Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

123 pm PDT Fri aug 17 2018


17/1146 AM.

Temperatures will begin increasing and humidity decreasing by mid period as an area of high pressure centers over California and surpresses both onshore and monsoon flows. Temperatures will vary between near normal this weekend and above normal next week.

Short Term

(tdy-Mon), 17/117 PM.

Definitely a slower day convection-wise but still getting some TCU across the eastern San Gab mtns. Would not be surprised to see some sprinkles or showers near the Wrightwood/Big Pines area through the evening but the earlier referenced capping inversion and overall weaker instability should limit vertical development.

Otherwise, a pretty quiet pattern overall with just minor day to day changes. Temps began a slow climb yesterday that will more or less continue through the weekend as high pressure expands west to cover most of California. Models do indicate a 1-2mb onshore trend Saturday that could actually lead to very slight cooling, mainly west of the mountains but otherwise a pretty static pattern through early next week. The marine layer is expected to slowly decrease in depth and by Sun should be completely out of the valleys. Warmest valley areas will get close to triple digits Sunday with coastal areas mostly in the 70s and 80s (cooler along the Central Coast). Perhaps a little cooler Monday as a trough develops along the Pac NW coast and forces the ridge to pull back to the east.

Long Term

(Tue-Fri), 17/122 PM.

The Monday trough will linger into Tuesday then lift out Wed/Thu. As this happens onshore gradients will weaken and high pressure will rebuild from the east again. This will lead to a 2-5 degree warm up and push temps to their warmest in this seven day period with valley highs up to 105 and inland coastal areas into the lower 90s. Another trough hitting WA/OR later in the week will again push the ridge east and lead to cooling area-wide, but still a few degrees above normal at least. Models keep the monsoon moisture east of LA County so for now no threat of convection through next week.



At 1727Z at KLAX, the marine inversion was around 1700 ft deep. The top of the inversion was around 3400 feet with a temperature near 24 degrees Celsius.

Moderate confidence overall in the 18Z TAFs due to the timing and extent of low clouds at all coastal and adjacent vly airfields during the period. Low clouds with LIFR/IFR/MVFR cigs are expected to move into these airfields generally from around 04Z at KSMO and KLAX to around 11Z at KSBA. The low clouds are forecast to dissipate by late Sat morning, except should linger until 18Z Sat morning for KSBA and KOXR. The timing of the onset and dissipation of the low clouds may be off +/- one to three hours. Otherwise, hi confidence in VFR conditions at the rest of the airfields thru Sat morning.

KLAX, Moderate confidence overall in the 18Z TAF. Low clouds with MVFR cigs are expected at the airfield from about 04Z-19Z Sat. Otherwise, VFR conditions can be expected thru Sat afternoon. The timing of the onset and dissipation of the low clouds may be off +/- an hour or two. There is also a 30% chance of MVFR cigs at times late this afternoon with the seabreeze.

KBUR, Moderate confidence overall in the 18Z TAF. Low clouds with MVFR cigs are expected at the airfield from about 09Z-1630Z Sat. Otherwise, VFR conditions can be expected thru late Sat morning. The timing of the onset and dissipation of the low clouds may be off +/- an hour or two.


17/1254 PM.

For the Outer Waters, there is a 20%-30% chance of Small Craft Advisory (SCA) level winds in the central outer waters this evening and Sat evening. There is also a 30%-40% chance of SCA wind gusts Sun night and Wed for PZZ673 and PZZ676. Otherwise, conditions will remain below SCA level through Wed.

For the Inner Waters, Conditions will remain below SCA level through Wed.

There is a 30% chance of patchy dense fog in the overnight and morning hours in portions of the coastal waters through Sun.

Increased south swell will result in hazardous conditions for mariners through Sat evening, particularly near the surf zone.


17/1248 PM.

A southerly swell will keep surf heights elevated across the region through Saturday, which will also bring strong rip currents and sneaker waves. Surf will be three to six feet on the south facing beaches of Ventura and Los Angeles Counties and four to seven feet along the Central Coast.

This swell will diminish slowly Saturday night and Sunday so the risk of moderate to strong rip currents and sneaker waves will also diminish slowly later in the weekend. Swimmers and anyone in the surf zone should remain vigilant through the weekend.

Watches, Warnings, Advisories

Ca, Beach Hazards Statement in effect through Saturday evening for zones 40-41-87. (See LAXCFWLOX). PZ, NONE.

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