07/209 AM.
Night through morning low clouds and patchy 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, with near to above normal temperatures across the coasts and coastal valleys. Aside from the chance of a few mountain showers during the afternoon and evening hours through Sunday, dry conditions will prevail.
(tdy-Sun), 07/254 AM.
As has been the story for the last several weeks, a large and wide ridge of high pressure continues to remain centered over the four corners region through the short term period. 500 mb heights will increase from 593 dam to 596 dam through Sunday, bringing gradual warming, with the heat likely peaking on Saturday. High temperatures will be in 95 to 108 range for the interior areas (including the lower mountains/foothills), 90 to 100 across the coastal valleys, and 75 to 90 across the coasts/inland coasts. Less confidence in the coastal area temperatures due to slight variations in the onshore flow and marine layer clouds - if the night through morning clouds become more expansive, then temperatures across the coastal area may be on the cooler end of the range (and vice versa) Heat Advisories and Extreme Heat Warnings remain in effect for the interior mountains (including the foothills) and interior Valleys (such as the Antelope Valley and Cuyama Valley). Even through the coastal valleys are not included in these advisories, residents will need to be mindful of the afternoon heat and take appropriate precautions.
Monsoonal moisture will continue 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, and precipitable water values (PWs) of 1.0 inch to near 1.25 inches. Additionally, an upper level disturbance currently over the southern California Border today (where it is currently producing thunderstorms), will start to move northward over the region through Saturday, while weakening. This upper level disturbance will bring some instability over the region and pair with the monsoonal moisture to bring a 10-15% chance of afternoon/evening convective showers or thunderstorms through the weekend, mainly across the mountains of Los Angeles and Ventura Counties today, expanding into the Santa Barbara County Mountains on Saturday. 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 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.
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 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.
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), 07/257 AM.
The aforementioned ridge of high pressure will start to finally weaken over the area on Monday as a series of upper level troughs move into the Pacific Northwest down into NorCal. 500 mb heights will drop to at least 592 dam Monday through Thursday, 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 Monday through Thursday. Max temps will approach normals on Tuesday and then most areas will see below normal max temps on Wednesday and Thursday, with valley temps in the mid 80s to lower 90s.
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 stickier 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.
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.
07/0518z.
At 0418Z at KLAX, the marine layer was 1100 feet deep. The top of the inversion was at 2400 feet with a temperature of 25 C.
High confidence in VFR 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 TAF. Intermittent CIGs likely through early morning (009-012). No significant east wind component expected.
KBUR, High confidence in VFR TAF. No wind issues expected.
07/1257 AM.
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. There is a 20-30% chance of SCA level NW winds across the outer waters northwest of the Channel Islands Sunday afternoon into early Monday morning.
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.
