749 FXUS66 KLOX 150418 AFDLOX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 918 PM PDT Sat Oct 14 2017 .SYNOPSIS... Offshore flow beneath high pressure aloft will bring warm temperatures, gusty winds, and fire danger to portions of the area through the weekend. The high pressure ridge should weaken by midweek for a cool down, then a low pressure system will approach on Thursday for below normal temperatures and possible precipitation into Saturday. && .SHORT TERM...(SAT-TUE) Offshore flow continues to develop tonight as surface pressure gradients are trending more strongly offshore. KLAX-KDAG surface pressure gradient trends are hovering near -6 mb offshore and KLAX-KTPH to near -8 mb offshore. Linear extrapolation should push KLAX-KDAG surface pressure gradients in excess of -7 mb by Sunday morning. Winds, slower to develop earlier today, should start to increase over the next couple of hours and gradients tighten and better upper-level support arrives. No changes have been to the current Wind Advisories in effect at this time. With offshore flow developing, a warming trend will continue for Sunday. Temperatures have been nudged a little high for Ventura and Los Angeles Counties for Sunday. KLAX AMDAR sounding have a thin but strong inversion, which should get wiped out over the coming hours as offshore develops. In wind-sheltered locations, clear skies and calm winds will allow for radiative cooling processes to be a bit more efficient tonight. A Frost Advisory has added for late tonight and into Sunday morning for the Antelope Valley and San Luis Obispo County Interior Valleys. *** FROM PREVIOUS DISCUSSION *** Offshore gradients weaken quite a bit Monday and Tuesday but still remain offshore with a very warm air mass in place and the high pressure ridge aloft hanging tough across So Cal. So temps will remain well above normal with just some minimal cooling near the coast. Warmer valleys will threaten triple digits but most areas in the 90s. .LONG TERM...(WED-SAT) Weak offshore flow now expected to remain in place through Wednesday and still pretty decent ridging aloft so again only minimal cooling Wednesday with highs still 3-6 degrees above normal. After Wednesday forecast confidence drops quite a bit as models have been really bouncing around with the strength and timing of the next trough hitting the west coast as well as how much moisture it pulls in from the southwest. It looks like we should see at least one more dry day Thursday but cooler as gradients trend strongly onshore. And likely some marine lyr clouds increasing as well. Both the GFS and ECMWF 12z solutions show the trough axis moving onshore over Nrn CA around 18z Friday and passing through the rest of the state Friday afternoon and evening which is a good 12 hours delayed from earlier runs. Today's solutions are also noticeably less moist and don't drop quite as far south as previous runs showed and resulting precip forecasts are lower as well. In fact they are basically dry for most of LA/Ventura counties. But these solutions have varied considerably run to run and and it still looks like some chance of rain late next week, though just not confident on timing and strength. && .AVIATION...15/0137Z. At 00Z, the marine layer depth was around 600 feet deep at KLAX. The top of the inversion was around 1200 feet with a temperature near 27 degrees Celsius. Moderate-to-high confidence in VFR conditions throughout the period. Moderate-to-strong wind shear and turbulence is possible at all terminals through 16Z. KLAX...VFR conditions are expected throughout the period, except for a 30 percent chance of MVFR conditions between 12Z and 16Z. KBUR...VFR conditions are expected throughout the period. There is a 30 percent chance of moderate wind shear and turbulence between 02Z and 12Z. && .MARINE...14/800 PM. No issues with wind or seas expected over the outer waters through Tuesday, except local gusts to 25 kt between San Nicolas Island and Santa Cruz Island late tonight through Sunday morning. Increasing NW winds with possible SCA possible as a frontal system approaches Wednesday into Thursday. Gusty northeast winds across the nearshore waters will develop this evening and reach Small Craft Advisory (SCA) levels south of Point Conception, mainly from Ventura to Santa Monica. The winds will diminish Sunday afternoon. There is a 20% chance that northeast wind gusts to 25 kt and short period northeast swell of 2 to 4 feet will affect Avalon Harbor Sunday morning. && .FIRE WEATHER...14/205 PM. Overall, everything still on track with regard to Red Flag conditions across Ventura and Los Angeles counties. Offshore winds are expected to increase this evening and overnight as the surface pressure gradient increases. So, wind gusts between 35 and 55 MPH will be likely across Ventura and Los Angeles county tonight and Sunday morning. The winds will diminish gradually Sunday afternoon. As for relative humidity, very dry air will remain in place over the area through Sunday. So, widespread and long-duration critical fire weather conditions are expected and the Red Flag Warning will remain in effect until 600 PM Sunday for Ventura and Los Angeles counties (except for the Antelope Valley). For Santa Barbara and San Luis Obispo counties, the offshore winds will be much weaker and more localized through Sunday. However, the air mass will still be as warm and dry. So, elevated fire weather conditions can be expected across these areas through Sunday evening. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Frost Advisory in effect from 2 AM to 9 AM PDT Sunday for zones 37-59. (See LAXNPWLOX). Wind Advisory in effect until 2 PM PDT Sunday for zones 40-41-44>46-53-54-88-547. (See LAXNPWLOX). Red Flag Warning in effect until 6 PM PDT Sunday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX). PZ...Small Craft Advisory in effect until 2 PM PDT Sunday for zones 650-655. (See LAXMWWLOX). && .HAZARD POTENTIAL OUTLOOK...(TUE-SAT) Elevated surf and strong rip currents are possible at area beaches Tuesday through Thursday. && $$ PUBLIC...Hall/MW AVIATION...Hall MARINE...Smith FIRE WEATHER...Thompson SYNOPSIS...STu/Hall weather.gov/losangeles