13/108 AM.
Cooler than normal temperatures and widespread marine layer clouds will continue through the weekend. There is a low chance of showers/thunderstorms through this afternoon.
(tdy-Sat), 13/807 AM.
The latest water vapor imagery indicates a weak trough of low pressure aloft moving into the Central Coast of California this morning. A deep marine layer depth in place has pushed clouds into the coastal slopes and in the interior valleys for areas north of Point Conception this morning, and into the valley south of Point Conception. Instability with trough has lifted the marine layer cloud deck and squeezed out drizzle or light rain along the Central Coast this morning. PoPs have been nudged up in the latest update and mentions of more widespread showers added to the forecast for this morning. A cooling trend is expected to continue across the region today.
***From Previous Discussion***
The trough along the coast has finally settled in. Mid-level clouds are streaming in from the southwest, temperatures will continue to cool, and there remains a small chance for convective activity today.
The low chance of showers/thunderstorms continues through this afternoon across the area, with highest chances (15% chance) across the Central Coast as well as the northern Ventura/interior Santa Barbara County mountains. While high resolution CAMs really don't show much in the way of reflectivity, there is fairly widespread elevated instability associated with this trough across Santa Barbara and SLO Counties, as well as some left over monsoonal moisture to play with through later this morning. A small lobe of vorticity is projected to swing across the northern part of our CWA now through this morning. This could be the best opportunity for storm initiation through the day, although afternoon heating and orographics could be the best source across the interior areas. At lower elevations, the more significant impacts could be gusty winds and dry lightning, while higher terrain would potentially see higher rainfall rates--although not expecting storms of the same magnitude as Tuesday's storms. Very low chances for showers/thunderstorms exist into the weekend as the trough remains almost stationary along the coast. However, the environment will become rather mositure starved, so not expecting much in the way of rainfall if any storms get going.
Aside from the small chance for storms to develop, the most significant aspect of the forecast is the continued cooler than (mid-August) normal temperatures region-wide. Thanks the the lower 500 mb heights brought along by the trough as well as moderate to strong onshore flow, a very long stretch of above normal temperatures has ceased. Friday's max temps are forecast to be very similar to today, around 8-15 degrees above normal in many places. We are expecting a couple degrees of warming on Saturday, but still well below seasonal normals.
A very deep marine has already expanded to many valleys. Fairly similar coverage is expected Friday, with slightly less coverage Saturday due to a shrinking marine layer depth. The marine layer will burn off in the late morning to early afternoon, although some west facing beaches may not see much in the way of clearing as the onshore flow will try to keep the clouds in place. Additionally, there is a chance for some patchy drizzle this morning and again Friday morning. There is potential for mid level clouds to disrupt the radiative cooling processes that help the marine layer form. This could create more of a patchy marine layer, with highest potential for this across LA and Ventura Counties.
Enhanced onshore flow means fairly gusty west to southwest winds will be common across the interior, with winds likely the strongest across the Antelope Valley and foothills. While some advisory level wind gusts may occur, not expecting these winds to be widespread enough to warrant an advisory at this time.
(Sun-Wed), 13/104 AM.
The extended period will generally feature rather benign sensible weather relative to the time of year. The upper level ridge of high pressure over the southern United States will push the trough to the west. 500 mb heights will increase to around 592-594 dam with dry southwest flow aloft. 500 mb heights are projected to peak Tuesday/Wednesday. Additionally, onshore flow is expected to weaken some to some, with the LAX-BFL pressure gradient even forecast to become negative by next week.
Marine layer clouds will shrink each day with increasing 500 mb heights and weakening onshore flow, likely retreating to just the coastal areas by early next week. By Tuesday, increasing northwest flow will likely wipe out the marine layer from southern Santa Barbara County and potentially Ventura County.
With 500 mb heights increasing, onshore flow weakening, and marine layer coverage shrinking, temperatures will climb to near normal for mid-August. The more noticeable increase in temperatures will be across the valleys and interior since most coastal areas will still be under marine influences.
Increasing northwest flow next week will likely bringing gusty winds in the afternoon through late evening hours to Southwestern Santa Barbara County as well as the interior mountains, especially along the I-5 through the Grapevine.
13/1727z.
At 1612Z at KLAX, the marine layer was 2900 feet deep. The top of the inversion was near 4500 feet with a temperature of 18 C.
High confidence in VFR TAFs for desert airfields (KPMD & KWJF).
Moderate confidence in remaining TAFs. Timing of change groups may be off +/- 2 hours. Expecting little to no clearing of MVFR CIGs 015 to 030 excluding KBUR/KVNY. No clearing is most likely for KSBP and KSMX (80% chance).
KLAX, Moderate confidence in TAF. Clearing of MVFR CIGs 025-030 likely around 13/20Z. MVFR CIGs expected to return around 14/01Z (+/- 3 hours). There is 30% chance of no clearing. No significant east wind component expected
KBUR, Moderate confidence in TAF. No wind issues expected
13/738 AM.
High confidence that conditions will remain below Small Craft Advisory (SCA) criteria across all coastal waters through Friday morning. Low to moderate chances for SCA winds across favored areas south of Point Conception this weekend. Increasing chances across all coastal waters heading into next week, with local gusts of 30-35 kt possible at times around Point Conception. Seas may approach 10 ft across portions of the Outer Waters Tuesday and Wednesday.
There is a very small chance of a shower nearshore from Point Conception to the north through this morning.
Ca, NONE. PZ, NONE.
