06/214 PM.
Night through morning low clouds and fog will be common over coastal areas and the coastal valleys through at least this weekend, with clearing each afternoon. Hazardous heat will occur through this weekend over interior areas. Aside from the chance of a few mountain showers on Sunday, dry conditions will prevail.
(tdy-Sun), 06/1249 PM.
***UPDATE***
Little change in the pattern through the short term, with a ridge of high pressure aloft centered near the four corners region. This ridge will remain more or less stationary through Friday and then expand westward so that heights rise over southern California. Heights aloft will rise to 596 dam by Saturday before decreasing some into Sunday. Gradual warming is expected through the next couple of days, and Saturday is likely to be the warmest day in this stretch of heat. The highs Friday through Sunday will be around 4 to 8 degrees above normal, and locally 10 degrees above normal. There is lower confidence in temps for the nearshore areas due to variations in the strength of onshore flow and the extent of the marine layer. Heat advisories and warnings are in effect for the lower mtn elevations and the far interior. Even through the coastal vlys are not included in these advisories, residents will need to be mindful of the afternoon heat and take appropriate precautions.
Onshore winds are expected to be gusty and persistent through the short term, increasing during the afternoon and evening hours across interior sections including the Antelope Valley. The strongest onshore winds are expected to be later today and on Sunday, based on projected surface pressure gradients. In general, onshore gradients to the northeast and north (LAX to Daggett and LAX to Bakersfield) will weaken some Friday, then strengthen Saturday and especially Sunday. The gusty winds across the interior in combination with the hot and dry conditions will produce elevated to brief critical fire weather conditions.
Monsoonal moisture will begin to move over the area today with southeast flow aloft, due to the position of the upper high over the Desert Southwest region. This flow pattern aloft will draw subtropical moisture across the area, mainly at levels above around 600 mb. Precipitable water values today will increase from 1.0 inch to near 1.25 inches, but probability forecasts show the best chances of showers or thunderstorms will remain east of LA County this afternoon and evening. There is still a low (10-15%) chance of convective activity over the eastern San Gabriels and eastern Antelope Valley today. Chances will remain low through Saturday, but some ensemble members show a better chance on Sunday.
The increase in monsoonal moisture will also increase humidities closer to the surface, at least for the coast and near-coastal areas. Along with the warmer sea surface temperatures, this will tend to increase heat impacts during the daytimes and keep overnight lows warmer than normal.
Low clouds and fog will continue to affect coastal areas and some of the coastal valleys during the night to morning hours through the short term. This pattern could be disrupted depending on the amount of monsoonal moisture aloft, which could slow or prevent marine layer formation.
(Mon-Thu), 06/132 PM.
Cooling will finally arrive on Monday, with a gradual cooling trend through the long term. The ridge will slowly weaken as a series of weak trofs moves through OR and far nrn CA. Hgts will fall to 592 dam. 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 xtnd into the vlys. 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 hgts will bring 2 to 3 degrees of cooling each day Monday through Thursday. Max temps will approach normals on Tuesday and then most areas will see blo normal max temps on Wed and Thu. Vly temps on Wed and Thu will only be in the mid 80s to lower 90s.
PWs will remain elevated through the period, however. This in combination with warmer than normal ocean temperatures off the immediate coast will continue to make things feel a little stickier than normal. It will also keep overnight lows a little warmer than normal. We will remain on the fringe of the monsoonal moisture through at least Wednesday. The elevated moisture and increased instability will keep keep the low chc (10 to 15 percent) of afternoon mountain convection going.
The strong onshore flow to the east will produce gusty near advisory level wind gusts across the western Antelope Vly and the western foothills.
06/1826z.
At 1727Z at KLAX, the marine layer was 900 feet deep. The top of the inversion was at 2700 feet with a temperature of 27 C.
High confidence in TAFs for KPRB, KBUR, KVNY, KPMD & KWJF.
Moderate confidence in remaining TAFs. Timing of flight cat restrictions may be off +/- 2 hours, and CIG heights by +/- 200 ft.
KLAX, Moderate confidence in the 18Z TAF. CIGs expected to return 04Z-16Z, but timing could be off by +/- 2 hours from TAF times. 40% chance conds dip to IFR overnight. No significant east wind component expected.
KBUR, High confidence in the 18Z TAF with VFR conds expected.
06/213 PM.
Winds and seas are expected to remain below Small Craft Advisory (SCA) criteria into this weekend, with the exception of northwest winds locally gusting to 20-25 knots in typically windy areas around and to the south of Point Conception each afternoon and evening through Saturday.
Dense fog may affect portions of the coastal waters each night through morning, especially this weekend across the waters north and west of Point Conception.
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 344-345-353-375-376-378>380. (See LAXNPWLOX). PZ, NONE.
