12/914 AM.
A gradual cooling trend is expected through Saturday as high pressure weakens. Areas of dense fog are possible near the coast. Temperatures will trend warmer again Sunday through the middle of next week before cooling returns the end of the week. The next chance of rain is during the week of Christmas.
(tdy-Sun), 12/316 AM.
We’re in for a relatively quiet mid-December through Sunday across Southwest California. The persistent ridge of high pressure responsible for the warm temperatures this week will weaken slightly today and Saturday while remaining stagnant Sunday. The continuous upper level ridging will allow for the warmer than normal and dry weather to continue, though high temperatures will be lower today and this weekend compared to Thursday. We’re looking at 2 to 5 degrees of cooling across most coastal areas as offshore flow dampens today. Highs in the low to mid 80’s will be common across most coastal valley areas, while the immediate coasts will top out in the low 70’s. A few more degrees of cooling will occur Saturday, especially for the Central Coast beaches and coastal valleys across all four counties. Most areas will top out in the 70’s, but warmer valleys will reach the low 80’s. Coasts will reach the upper 60’s to low 70’s. Very minimal changes between Saturday and Sunday. Low temperatures will be quite a bit cooler during the short term compared to this past week, especially across the coasts and areas impacted by the offshore winds.
The aforementioned decrease in offshore flow from the north and the east will continue into Saturday, where gradients will become near neutral Saturday morning through Sunday. Winds will likely flip to weakly onshore Saturday and Sunday afternoon.
Patchy marine layer clouds have developed south of Point Conception, and the very shallow marine layer depth has led to dense fog developing wherever clouds are present. Thus a Dense Fog Advisory has been issued through 10am for the southern Santa Barbara coast, Ventura immediate and inland coast, Malibu coast, LA immediate and inland coasts. Low clouds and fog are likely to become more widespread and filled in across coastal areas from San Luis Obispo County south to Los Angeles County during the night to morning hours this weekend.
(Mon-Thu), 12/316 AM.
We’re not out of the woods yet when it comes to the December warmth. The upper level ridge will build back up Monday through at least Tuesday. Offshore flow from the north will increase Monday and Tuesday, continuing through the period, but it is forecast to be weaker than this past week. The LAX-DAG gradient is forecast to turn back offshore during the same period, but also remain weaker than this past week. High temps are currently forecast to be 10 to 15 degrees above normal Monday and Tuesday, with isolated areas up to 20 degrees above normal.
There is some discrepancy between the GFS ensemble (GEFS) and EC ensemble (ENS) for the Wednesday through Thursday period. The ENS keeps the upper level ridge overhead through the period, while the GEFS turns the upper levels more zonal. The ENS does weaken the upper level ridge, but this solution would still result in some warmer temperatures through the week. The GFS turns the LAX-DAG gradient back onshore Wednesday while the EC keeps the weak offshore flow going, which will also result in cooler temperatures in the GFS scenario compared to the EC scenario. Went ahead and kept the NBM max temperatures for Wednesday and Thursday due to this discrepancy, but these temps are still likely to be too cool regardless of which scenario plays out.
12/1727z.
At 1704Z at KLAX, the marine layer was 300 feet deep. The top of the inversion was 1900 feet with a temperatures of 22 Celsius.
Overall, low to moderate confidence in 18Z TAF Package.
VFR conditions expected at desert airfields (KPMD & KWJF).
VLIFR or LIFR conditions will likely have more expansive coverage tonight into Saturday morning. Timing of CIG/VSBY restrictions may be off +/- 3 hours, and flight minimums off by one category. There is a 20% chance V/LIFR conds after 14Z Saturday at KPRB. Very low confidence if and when CIGs arrive at KSBP.
KLAX, Low to moderate confidence in TAF. Arrival and clearing times of CIGs may be off +/- 3 hours. Expecting longer coverage of V/LIFR conditions as early as late this afternoon through tomorrow morning. VV001-OVC004 with 1/4SM FG possible to likely at times. No significant east wind component expected through period.
KBUR, High confidence in VFR conditions through at least Saturday with light winds.
12/757 AM.
Areas of dense fog with very low visibility will affect the coastal waters through at least Saturday. This fog could form anywhere at anytime, with indications of it expanding in coverage through Saturday. While the focus will be in the overnight and morning hours, some pockets will likely through the afternoon and evening hours.
High confidence in unusually light winds and lowering seas through the weekend. More typically gusty NW-W winds will likely return, Monday and Tuesday. These winds will strengthen further Wednesday and Thursday, when there is a 30% chance for Gale Force winds from near Point Conception to San Nicolas Island including western and southern portions of the Santa Barbara Channel. These stronger winds will likely result in choppy seas.
Ca, Dense Fog Advisory remains in effect until 10 AM PST this morning for zones 350-362-366-368. (See LAXNPWLOX). PZ, NONE.
