16/246 PM.
Night through morning marine layer clouds will mainly be confined to the coast much of this week. Warmer and drier conditions are expected away from the immediate coast this week, with peak heat likely being Tuesday through Thursday when moderate heat risk is expected in warmest locations.
(tdy-Wed), 16/235 PM.
Upper level ridge of high pressure beginning to expand westward over southern California today with rising heights. This in combination with slight weakening of onshore pressure gradients has started a warming and drying trend, with many interior areas climbing well into the 90s today. As heights continue to build the next couple of days and onshore pressure gradients weaken slightly, looking for marine layer cloud coverage to become less extensive, mainly confined to the coast.
The warming trend remains on track through much of this coming week, with heat likely peaking Tuesday-Thursday. 500 mb heights will continue to increase gradually through Tuesday before plateauing as the large area of high pressure across the Southern United States marches westward. This combined with weakening onshore flow will swing temperatures right back up to around 5-10 degrees above seasonal normals in the Tuesday-Thursday time frame. Overnight temperatures will increase each day as well with most areas south of Point Conception seeing lows drop down to only the mid 60s to low 70s, with many foothill and mountain locations seeing minimum temperatures in the mid 70s to lower 80s by mid week. For the peak of the heat Tuesday through Thursday, warmest valley, lower mountain, and desert locations are expected to range between 95 and 105 degrees.
With afternoon forecast, have included heat advisories for Tuesday through Thursday for areas that have highest confidence for moderate heat risk including the warmest mountain and valley locations (including San Fernando, San Gabriel, and Santa Clarita Valleys). There is a 30-50 percent chance of heat advisories being expanded to include more areas, with potential considerations including LA interior coast (downtown LA), the Ventura county valleys, and Santa Monica mountains. There is increasing confidence that Downtown LA will top 90 degrees sometime between Tuesday and Thursday. The warmer overnight lows will also add to the heat discomfort, especially in LA county. The shallow marine layer will help likely help keep temperatures at immediate coastal areas moderate during the warm up.
Gusty northwest to north winds will begin increasing tonight across southwest Santa Barbara County as well as interior mountain areas, especially the I-5 corridor near the Grapevine. While winds are expected to generally remain sub-advisory levels the next few days, there is a moderate chance for winds to reach advisory criteria in portions of southwest Santa Barbara County Monday night. The focus of the sundowner winds each evening will be from Gaviota to San Marcos Pass, with the Monday evening event likely generating gusts up to 45 mph near Gaviota/Refugio. The peak Santa Barbara-Santa Maria gradient on Monday evening is expected to be -4 mb. The sundowner winds this week will bring some warning into the 80s to lower 90s in windy canyons/foothills by Monday evening, then slightly warmer the following few evenings as the air mass warms up. These increasing winds across southwestern SB County may also delay or completely hinder the formation of marine layer clouds across the south coast of the county as well as Ventura County. If the marine layer does in fact not develop over these areas, temperatures could be warmer than advertised.
(Thu-Sun), 16/245 PM.
Upper level ridging will continue to bring warm and dry conditions to Southwest California through the work work. Onshore flow will also be its weakest Wednesday through at least Friday. The resulting widespread Moderate Heat Risk will also lead to a moderate chance for heat headlines away from the coast through at least Thursday, but increasing model agreement for Friday brings it into play as well. The marine layer will likely be confined just to the immediate coastal areas, and there is a small chance that dense fog will occur as the marine layer depth will be quite shallow.
Friday through next weekend, there maintains some uncertainty in the evolution of the upper level pattern. Cluster analysis still shows fairly similar chances of weak troughing setting up along the coast vs the ridge maintaining its position out west. Suffice to say confidence from Saturday on is fairly low. While the former solution favor a cooling trend, the latter favor continued hot weather and even a small chance for monsoonal convection. The current heat advisories that are in effect Tuesday-Thursday may need to be extended into Friday or even next weekend if the warmer solution verifies.
While winds aren't expected to be of any widespread significance, the increasing northerly pressure gradient will likely allow for gusty north to northwest winds each night across the interior mountains (especially the Grapevine), deserts, and southwest Santa Barbara County. While widespread advisory level winds aren't likely in the extended period either, there is a chance for portions of southwest SB County to reach advisory levels. As in the short term, increasing northerly winds across southwestern SB County could disrupt the formation of marine layer clouds across the south coast of the county as well as Ventura County. Again, this could result in warmer temps along the coasts.
16/1800z.
At 1719Z at KLAX, the marine layer was at 1300 feet deep. The top of the inversion was near 4600 feet with a temperature of 23 C.
High confidence in VFR TAFs for KPRB, KBUR, KVNY, KPMD & KWJF.
Low to moderate confidence in remaining TAFs, lowest south of Point Conception. Arrival times of IFR/MVFR conds tonight may be off +/- 2-3 hours. Patchy marine layer may also cause conds to bounce between VFR and MVFR/IFR later tonight and Mon morning.
KLAX, Low to moderate confidence in TAF. Arrival of cigs tonight may be off +/- 2-3 hours from TAF with 40% chance of IFR. Cloud coverage may bounce between SCT and OVC late tonight and Mon morning. There is also a 20% chance no cigs late tonight. No significant east wind component expected.
KBUR, High confidence in VFR TAF.
16/103 PM.
Moderate to high confidence in forecast. Current Small Craft Advisory (SCA) for gusty winds over the outer waters from near Point Conception southward to San Nicolas Island and in the vicinity of the Channel Islands looks on track. Good chance for SCA winds to be ongoing from through much of the week over the outer waters, with SCA winds expanding into the northern outer waters Monday afternoon/evening.
For the inner waters, SCA winds are possible late this afternoon and evening S of Point Conception, and for the Santa Barbara Channel and inner waters north of Point Sal Monday through Wednesday. Thursday through Friday looks more favorable for SCA winds for the inner waters north of Point Sal.
Building short period seas are expected over the next several days, likely rising to around 7-9 feet over the outer waters.
Ca, Heat Advisory in effect from 10 AM Tuesday to 8 PM PDT Thursday for zones 38-88-343>345-351-353-371>373-375-376-379-380-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Tuesday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 6 PM this evening to 3 AM PDT Monday for zone 655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Wednesday for zones 673-676. (See LAXMWWLOX).
