Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

810 pm PDT Sat Jun 24 2017

Synopsis

A strong ridge of upper-level high pressure over Southern Arizona will continue very warm conditions away from the coast through early next week. Closer to the coast, a persistent marine layer should moderate temperatures and continue mainly night through morning low clouds and fog. A trough of low pressure off the California Coast will weaken high pressure aloft Tuesday and bring a cooling trend as onshore flow strengthens.

Short Term

(tonight-Tue)

Some mid level moisture combined with extreme heating and associated instability to generate some high based thunderstorm activity this afternoon across the mountains and Antelope Valley. Since the lower levels of the atmosphere were so dry, very little rain fell with these storms, with dry lightning and gusty downdraft winds being the main threats. With the loss of daytime heating, the thunderstorm activity has ended this evening. As far as low clouds and fog are concerned, it will mostly be focused across the Central Coast and LA county coast tonight into Sunday morning.

The main weather story continues to be the long duration heat wave over interior sections of Southwest California. Record high temperature at Lancaster (110 degrees) today, with records tied at Palmdale (109 degrees) and Sandberg (96 degrees). The combination of a slight increase in heights and a weak northerly flow near the surface on Sunday morning will bring increasing boundary layer temperatures to much of the region on Sunday. The Antelope Valley and mountains will continue to see the very hot conditions where heat warnings and advisories have been in effect this entire week. The most noticeable increase in temperatures tomorrow will be across the valleys where there will once again be some triple digit readings in warmest locations. With projected temperatures of 100-105 degrees in the Santa Clarita Valley on Sunday, have included them in the heat advisory product with the evening update. Some gusty sundowner winds will also bring warming temperatures to the Santa Ynez mountains and SBA south coast next couple of evenings. While SBA- SMX gradient is expected to reach -4 mb tonight as well as Sunday and Monday nights, there is not much upper level wind support. As a result, expecting winds to be fairly localized between Gaviota and Goleta, with gusts locally reaching 35 to 40 mph in favored areas. The combination of hot and dry conditions along with locally gusty winds will continue to bring elevated fire danger and even brief critical fire weather conditions through Monday across interior sections of the forecast area, see fire discussion below for more details.

*** From previous discussion ***

A slow cooling trend will begin Monday and continue into Tuesday as the ridge aloft weakens and a trough approaches OR and northern CA. Marine lyr likely will remain confined to the Central Coast and LA County as there's a strong enough northwest gradient to limit the northward push of the low clouds through the bight.

Long Term

(Wed-Sat)

Cooling trend to continue into Wed and then little change Thu before a ridge begins to develop Friday into Saturday and temps. Marine lyr expected to deepen and expand to all coast/valleys by mid week but clear off to the beaches. High temps should fall back to normal levels Tue or Wed then a little below normal Thu before rebounding slightly going into the weekend.

Aviation

24/2335z.

At 2330Z at KLAX, the marine layer depth was around 1200 feet. The top of the inversion was around 3800 feet with a temperature near 30 degrees Celsius.

Low to moderate confidence in the 00z TAFs. Mid level moisture disrupted the marine layer clouds this morning. The marine clouds should regroup again with IFR/LIFR conditions becoming reestablished in mainly the LA coastal sections and Central Coast tonight. Isolated thunderstorms with gusty downdraft winds across the mountains and deserts til sundown.

KLAX, Low to moderate confidence in the 00z TAF. The marine clouds will return with IFR/LIFR conditions tonight. There is a 30 percent chance of the marine clouds arriving plus or minus two or more hours from the forecasted time.

KBUR, Moderate confidence in the 00z TAF. There is a 20 percent chance of marine clouds sneaking into the airfield early Sunday morning. Otherwise, VFR conditions are expected through Sunday.

Marine

24/900 PM.

Winds will continue to gradually increase through the weekend. A Small Craft Advisory remains in effect for the Outer Waters through early Monday morning, but this advisory will likely be needed through at least Wednesday. Across the Inner Waters, there is a 70 percent chance of Small Craft Advisory level winds developing each afternoon and evening across the Northern nearshore waters and the East Santa Barbara Channel. Local gusts up to 25 kt could also develop across the portion of the Inner Waters from Point Mugu to San Mateo Point west of Santa Catalina Island. In addition, a short- period west to northwest swell with a period around 6 seconds could impact the coastal waters between Monday and Wednesday. A mix of short-period seas and/or winds could develop across the entire coastal waters into midweek next week.

Watches, Warnings, Advisories

Ca, Heat Advisory in effect until 9 PM PDT Sunday for zones 38-52>54-88. (See LAXNPWLOX). Beach Hazards Statement in effect until 10 PM PDT this evening for zones 40-41-87. (See LAXCFWLOX). Excessive Heat Warning in effect until 9 PM PDT Sunday for zone 59. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 9 PM PDT this evening for zones 645-650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Monday for zones 670-673-676. (See LAXMWWLOX).

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