. A hot air mass could linger into next weekend. && .SHORT TERM (TDY-MON)...29/458 AM. Low clouds and fog are well-entrenched across the coast and lower coastal valleys this morning as moderate onshore flow remains in place. Stronger onshore pressure gradients brought some cooling on Friday, which led to more cloud coverage across the area last night and into this morning. While the coastal areas will see temperatures closer to persistence today, a warming trend will develop outside the marine influence as 500 mb heights climb across the region through the weekend. Earlier AMDAR soundings from KLAX indicated the marine layer depth around 950 feet deep around midnight, which did agree well NAM BUFR time height sections. If the NAM BUFR time heights section played out as progged, the marine layer depth has likely deepened to close to 2000 feet deep at KLAX. This is partially due to the influence of weak troughing to the northwest of the area and the eddy circulation still intact across the southern California bight. Actually, several eddy vortices can be seen on satellite early this morning, including one into the Santa Barbara Channel. Clouds could struggle to clear from the beaches today, but with the high pressure building in, the marine layer depth will shrink and thin rapidly throughout the late morning hours. Outside of the marine intrusion, the air mass will heat up across the region. EPS, GEFS, and CMC ensemble members solutions suggest a steady warming trend taking shape through Sunday. Closer to the coast due to the persistent marine layer depth, the warming trend will be a bit more muted, with less warming likely taking place. With the marine layer turning more shallow through tonight and into Sunday morning, there is a moderate-to-high chance that any low clouds and fog could form dense fog across the coastal areas. High-resolution multi-model ensemble members suggest a 40-50 percent chance of dense fog developing along the Central Coast and into the Los Angeles County beaches by daybreak Sunday. By Monday, the upper-level ridge of high pressure over north Texas this morning will push a bit to the east and allow for a weak upper-level trough over the North Pacific to drop into the Pacific Northwest. This trough should bring slight height falls and an increase in onshore flow. As a result, low clouds and fog could become more pronounced on Monday or Monday night, and the warming trend should level off, or maybe see a degree or two of cooling across the area. .LONG TERM (TUE-FRI)...29/457 AM. High pressure aloft will quickly lift the trough out of the region and build into the region from the west. Strong ridging over the North Central Pacific Ocean will build into the state through Friday. While there is still quite a large spread in the model solutions over how warm it will get and the strength of the high, the forecast ensemble members favor a very warm to hot air mass on Tuesday turning much hotter by Friday. Temperatures break away from NBM values in the extended period to advertise near record heat between Independence Day and Saturday. Record heat is introduced for Friday in the latest forecast with forecast temperatures of 111 degrees at Paso Robles and 114 degrees at Palmdale and Lancaster, with daily record values at 110 and 113 degrees respectively. While the hottest temperatures and highest likelihood of record high temperatures will be for the interior portions of the area, it should be noted that Woodland Hills Pierce College has a lower record high for July 5th. The record high for Pierce College is 105 degrees on July 5th, bookended by a 112 degree record high on July 4th and a 116 degree record high on Saturday, July 6th. The forecast currently advertises a tie of the record high for July 5th, but there is a moderate chance that this record could be broken. With the near record high temperatures expected and very warm overnight low temperatures forecasted, an Excessive Heat Watch remains in effect for the interior portions of the area as dangerously hot weather could develop causing heat stress and a higher likelihood of heat illness for anyone planning outdoor activities. The forecast keeps some semblance of a low clouds field near the coast into late week, but there is a moderate chance that low clouds and fog could be very patchy in nature given the high pressure center location. If any monsoonal moisture sneaks in from the southeast, the low cloud field could become non-existent as the clouds aloft will play tricks on the marine inversion. The latest EPS ensemble precipitable water value means continue to trend higher in the latest runs with the potential for monsoonal moisture. EPS PWAT means now exceed above 1.00 inch between Wednesday and Thursday. There are handful solutions offering a higher spread into the weekend and into early next week. Any increase in cloud cover could put a damper of excessive heat developing, especially if a thick cloud shield develops and cuts into temperatures. Though unlikely at this time, very slight chance PoPs remain in the forecast for each afternoon and evening from Wednesday through Friday across the interior portions of the area. As the forecast ensembles are at the mercy of convective parameters working as advertised, it is a low confidence but high impact type scenario. Stay tuned at this could become a wrinkle in the forecast. && .AVIATION...29/1306Z. At 12Z at KLAX, the marine layer was 1700 feet deep. The top of the inversion was at 4000 feet with a temperature of 22 C. High confidence in VFR conditions for KPRB, KPMD, and KWJF, and fairly high confidence in VFR conds at KBUR and KVNY. Otherwise, low clouds were widespread in all coastal areas, with clouds also in the lower valleys. Conds were mostly LIFR to VLIFR, except IFR to locally very low MVFR on the L.A. County coast. Skies should clear by mid morning in the valleys and late morning on most of the coastal plain. Cigs could linger at some beaches into the afternoon, but most likely will not. Expect widespread low clouds and fog in most coastal areas tonight with generally LIFR to VLIFR conds expected. KLAX...Moderate confidence the 12Z TAF. There is a 30% chance that IFR conds will not rise into the MVFR category this morning. There is a 20% chance that cigs will not scatter out until 19Z-20Z. There is a 20% chance that cigs will not arrive tonight until at least 11Z. KBUR...High confidence in the 12Z TAF with VFR conditions thru the period. least 11Z. There is a 10% chance of IFR ceilings from 14Z-16Z this morning. && .MARINE...29/552 AM. Areas of dense fog (with visibilities one nautical mile or less) will likely affect a good portion of the coastal waters this morning, possibly lingering into the afternoon. Dense fog is a good possibilty again late tonight and Sunday morning. In the outer waters, high confidence that Small Craft Advisory (SCA) level NW winds will spread from north to south across the area tonight, beginning into the northern zone (PZZ670) by mid evening. SCA level winds and seas will continue thru at least late Mon night in most of the outer waters. There is a 40% chance of Gale Force winds in the northern two zones (PZZ670/673) Sun afternoon thru late Sun night, and a 20% chance in the southern zone (PZZ676). There is a 20% chance of gales in the northern two zones Mon afternoon/eve. Mostly light winds are expected Tue thru Wed night, though seas could be close to SCA levels Tue. In the inner waters N of Pt. Sal, SCA conds are likely (70% chance) during the afternoon/eve hours Sun/Mon. Seas may stay at or above SCA levels Sun night/Mon morning when winds drop below SCA levels. Winds are expected to be rather light Tue thru Wed night. In the inner water S of Pt. Conception, there is a 60% chance of SCA level winds across western portions of the Santa Barbara Channel Sun evening, and a 30-40% chance late Mon afternoon/eve. Otherwise, SCA conds are not expected thru Wed night. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Watch 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 9 PM this evening to 3 PM PDT Sunday for zone 670. (See LAXMWWLOX). Gale Watch in effect from Sunday afternoon through late Sunday night for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM to 3 PM PDT Sunday for zone 673. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM Sunday to 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX). && $$ PUBLIC...Hall AVIATION...DB MARINE...DB SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox