Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

1107 am PDT Wed Jun 19 2019

Synopsis

19/723 AM.

For today through the rest of the period, strong onshore winds will keep low clouds over the coasts and valleys. There will be slow and limited afternoon clearing each day with possible drizzle in the morning. Temperatures will cool through Friday and warm slightly into the weekend as there will be better clearing.

Short Term

(tdy-Fri), 19/925 AM.

***UPDATE***

While the pattern is changing from the trof to high pressure ridging in from the west, the sensible weather will feel similar to yesterday's: coastal stratus that is slow to clear, gusty afternoon winds in Antelope Valley, and cumulus clouds over the Ventura and Los Angeles Co mountains. Not expecting as much rain as fell yesterday afternoon, but there may be brief, isolated showers over Ventura Co mountains this afternoon.

***From Previous Discussion***

Weak high pressure aloft will continue over the center of the state today with 588 DM hgts overhead. Moderate onshore flow both to the east and north will become very strong in afternoon as it follows the diurnal pressure curve. The marine layer is between 2500 and 3000 feet deep and low cloud cover all the of the csts vlys and cstl slopes. The very strong onshore flow this afternoon will limit clearing. There will likely be patchy drizzle as well but not as much as ydy morning as the marine layer is not deepening as much as it was ydy. It will continue to be rather unstable over the mtns but there is hardly any moisture so only expect some build ups and no showers. The strong onshore flow will bring gusty winds to the Antelope vly with isolated advisory level gusts near Lake Palmdale. In a study of contrasts the marine layer and onshore flow will keep the csts and vlys 5 to 10 degrees blo normal while the higher than normal hgts will bring interior temps 3 to 6 degrees above normal.

The ridge will be replaced with broad cyclonic flow on Thursday as a cold upper low pushes into the Great Basin. The onshore flow is forecast increase. This along with the lowering hgts and weak lift from the cyclonic flow will produce a great environment for morning drizzle. It would not be surprising if more than a few areas received a few hundredths of an inch of measurable precipitation from the drizzle. The foothill areas will likely see the heaviest drizzle due to the extra kick from the orographic lift. There will likely be less and slower clearing. Max temps will fall across the interior due to the lowering hgts. The coasts will see little change but the vlys will cool even further and will likely end up over degrees blo normals. The Antelope Vly will likely see advisory level wind gusts in the afternoon and early evening when onshore flow peaks near 10 MB to the east which exceeds the 97th percentile for onshore flow for this time of the year.

Friday should be a near repeat of Thursday except that there will be even lower hgts and perhaps more drizzle. Look for slow to no clearing its actually possible that the vlys will not clear or only partially clear. It will be the coolest day of the next 7 with max temps across the vlys and interior 12 to 18 degrees blo normal.

Long Term

(Sat-Tue), 19/320 AM.

Very weak ridging is expected over the weekend along with offshore trends - both of which will help the marine layer clouds clear earlier and allow afternoon high temperatures to rise some. By Sunday, temperatures will be near normal across the interior but will still be 5 to 10 degrees below normal across the coasts and valleys.

Another trof will arrive Monday, this time from the northwest, bringing back the strong onshore flow, less clearing and cooler coastal temperatures.

Aviation

19/1806z.

At 1703Z, the marine layer depth was around 2800 feet deep at KLAX. The top of the inversion was near 4800 feet with a temperature around 23 degrees Celsius.

Moderate confidence in the current forecast. The satellite picture trends definitely show better clearing patterns in the marine clouds and even coastal sections in LA county look good for clearing within the next 2 hours. There is still some doubt about clearing in the coastal sections of Ventura and southern Santa Barbara counties, however. The valley and desert TAF sites are well on their way toward clearing. Tonight, onshore flow will begin to increase along wih an anticipated deepening marine layer. Therefore, ceilings will be a bit higher at many TAF sites, however clearing trends will be slower and some coastal sites will remain cloudy on Thursday. Mountain obscuration will be a concern through Thursday.

KLAX, VFR conditions are expected this afternoon, followed by MVFR ceilings tonight and Thursday.

KBUR, VFR conditions are expected this afternoon, followed by MVFR ceilings tonight and Thursday.

Marine

19/904 AM.

Winds and seas will likely remain below Small Craft Advisory levels through at least Thursday. There is a 50 percent chance for advisory level seas and winds across the northern most outer waters Friday afternoon and evening, and a 30 percent chance of advisory level winds each afternoon and evening through the weekend.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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