11/128 AM.
A cooling trend will continue through Thursday, with cooler than normal temperatures expected across the area into the weekend. There is a chance of mountain and occasional lower elevation convection through at least Wednesday night. More robust marine layer cloud coverage is likely this week, however, higher clouds may disrupt the formation of the marine layer at times.
(Tue-Fri), 11/844 PM.
***UPDATE***
A somewhat active weather day occurred across the region today, depending on where you were. Some isolated, brief, heavy showers rushed through parts of Los Angeles County, though any reports were mainly under a tenth of an inch across The Basin, except for one report of 0.12 inches in the lower foothills of the San Gabriel Valley. The interior mountains of L.A. and especially Ventura and Santa Barbara counties had some slow moving thunderstorms, with heavy downpours, some gusty winds, and a total of 111 lightning strikes. As for temperatures, high temps were mainly in the 80s to 90s away from the costs, and the 70s closer to the coasts. Due to an influx of higher level clouds from the southwest, associated with a low pressure system, lower confidence in the reformation of the marine layer tonight. Low clouds may be patchy and intermittent, if they form at all.
Tomorrow, temperatures are expected to cool another several degrees across SW CA, with highs mostly in the 70s and 80s, with a few readings of 90s across the valleys, and in the low to mid 90s across the far interior areas. Thanks to the SW flow aloft, conditions will still feel humid.
Thunderstorm/shower chances will continue into tomorrow, with the afternoon and evening having the highest chances. For Ventura and Los Angeles, the highest chances will be for the interior mountains and the Antelope Valley. However, the aforementioned upper level disturbance will move into the Central Coast overnight into tomorrow, making the highest chances for all of San Luis Obispo County and northern Santa Barbara County. Brief, heavy downpours are possible, with dangerous lightning, and small hail anywhere a thunderstorm forms, however, across the mountains, localized flooding is possible.
Forecast looks in shape and no changes were needed for the evening update.
***From Previous Discussion***
Synoptically, the strong (594 dam) region of high pressure centered over the Four Corners region is going to move eastward over the next several days allowing a trough to drop down the CA coast, finally bringing some relief from the heatwave. By Friday the area will be near New Orleans before it begins to push back to the west. By late Tuesday it will be over north Texas.
A large thunderstorm has been centered over northern Ventura County for over an hour now, producing numerous lighting strikes and heavy rain. Isolated showers have also been observed from LA through western Ventura County. Expect the thunderstorm risk to persist into the late afternoon. It is definitely a day to check conditions before going to weather exposed areas like beaches or mountains. The greatest chc of convection will remain over far nrn VTA county and the eastern San Gabriel mtns. Some storms could roll off the mtns and in the Antelope and Cuyama Vlys as well.
Hgts will fall to 590 dam and this, along with mdt onshore flow in the afternoon, will bring 2 to 4 locally 6 degrees of cooling to the area. This cooling will bring most mtn and vly locations to below normal. Max temps today will most be in the upper 70s to mid 80s across the csts and upper 80s to mid 90s in the vlys.
There should be less high clouds tonight and this along with the mdt onshore flow should allow low clouds to form and move across most of the csts.
A trof sets up over the west cst on Wednesday. Hgts fall to about 585 dam. Onshore trends will bring strong onshore flow to both the N and E in the afternoon. The onshore flow, marine layer and lower hgts will all combine and lower max temps another 3 to 6 degrees. This cooling will bring below normal temps to almost the entire forecast area. Vly temps will range from 80 to 90 degrees or 5 to 10 degrees under normal.
The other issue Wednesday will the convective chcs. The upper level trough along the coast could bring in some additional moisture. This moisture combined with elevated instability will bring a 30 to 40 percent chc of convection to nrn VTA county and the eastern San Gabriels as well as a 10-15% chance of afternoon thunderstorms across much of SLO and Santa Barbara Counties.
The strong onshore flow will continue into Thursday. The troffing aloft and strong onshore flow at the sfc will likely produce a pretty robust marine cloudy layer extending into the vlys. Clearing will likely be on the slow side with some beaches remaining cloudy all day. Max temps will tumble another 3 to 5 degrees and its unlikely that any station will reach 90 degrees. Max temps in the vlys will likely end up 6 to 12 degrees blo normals.
The onshore push to the east will top out near 8mb both Wed and Thu afternoon. This strong push will generate gusty winds across the Antelope Valley and its foothills. There will be a 30 percent chc of low end wind advisories each afternoon.
By late Friday the high will begin it's return to our area and marking the slow return of increasing temperatures.
(Sat-Tue), 11/215 PM.
Good agreement with all of the medium range mdls, which show broad troffing with dry SW flow over the state. Hgts do climb through the extended period as the impressively large upper high expands back into our area from the southeast and nudges hgts up from 586 dam on early Saturday to 592 dam for Mon and Tue. At the sfc the mdt to stg onshore flow to the east will continue but the onshore push to the north will weaken substantially.
The weather not be very impactful. There will be plenty of night through morning low clouds and fog across the csts. The vlys will see less and less stratus and marine influence as the north push decreases and the hgts increase (smooshing the marine layer to under 1000 ft).
Gusty but still sub-advisory levels winds will continue across the Antelope Vly.
Temps will begin to warm on Saturday . Look for 2 to 5 degrees of warming on Saturday followed by 1 to 3 degrees on Sunday. The vlys will see the greatest amount of warming as the marine influence wanes. Despite the 2 days of warming, Sunday's max temps will remain 4 to 8 degrees blo normal. Monday's max temps will greatly resemble Sunday's. Minimal change into Tuesday.
12/0057z.
At 0021Z at KLAX, the marine layer was around 800 feet deep. The top of the inversion was near 2600 feet with a temperature of 26 C.
High confidence in the valley and desert TAFs with VFR conds expected. Gusty SW winds in the deserts should begin to subside between 04Z-06Z.
Low to moderate confidence in the coastal TAFs. IFR to LIFR conds expected along the Central Coast. There is a 30-40% chance of FG for KSBP and especially KSMX overnight between 08Z-14Z. IFR conds expected for KSBA and IFR to low MVFR for the Ventura and LA Coastal sites. The onset and dissipation times of low clouds may differ by +/- 2 hours from TAF times. CIGs may form and dissipate at times throughout the overnight period.
KLAX, Low to moderate confidence in the 00Z TAF. Low confidence in the arrival/dissipation time of CIGs, which could occur +/- 3 hours from TAF times. 30% chance that no CIGs occur. No significant east wind component expected.
KBUR, Moderate confidence in the 00Z TAF. There is a 40% chance of IFR CIGs 22/10-15Z.
11/957 PM.
High confidence that conditions will remain below Small Craft Advisory (SCA) across all of the southwestern California coastal waters through at least Friday night. However, localized gusts near 20 kt are possible each afternoon and evening off the coast of Long Beach through at least Thursday night. Patchy dense fog are possible on the Central Coast each morning. There is also a 5-10% chance of showers or a thunderstorm over the coastal waters through Wednesday.
11/217 PM.
High astronomical tides are expected to affect low-lying beaches south of Point Conception with the possibility of minor coastal flooding starting with the evening high tide through at least Wednesday. As a result, a Coastal Flood Advisory has been issued.
Predicted tide heights of up to 7.5 feet are expected between about 8 and 10 PM each evening. These tides, combined with a small increase in a long-period southerly swell, could result in minor flooding of sea water around the time of high tide over low-lying coastal areas such as parking lots, beaches, and walkways. Beaches most susceptible to potential minor coastal flooding issues include those around Point Dume and near Long Beach.
Ca, Coastal Flood Advisory in effect until midnight PDT Wednesday night for zones 349-350-354-362-366. (See LAXCFWLOX). PZ, NONE.
