Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000 FXUS66 KLOX 250540 AFDLOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 1030 PM PDT SAT SEP 24 2016 .SYNOPSIS... Gusty Santa Ana winds with hot and dry temperatures will peak Sunday and Monday. An upper level trough of low pressure will help to increase the onshore flow and bring a gradual cooling trend to the area Tuesday through the end of the week. && .SHORT TERM...(SAT-TUE) A 597 dm area of high pressure that is currently 700 miles west of Los Angeles is continuing its slow march toward California. Meanwhile high pressure over the surface of Idaho is building and sliding south...still on track to arrive in the Utah/Nevada area tomorrow. The hot and windy weather story we have been advertising for Sunday and Monday remains on target. Winds are mostly behaving themselves at this point with a few spots gusting to around 20 mph. These winds should start picking up after midnight tonight over Los Angeles and Ventura Counties...first for the mountains...then into the valleys early Sunday morning...then into the coastal sections by around 9 am. Peak gusts between 35 and 55 mph are still the target...and the current wind advisories look good (though the start time is on the early side). Temperatures will be on the rise on the coastal side of the mountains, and while the current forecast may be a bit on the hot side, the general idea is hard to argue with. High temperatures between 92 and 102 will be common, but records are quite high and look safe. Regardless, heat-related illnesses will be a serious concern and sensitive populations (like outdoor workers, the elderly, and children) should get prepared now. Fire weather concerns abound to no surprise and the current suite of Red Flag Warnings look good. Looking further out, computer projections are looking more favorable for convection on Tuesday as a low currently forming over Arizona wobbles up into southern California. If the current solutions hold, we will probably need to mention thunderstorms in the forecast for at least the Los Angeles and Ventura County mountains and deserts. .LONG TERM...(WED-SAT) Latest guidance was reasonably consistent with previous runs through the period and dry conditions will persist with a cooling trend. Temperatures near the coast will likely be 5-10 degrees below normal within a marine layer while above normal temperatures persist in the interior under clear skies but the interior areas are expected to trend cooler by 2-4 degrees each day through the period. Otherwise the remnant tropical low centered east of the area will shift east as a mid latitude trough advances over the Eastern Pacific Wednesday. The mid latitude trough is expected to amplify while approaching and height/thickness will lower/decrease over the area through the period. && .AVIATION... 25/0530Z At 0500Z at KLAX, there was no marine layer. There was a sfc based inversion with a top of 1600 feet and temperature of 28 degrees C. Very high confidence in CAVU TAFs. There will be some LLWS at all terminals through 18Z. KLAX...Very high confidence in CAVU TAF. There is a 40 percent chc that the east winds will not be as strong as fcst. KBUR...Very high confidence in CAVU TAF. && .MARINE...24/800 PM. Easterly winds will flirt with Small Craft Advisory (SCA) thresholds from Ventura to Malibu Sunday and Monday from 8am to 2pm. 40 percent chance of east winds pushing out through the Channel Islands to Point Conception. 20 percent chance of the east winds reaching Avalon. Despite these east winds...stiff westerly breezes are likely near the coast each afternoon. There is a chance for 10 to 20 knot southeast winds Tuesday morning from Point Conception to San Onofre including the San Pedro and Santa Barbara Channels. Dense fog will be possible after Tuesday off the Central Coast and after Wednesday elsewhere. && .FIRE WEATHER...24/500 PM. An extended period of critical Red Flag fire weather conditions across much of Los Angeles and Ventura counties through Monday, with elevated fire danger across remaining areas. Widespread minimum relative humidities so far today have been between 8 and 15 percent away from the coast. North to northeast winds are currently gusting 20 to 35 mph across the Los Angeles and Ventura County Mountains and Valleys with similar winds expected through this evening. The Santa Ana winds are then expected to increase in areal coverage and intensity late tonight and especially Sunday, when the offshore winds are expected to spread all the way to the coast from Ventura to Malibu with peak gusts ranging up to 55 mph across the mountains and up to 45 mph closer to the coast. LAX- Daggett gradient expected to peak around -5 mb on Sunday morning, along with better upper level wind support. The most critical fire weather conditions are expected on Sunday across Southern California due to the stronger Santa Ana winds, widespread triple digit temperatures, and widespread single digit humidities. This type of critical fire weather scenario combined with the exceptionally dry fuels would bring the potential for very rapid fire spread along with extreme fire behavior (including long range spotting) for any new fire ignitions. In addition, very warm temperatures and poor humidities can be expected at night across the foothills and wind prone areas. Gusty Santa Ana winds will likely continue Sunday night into Monday but wind gusts are not expected to be quite as strong and will be more easterly in nature. Continued very hot and dry conditions on Monday will likely maintain the critical fire weather conditions. By Tuesday there is a 10 to 15 percent chance of thunderstorms across Los Angeles and Ventura counties in response to mid level moisture possibly working its way into the area from the southeast. Otherwise, gradual cooling is expected to continue through the middle to end of next week with a slow increase in marine layer coverage to the west of the mountains. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect from 6 AM to 6 PM PDT Sunday For zones 40-41. (See LAXNPWLOX). Wind Advisory in effect from midnight tonight to 3 PM PDT Monday For zones 44>46-53-54-547. (See LAXNPWLOX). Red Flag Warning in effect from midnight tonight to 3 PM PDT Monday For zones 240-241. (See LAXRFWLOX). Red Flag Warning in effect until 3 PM PDT Monday For zones 244>246-253-254. (See LAXRFWLOX). PZ...NONE. && $$ PUBLIC...14/30 FIRE...Munroe AVIATION...ASR MARINE...Kittell SYNOPSIS...Sirard is the U.S. government's official web portal to all federal, state and local government web resources and services.