17/105 PM.
Minimal changes expected over the next few days in the way of temperatures. Morning low clouds and fog will return to many coastal areas each day through early next week. A warming trend is expected by the middle of next week as upper level high pressure builds into the area while onshore gradients weaken.
(tdy-Mon), 17/1224 PM.
Not much change in the upper level pattern over srn CA thru Sun with the region under the SW periphery of a large western U.S. upper level high centered mainly between WY and CO. H5 heights over the forecast area will be generally in the 589-591 dam range thru the period. The upper level flow will start out mostly southerly thru Sat then turn more SE into Sun. Some monsoonal moisture will push back into SW CA this weekend with an increase mid level clouds at times, and by Sun some afternoon cu buildups cannot be ruled out in the mtns along with a non-zero chance (5-10%) of a shower or thunderstorm focsued in the VTU/L.A. County mtns with about a 5 percent of a shower just about anywhere tonight. Even so, it looks like the bulk of the monsoonal moisture will remain east of L.A. County thru Sun. A rapidly weakening tropical cyclone will past well to the west Sunday into Monday and may provide a bump in moisture across the region including the Central Coast being closest to the system. The most likely scenario is a bump up in mid to high clouds especially for northern areas, however, there is a 5-10 percent chance of a shower or thunderstorm, especially into Monday.
Pressure gradients will be onshore and increase over the next couple of days. This will support near normal temperatures along with an increase in coastal night and morning low clouds and fog. Afternoon highs should range from the 70s to low 80s for the coast, mid 80s to mid 90s for the vlys and lower mtns, and 90s to around 100 for the deserts.
(Tue-Fri), 17/1224 PM.
The large western U.S upper level high center is forecast to drift S from Colorado on Mon to the area around New Mexico and the northern Texas panhandle by Thu. Southwestern CA will continue to be on the western periphery of this large upper level high, with H5 heights slowly increasing to 592-594 dam during the extended period.
The flow aloft will mostly be from the SE with monsoonal moisture expected to continue to push into the area. Precipitable water values are forecast to be in the 1.25 to 1.40 inch range for the most part which is about 150 to 160 percent of normal for this time of year. Although the deepest moisture and instability 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. For now, there is only a minimal chance of showers late Thu in the fcst for the eastern L.A. County mtns. Otherwise, there is a non-zero chance (10%) for a thunderstorm to develop in the mtns especially Wed and Thu. As we draw closer to early next week, we should have a better idea of the chance and extent of afternoon convection for the middle of next week.
Otherwise, it look like varying amounts of night and morning coastal low clouds and fog will prevail during the extended period, with a warming trend thru the middle of next 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. There is a moderate (50-60 percent chance) that at least Heat Advisories will be needed in some areas, including potential near the coast.
17/1736z.
At 1700Z at KLAX, the marine layer was 2000 ft deep. The top of the inversion was at 4500 ft with a max temperature of 23 C.
High confidence in VFR TAFs for KPMD and KWJF.
Low confidence KPRB, KBUR, and KVNY. There is a 30% chance for IFR conds at KPRB after 10Z. There is a chance VFR conds prevail at KBUR (40%) and KVNY (50%). If cigs do arrive, lower confidence in timing of cig which could be up to 4 hours earlier than forecast, and min cig height may be off by +/- 300 feet.
Moderate confidence in remaining TAFs. Cigs expected at each site, except for a 25% chance no low clouds at KSBP tonight. Flight cat changes may be off by 3 hours, with lowest confidence in time for KSBP and KSBA. Min cig heights may be off by +/- 200 feet.
KLAX, Moderate confidence in TAF. Arrival of cigs may be as early as early as 01Z or as late as 06Z. 10% chance for brief OVC008-009 cigs before 10Z. 30% chance of an east wind component reaching 6 kt overnight into Sat morning.
KBUR, Low confidence in TAF after 06Z. 40% chance VFR conds prevail. If cigs do arrive, lower confidence in timing of cig which could be up to 4 hours earlier than forecast, and min cig height may be off by +/- 300 feet.
17/105 PM.
Marginal Small Craft Advisory (SCA) northwest winds (20-25 kt) and seas will impact the waters beyond 20 NM from shore (except for nearshore along the Central Coast) through tonight. Localized gusts to 25 kt may occur in the far western portion of the Santa Barbara Channel through this evening. Then conditions are expected to remain below SCA levels through Monday except for fairly localized SCA level northwest wind gusts across the Outer Waters more than 20 NM from shore. Northwest winds will begin to strengthen Tueday and SCA conditions are expected to occur much of next week.
A series of moderate period southerly swell will impact the waters late Sunday through much of next week which may impact south facing harbors, including the Port San Luis area.
17/105 PM.
Over the eastern Pacific, Tropical storm Elida is forecast to strengthen to hurricane status tomorrow. It is then expected to move to the north and west well off the Baja coast. Another tropical disturbance is expected to strengthen next week and generally follow the path of Elida to the northwest. Both systems will produce moderate period southerly swells. High Surf Advisories and Beach Hazards Statements have been issued across Southwest California from Sunday evening through Tuesday night. The secondary system on the heels of Elida and an incoming long period southern hemisphere south swell forecast to arrive sometime late next week will likely contribute to continued and potentially more hazardous beach conditions into the following weekend. Additional High Surf Advisories and/or Beach Hazards Statements are likely next week.
Ca, High Surf Advisory in effect from 5 PM Sunday to 11 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect from Sunday afternoon through Tuesday evening for zones 340-346. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 9 PM PDT this evening for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zones 670-673-676. (See LAXMWWLOX).
