19/100 AM.
Temperatures are expected to change little through Monday, with most areas remaining near normal. Morning low clouds and fog will return to many coastal areas each night through morning into early this week. A warming trend is expected by the middle of the week, as upper level high pressure builds into the area while onshore gradients weaken.
(tdy-Tue), 19/250 AM.
Very little change in the forecast this morning. 500mb heights over the region will remain fairly similar through Monday, bouncing between 589-592 dam, as a large/wide high pressure system persists over the Utah/Colorado/Wyoming area. Meanwhile, Tropical Storm Elida is rapidly weakening and still forecast to move northward, well off the coast to the west. Upper level flow will shift more SE today with Elida's movements and slight shifts in the aforementioned high pressure system.
Mid to high level clouds are already streaming into the region as a result of Elida's positioning, and there is a 5-10 percent chance of showers or thunderstorms over the Central Coast today and possibly Monday as a result.. At the same time, slight shifts in the high pressure system to the NE, will help bring some monsoonal moisture from the SE through Monday. This will result in continued mid to high level clouds across the region, as well as a 5-10 percent chance of a shower or thunderstorm focused over the interior mountains of Santa Barbara, Ventura, and Los Angeles counties, with highest chances on on Monday.
At the surface, little change in the pressure gradients will result in similar marine layer coverage each night. The little change in marine layer clouds, pressure gradients, and 500 mb heights will mean little change in temperatures through Monday. Temperatures will generally be near normal, with highs in the 70s to low 80s for the coast, mid 80s to mid 90s for the valleys and lower mountains/foothills, and 90s to around 100 for the deserts. As for Tuesday, a warming trend will commence, but information on the warming trend can be found in the long term discussion below.
As for winds, generally sub-advisory SW winds 25 to 40 mph can be expected each afternoon/evening across the Antelope Valley/adjacent foothills. Localized terrain enhancement could result in a few areas gusting to 45 mph (i.e Lake Palmdale). Sundowner winds will increase at least through Tuesday, and advisory level gusts are possible across SW Santa Barbara County by Tuesday evening.
(Wed-Sat), 19/250 AM.
Again, not much change in the long term forecast this morning. The large western U.S upper level high pressure center is forecast to drift to the area around New Mexico and the northern Texas Panhandle by Thursday. Southwestern CA will continue to be on the western periphery of this large upper level high, with 500 mb heights slowly increasing to 592-594 dam and continuing through the extended period.
As a result, the flow aloft will mostly be from the SE, bringing monsoon moisture into the region through much of the week. Precipitable water (PWAT) values are forecast to be 1.25 to 1.50 inches through much of the week for areas south of Point Conception and through mid-week for north of Point Conception. These PWATs are about 150 percent of normal for this time of year. Although the deepest moisture and is forecast to remain east of L.A. County during the extended period, it does look like the best chance of afternoon convection will come Wednesday and Thursday over the mountains of at least Ventura and L.A. Counties. However, right now chances remain around 10% for showers or thunderstorms across the mountains, and are too low to include in the official forecast at this time. As we draw closer to early this week, we should have a better idea of the chance and extent of afternoon convection for the middle of the week.
Otherwise, it looks like varying amounts of night and morning coastal low clouds and fog will prevail during the extended period, with a warming trend through the middle of the week. Moderate to high heat risk may expand into Wednesday or Thursday as pressure gradients weaken and maybe turn lightly offshore in the mornings with the potential for 500 mb heights building to 594-596 dam. There is a moderate chance (at least 60 percent chance) that at least Heat Advisories will be needed in some areas, including potentially near the coast, by Wednesday. Also of note, Sundowner winds in southern Santa Barbara Counties could reach near advisory thresholds into Wednesday and Thursday.
19/1300z.
Around 12Z at KLAX, the marine layer was 900 ft deep. The top of the inversion was at 2400 ft with a max temperature of 25 C.
High confidence in VFR TAFs for KPMD, KWJF, KBUR, KVNY, and KPRB.
Low to moderate confidence in remaining TAFs. CIG arrival and clearing times may be off +/- 3 hours and CIG heights off by +/- 300 ft. Presence of mid-level moisture is disrupting the marine layer and causing CIGS to bounce, scatter, and reform several times between 06Z-17Z each night through morning.
KLAX, Moderate confidence in TAF. Arrival and clearing times of MVFR CIGs 010-015 may be off +/- 3 hours of current forecast. 30% chance CIGs arrive as IFR 008-010 for a couple hours before lifting to MVFR after 08Z Mon. There is a 15% chance CIGs do not arrive or remain intermittent. No significant east wind component expected.
KBUR, Moderate confidence in TAF. 10% chance for IFR conds between 12Z and 16Z Mon. No wind issues expected.
19/911 AM.
Conditions are generally expected to remain below Small Craft Advisory (SCA) levels through Monday except for marginal SCA level northwest wind gusts across the Outer Waters more than 20 NM from shore and near Point Conception. Northwest winds will begin to strengthen Tuesday, rising to SCA levels by Wednesday and will likely last through late in the week.
A series of moderate period southerly swells will move through the waters starting late tonight and continuing through the week and likely beyond. These swells may impact south facing harbors, including the Port San Luis area.
19/917 AM.
Over the eastern Pacific, Tropical Storm Elida is forecast to move to the west-northwest well off the California Coast. Another tropical disturbance is expected to develop in the same area and follow a slightly more westerly track along 20 N Latitude. Both systems will produce moderate period southerly swells. High Surf Advisories and Beach Hazards Statements have been issued across Southwest California and are in effect this evening through Tuesday night.
The secondary system on the heels of Elida as well as an incoming long period, southern hemisphere, south swell arriving later this week will contribute to continued and potentially more hazardous beach conditions into next weekend. Additional High Surf Advisories and/or Beach Hazards Statements are likely needed next week.
Ca, High Surf Advisory in effect from 5 PM this afternoon to 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect from 5 PM PDT this afternoon through Tuesday evening for zones 340-346. (See LAXCFWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Monday for zones 673-676. (See LAXMWWLOX).
