Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

454 am PDT Mon apr 24 2017

Synopsis

An upper trough moving through the Pacific Northwest will bring cooler weather to the region today with gusty northwest to north winds in some areas. Persistently sharp north to south pressure gradients will keep breezy to locally windy conditions across much of the region through at least Thursday. Temperatures will generally be above normal in most areas Tuesday through Friday, then well above normal over the weekend.

Short Term

(tdy-Wed)

An eddy circulation across the inner waters has caused the marine layer to deepen to over 1500 feet, and an organized area of low clouds has overspread coastal sections of L.A. County and the San Gabriel Valley. Clouds were beginning to spill into the San Fernando Valley, and may spread into VTU County from the east by daybreak. Low clouds have also developed on the Central Coast and in the Santa Ynez Valley. Otherwise, there was a fair amount of high cloudiness drifting across the region this morning. Expect low clouds to break up by late morning or around noon, then it should be partly cloudy across the region. Max temps should be down a few more degrees in most areas, down to near normal levels in most areas.

Main story will be the winds. Good n-s low level gradients, and decent upper support with good NW winds at 850 mb and subsidence should continue to bring advisory level winds to the Interstate-5 Corridor, southern Santa Barbara County through and below passes and canyons, and the Antelope Valley today and tonight. Expect advisory level northwest winds to develop on the Central Coast this afternoon and evening.

An upper low will drop southeastward through the Pac NW today and tonight, then into Utah on Tuesday. Models show some decent upslope moisture from the northerly flow pushing into the north facing mountain slopes tonight and Tue morning, and there will be plenty of clouds and even a slight chance of showers. Low cloud forecast for tonight and Tue morning is difficult. The WRF shows low level nly flow wiping out the clouds in coastal and valley areas south of Pt Conception, with stratus developing late tonight and early Tue on the Central Coast as low level northerly flow pushes against the northern slopes of the Santa Ynez Range.

Good northwesterly flow aloft and decent n-s low level gradients should bring continue gusty northwest to north winds to the same areas tonight through Tuesday night, so advisories in place through late Tue night look good. Wind advisories will likely be needed for the Central Coast Tue afternoon, and possibly for coastal sections of L.A. and VTU Counties. Slight rises in heights and thicknesses and less in the way of low clouds should lead to a couple of degrees of warming on Tue, especially in coastal and valley areas.

Looks like less in the way of low clouds Tue night/Wed. Max temps should rise a few more degrees in most areas on Wed as thicknesses and heights cont to rise.

Long Term

(Thu-Sun)

An upper low will drop into Idaho and Montana Wed night and Thu, then into Utah on Fri. This will cause northwesterly flow aloft to increase across the region Thu and Fri, and with continued sharp n-s gradients, expect gusty northwest to north winds to continue at times through Fri. Low level moisture on northern mountain slopes could cause a few showers again late Wed night/Thu morning, but have held off pops for now. There will be a few degrees in most areas Thu, with additional cooling across the mtns and Antelope Valley on Fri.

Height and thicknesses will rise over the weekend as an upper ridge amplifies along the West Coast. Low level flow will turn more northeasterly by Sat, and remain offshore, though weakly on Sunday. Max temps should jump Sat, especially west of the mountains, with well above normal temps expected in most coastal and valley areas next weekend.

Aviation

24/1200z,

At 11Z, the marine inversion at KLAX was based at 2100 feet. The top of the inversion was around 3000 feet with a temp of 15C.

Expect MVFR conds across LA County coast and valleys to the coastal slopes. Also some MVFR stratus was developing around Santa Ynez Valley and there is a 50% chance for MVFR stratus across portions of the Central Coast through 16z. Also 50% chance for some patchy MVFR stratus across Ventura Coast and Valleys after 13z to 18z this morning.

There will be areas of gusty NW winds through the pd across the I5 Corridor, southern SBA County, the Antelope Valley and on the Central Coast. Expect some LLWS and mdt UDDF through and below passes and canyons, especially near KSBA.

KLAX, High confidence in the 12Z TAF through 17z with MVFR cigs. There is a 30-40% chance that conds will persist into early this afternoon. Gusty northerly winds should keep any stratus from developing this evening into Tue morning.

KBUR, Moderate confidence in 12Z TAF with MVFR conds thru 16-17z this morning. Then VFR conds through Tue morning.

Marine

24/300 AM,

For the Outer Waters, high confidence in current forecast. Strong northwest winds are anticipated to continue through the week. Currently, a Gale Warning is in effect through late Tuesday night. 60-70% chance that Gale force winds will likely continue through Friday.

For the Inner Waters, moderate to high confidence in current forecast. For the waters north of Point Sal, strong Small Craft Advisory (SCA) level winds are expected each afternoon/evening through Friday with a 30% chance of Gale force winds developing Tuesday through Friday. For the waters south of Point Conception, SCA level winds are expected each afternoon and evening through Friday with the strongest winds across the western Santa Barbara Channel. Expect local gusts to 35 knots across the western portions of the inner waters. For now have kept in strong SCA for the inner waters. But there is a 60% for local gusts to 35 kt late this afternoon through late this evening. And once again Tuesday afternoon into the late evening hours. There will continue to be a 50% chance of Gale force winds across the far western portion Tuesday through Friday across western sections. A 30% for widespread gale winds for the same time frame.

Due to strong winds throughout the waters, seas will be very choppy this week, making for hazardous boating conditions through the week.

Watches, Warnings, Advisories

Ca, High Surf Advisory in effect until 10 PM PDT this evening for zones 34-35-40-41-87. (See LAXCFWLOX). Wind Advisory in effect until 3 AM PDT Tuesday for zones 34-35. (See LAXNPWLOX). Wind Advisory in effect until 3 AM PDT Wednesday for zones 39-52>54-59. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Wednesday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 1 PM this afternoon to 3 AM PDT Wednesday for zones 650-655. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Wednesday for zones 670-673-676. (See LAXMWWLOX).

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