23/839 AM.
Strong onshore flow and a deep marine layer will bring low clouds and patchy fog and drizzle to the coast and coastal valleys throughout this week with partial afternoon clearing. Cool conditions will continue, with high temperatures several degrees below normal each day this week. A couple of weather disturbances will track across the area as well, bringing a small chance for drizzle or light rain showers. Warmer weather is expected by the weekend.
(tdy-Thu), 23/851 AM.
***UPDATE***
Pilot reports and soundings are indicating the marine layer depth has reached a remarkable 5000 feet today. Meanwhile, onshore gradients to the east have risen to 6mb. So it's going to be another cool day across the area. However, satellite imagery is showing quite a bit of thinning of the cloud layer with numerous breaks in the overcast so it appears likely that many areas will see a fair amount of sunshine by afternoon, if not sooner. That alone should bring temperatures up a few degrees, but still well below normal. In these deep marine layer patterns often the clearing pattern is best described as going in reverse, meaning it clears near and over the ocean first, then works its way inland through the afternoon, but it doesn't always make it all the way. So inland areas, particularly near the south facing mountains, will have a harder time clearing.
Despite the likely appearance of sunshine today, the overall pattern for the week remains cool with lots of marine layer stratus. There remains at least a 20-30% chance of drizzle or light rain at times. Best chances for that would appear to be late Wednesday into Thursday when the primary trough moves through the area.
***From Previous Discussion***
Tonight and Wednesday will not look too much different from today as all most all weather parameters look similar. There is a little less onshore flow to the north so its possible that some inland vlys like Ojai and Santa Clarita will see earlier or better clearing.
On Thursday a weak trof will move through the state. By itself this trof will not produce rain, but when it interacts with and lifts the marine layer it could produce some light rain esp near the foothills. More likely it will just produce more drizzle - either way many people will likely need their wipers during the morning commute. There is a smaller chance the the capping inversion will be lifted and mixed out which will cause most of the low clouds to simply dissipate. The marine layer clouds should dissipate in the afternoon in the wake of trod as cooler and mixing should eliminate the marine clouds. The return of afternoon sunshine should overwhelm the limited cool air advection behind the trof and max temps should rise 2 to 5 degrees across most locations. Max temps will still end up 5 to 10 degrees blo normal with max temps across the csts/vlys only in the 60s.
(Fri-Mon), 23/319 AM.
Low confidence in the Friday morning fcst. There is a good chance that the marine inversion will not reform and skies will be mostly clear. But there is a second little piece of energy coming in over the area and the ensembles are trending to another round of low clouds and perhaps some more drizzle. Still the mdls seem to be trending towards a less dynamic system and would not be surprised to see this fcst change. Better confidence in 2 to 3 degrees of warming with ample afternoon sunshine and rising hgts.
Then just in time for the weekend a ridge arrives along with weaker onshore flow or evening weak offshore flow. There will be only limited marine layer clouds and warming each day Saturday through Monday. A few sites will see above normal temps on Sunday and many locations will be above normal on Monday when max temps will mostly be in the 70s and lower 80s across the csts and vlys.
23/1045z.
At 1030Z, the marine inversion at KLAX was based at 3500 feet. The top of the inversion was 4800 feet with a temperature of 12 degrees Celsius.
Overall for 12Z TAF package, low to moderate confidence for coastal/valley TAFs and high confidence for desert TAFs. Lower confidence for coastal/valley sites due to uncertainties in timing of flight category changes. There is a 40% chance of some afternoon clearing at sites with no clearing forecast and also a 40% chance of no afternoon clearing at sites with a clearing forecast.
KLAX, Moderate confidence in 12Z TAF. There is a 40% chance of IFR CIGs 12Z-17Z. There is a 30-40% chance that MVFR CIGs will dissipate 20Z-04Z. No significant easterly wind component is expected.
KBUR, Moderate confidence in 12Z TAF. There is a 40% chance of IFR CIGs 12Z-17Z. There is a 30% chance that MVFR CIGs will not dissipate this afternoon.
23/845 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Wednesday night, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. For Thursday through Saturday, high confidence in combination of SCA level winds and seas. Across PZZ673/676, there is a 40-50% chance of Gale force winds Thursday afternoon/night and a 20-30% chance Friday afternoon/night.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Wednesday night, high confidence in winds and seas remaining below SCA levels. For Thursday through Friday, there is a 60-80% chance of SCA level winds, especially in the afternoon and evening hours. On Saturday, there is a 40-50% chance of SCA level winds, especially in the afternoon and evening hours.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through Wednesday night, high confidence in winds and seas remaining below SCA levels. For Thursday through Saturday, there is a 60-80% chance of SCA level winds with the strongest winds across western sections.
Ca, NONE. PZ, NONE.
