28/112 PM.
Temperatures will peak this weekend, then a significant cool-down is expected to begin Monday, with close to normal temperatures through much of the week. There is a chance for coastal dense fog tonight into Sunday morning. Much cooler conditions expected Tuesday through at least Thursday, along with gusty winds and a chance of rain at times.
(tdy-Tue), 28/112 PM.
The upper level high that has dominated the overall pattern for West Coast will continue to break down over the next few days. Then a mostly zonal, but slight troughing will occur at upper levels by Tuesday. High temperatures will peak today and tomorrow, with slightly warmer temps tomorrow as onshore flow weakens. A dramatic cool-down is on tap Monday and high temperatures will be within 5 degrees of normal across most of Southwest California for this first time in quite a while, at least for people living outside of the marine layer influences. By Tuesday, further cooling will bring temps back down to normal for this time of year.
As for the marine layer, expecting slightly less coverage away from the immediate coasts tonight into Sunday morning, with dense fog likely becoming more of an issue across all coastal areas, especially north of Point Conception. Some guidance is also suggesting no marine layer coverage south of Point Conception, but decided to go with more persistence for tonight. Due to the uncertainty of marine layer coverage, confidence in high temps near the coasts is lower. A much deeper and expansive marine layer is likely Monday and Tuesday, and there is a chance for no clearing as coastal locations each of these days.
Onshore winds will be common each afternoon over the next few days, increasing in strength some on Monday and again Tuesday. Although winds appear to remain below advisory levels, cannot rule out localized gusts to 45 mph over the Antelope Valley and Foothills. Tuesday poses the best chance for more widespread advisory level winds over the Antelope Valley and Foothills, and potentially higher mountains across interior LA County.
Very dry air across the interior and even coastal valleys such as the San Fernando Valley will be common through Monday, then relative humidites will increase Tuesday as the marine influences finally make their way further inland.
A slight chance of light rain begins Tuesday, especially north of Point Conception. Any rain will be very light, if any at all on Tuesday. More details for next week's rain are in the long term portion of the discussion.
(Wed-Sat), 28/112 PM.
A cool period is on tap for the middle of next week across much of the region on Tuesday as 500 mb heights continue to decrease and onshore flow slightly increases. Additionally, a fairly deep and expansive marine layer will be common through at least Thursday. Little change will be felt and temperatures will hover near normal for this time of year. An increase in temperatures is expected as early as Friday of next week when 500 mb heights rebound some under weak ridging, and highs will likely increase to 5-10 degrees above seasonal normals by next weekend.
The upper level low swinging across the Pacific Northwest next week that will influence the noticeable cool-down has shown a slight chance to chance of rain across the region Tuesday- Thursday over the past week or so. However, the downward trend in rain totals is continuing, and the chances for any rain greater than 0.25 inches have become quite bleak, and rain totals, if any, will likely be less than 0.25 inches, trending more towards 0.10 inches or less.
Onshore flow will increase slightly under the influence of the trough's passage to the north through Thursday. The Antelope Valley (AV) and foothills and interior mountains of Los Angeles County will see the strongest winds during this period, but overall wind speeds are still favored to be just under advisory levels. However, this will need to be monitored as we move more into the higher resolution data timeframe. Additionally, temps across the AV may increase slightly with the compressional heating due to downsloping flow. By Friday, both the EC and GFS indicate light offshore flow, ushering in dryer air to the region.
28/1718z.
At 1641Z at KLAX, the marine layer was 800 ft deep. The top of the inversion was at 2800 feet with a temperature of 21 C.
High confidence in VFR TAFs for KPRB, KPMD, KWJF, KBUR, and KVNY.
Low to moderate confidence in remaining TAFs.
For KSBP & KSMX: expecting return of V/LIFR conditions. Timing of CIG/VSBY restrictions may be off +/- 2 hours.
For TAFs south of Point Conception: expecting return of LIFR to low-end IFR at times. Timing of CIG/VSBY restrictions may be off +/- 3 hours.
KLAX, Low to moderate confidence in TAF. Arrival and clearing times of CIGs may be off +/- 3 hours. Expecting IFR to low-end IFR conds generally (003-007 with 3-6SM vsbys) No significant east wind component expected.
KBUR, High confidence in VFR TAF.
28/742 AM.
High confidence in winds and seas staying under Small Craft Advisory (SCA) levels through at least Monday, except for a 30-50% chance of low-end SCA winds beyond 20 NM from the Central Coast Sunday evening through Monday night.
Moderate risk of dense fog with visibility under one mile will continue in the near-term (night through morning).
There is a growing risk for widespread strong SCA or low-end Gale Force winds over most coastal waters (including nearshore and the Santa Barbara Channel) late Thursday through Friday of next week.
Ca, NONE. PZ, NONE.
