08/104 AM.
Night through morning low clouds and patchy dense fog will be common over coastal areas and the coastal valleys through the weekend. Over the interior areas, hazardous heat will continue through this weekend and expand into the coastal valleys, with near to above normal temperatures around the beaches. Other than a small chance for mountain showers during the afternoon and evening hours through Sunday, dry conditions will prevail.
(tdy-Mon), 08/825 AM.
The latest satellite imagery indicate an upper-level ridge of high pressure over the Four Corners region. High pressure aloft will remain in place through the weekend, but weaken between Sunday and Tuesday. Onshore flow continues to weaken this morning and another very warm to hot and humid day is on tap for the area. Dangerously hot conditions will continue across the interior valley and foothills of the Antelope Valley. Temperatures in the mid 70s to upper 80s will be common today across the coastal sections, while temperatures will climb into the 90s to near 103 degrees in the coastal valleys today. Temperatures in the interior valley will be about about 10 degrees above normal with values climbing into the upper 90s to near 108 degrees. Heat Advisories and Extreme Heat Warnings remain in effect for the interior mountain mountains, interior valleys, and foothills of the Antelope Valley through Sunday evening. Elsewhere, widespread Heat Advisories are in effect for the weekend for the remaining valley, foothill, and mountain area, and some of the interior coastal sections. Even through most immediate coastal locales and beaches are not included in these advisories, residents will need to be mindful of the afternoon heat and take appropriate precautions as the added humidity will add some discomfort.
A cooling trend will take shape for early next week as 500 mb heights decline some as the upper-level ridge weakens. An increase in onshore flow will bring some cooling over the coming days and should bring a much more pronounced low cloud field to the coastal areas.
Due to the ridge positioning, the area will sit on the fringe of subtropical moisture being drawn up by the circulation around the high pressure system. Southeast flow aloft will transport marginal amounts of monsoonal moisture into the region. The latest deterministic solutions and some of the ensemble members suggest an slight bump up in cloud cover and possible convection on Sunday afternoon and evening as weak shortwave moving around the ridge moves over the region. There will be a 5-15 percent chance of afternoon and evening convective showers or thunderstorms through the weekend, highest over the Los Angeles County and Ventura County mountains. If the steering flow become more favorable for some areas or the weak shortwave strengthens a bit more than anticipated, a few showers could steer into the coastal, valley, and other mountain areas. This will need to be monitored by future shifts for development. If thunderstorms do occur, there is the possibility that dry lightning may result, and may cause fire starts, adding to the fire weather concern. The increase in monsoonal moisture along with the warmer than normal sea temperatures will also increase humidities allowing for warmer than normal overnight lows and add some humidity during the daytime to increase heat impacts.
Increasing onshore flow will likely bring an stronger sea breeze each afternoon and evening and possibly gusty southwest winds during the afternoon and evening hours across interior sections including the Antelope Valley. The strongest onshore winds are expected to be on Sunday, based on projected surface pressure gradients. The gusty winds across the interior in combination with the hot and dry conditions will produce elevated to brief critical fire weather conditions.
(Tue-Fri), 08/235 AM.
Very little change in the long term forecast compared to yesterday. 500 mb heights will continue to drop to at least 592 dam through Friday, and maybe even lower. At the same time, onshore flow will increase both to the north and the east becoming strongly onshore in both directions in the afternoons. The marine layer will respond to this and low clouds will likely begin to extend into the valleys. Look for slower than normal clearing and some west facing beaches may see only limited clearing each afternoon and evening.
The combination of a deeper marine layer, stronger onshore flow, and falling heights will bring 2 to 3 degrees of cooling each day through Thursday. Maximum temps will largely be below normal by Tuesday, and by Wednesday, valley temps will be in the 80s with maybe a few degrees of 90s. In other words, finally a "cooler" period of time this summer.
PWs will remain elevated through the period, however. In combination with warmer than normal ocean temperatures off the immediate coast, conditions will continue to feel a little more humid than normal. It will also keep overnight lows a little warmer than normal. The region will remain on the fringe of the monsoonal moisture through at least Wednesday, with the elevated moisture and increased instability keeping the low chance (10 to 15 percent) of afternoon mountain convection going. By the end of next week, medium-range model guidance indicates the potential for an upper low to develop off the Central California Coast, east of which large-scale ascent and convective chances could modestly increase next Thursday and Friday.
Additionally, the strong onshore flow to the east will produce near advisory level wind gusts across the western Antelope Valley and the western foothills each afternoon and evening. Gusty sundowner winds will also be possible early next week in southern Santa Barbara County.
08/1746z.
At 1639Z at KLAX, the marine layer was 800 feet deep. The top of the inversion was at 3600 feet with a temperature of 27 C.
High confidence in VFR TAFs for KPRB, KBUR, KVNY, KPMD & KWJF.
Low to moderate confidence in remaining TAFs due to uncertainties in coverage and timing of low clouds and LIFR/IFR conds tonight into Sun morning. Some mid-level moisture and warm sea surface temps will disrupt the formation of marine layer. This will likely result in intermittent CIGs especially for KLAX, KSMO, & KLGB. CIG heights accurate within +/- 200 ft of current forecast.
KLAX, Fair confidence in TAF. Intermittent CIGs (007-010) possible 03Z-15Z Sun. No significant east wind component expected.
KBUR, High confidence in VFR TAF. No wind issues expected.
08/819 AM.
Winds and seas are expected to remain largely below Small Craft Advisory (SCA) criteria across the coastal waters through Wednesday night. However, northwest winds locally gusting to 20-25 knots in typically windy areas around and to the south of Point Conception can be expected each afternoon and evening through Sunday.
Dense fog may affect portions of the coastal waters each night through morning this weekend and possibly into early next week.
08/819 AM.
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 Monday and continuing through at least Wednesday.
Predicted tide heights of up to 7.5 feet are expected between about 8 and 10 PM each evening. These tides, combined with an 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, Extreme Heat Warning in effect until 8 PM PDT Sunday for zones 38-377-381>383. (See LAXNPWLOX). Heat Advisory in effect until 8 PM PDT Sunday for zones 88-342>345-348-349-351>353-356>358-367>376-378>380-548. (See LAXNPWLOX). PZ, NONE.
