Southwest California area forecast discussion National Weather Service Los Angeles/Oxnard California 1048 PM PDT Friday may 24 2013 ..updated aviation discussion... Synopsis... a low pressure area will continue through Tuesday bringing night through morning clouds and fog. Breezy conditions will occur in the mountains and deserts on Sunday and Memorial Day. There will be possible precipitation from Monday night to early Wednesday morning. The afternoon temperatures will remain below normal through Tuesday... then a warmup will start midweek with temperatures going above the seasonal normals by the weeks end. && Short term (tonight through monday)... satellite imagery showing mostly clear skies across the forecast area this evening. Persistent upper level trough along West Coast will deepen through the weekend across California. This will maintain a strong onshore flow pattern at the surface along with a deep marine layer. Latest acars sounding showing marine layer depth around 3000 feet...but the inversion is quite weak. While the latest 00z NAM model continues to show a good surge of low level moisture all the way to the lower coastal slopes...the big question mark is whether or not the inversion will be strong enough to form an organized area of low clouds. Will continue with current forecast bringing low clouds across much of Los Angeles and Ventura counties...possibly reaching the sba South Coast by morning. Also...expecting low clouds and fog to become more solid along the central coast as well overnight. With the marine layer expected to deepen slightly by morning...should see some low clouds and fog spread into the lower coastal slopes of the san Gabriels. By Saturday afternoon...skies should generally turn mostly sunny...however some low clouds will likely lingering across some immediate coastal areas. Continued mild temperatures through the Holiday weekend...with valleys generally remaining in the 70s. *** From previous discussion *** By Sunday...the marine layer looks to behave similarly to Saturday...but with a little deeper inland push thanks to stronger onshore gradients. By the afternoon however...increasing northwest flow will help to clear things out better...with nearly all areas clear by the afternoon. This flow will also result in some downslope warming...especially over southern sba County. The wind itself will flirt with advisories over the I-5 corridor and Santa Ynez range...but should stay below advisory thresholds. By Memorial Day Monday...the winds will be stronger...and advisories look likely by the late afternoon for the I-5 corridor...southern sba County...central coast...and Antelope Valley. This should significantly disrupt the marine layer...and bring a little warming to coastal areas. Mountains and northern areas however will be cooler...as the airmass cools in advance of an approaching upper level trough. Long term (monday night through friday)... the previously mentioned trough looks to have a frontal system that will sustain itself enough to bring chances of rain to our area. Being very unseasonable for almost June...the models are struggling on the track of the system. The European model (ecmwf) digs the core of the trough all the way into southeast California...while the GFS keeps it up in Nevada. While this difference adds a lot of uncertainty as to the amount of rain that could result from this...confidence is growing for at least some precipitation. With the flow staying northwesterly...the best chances are north of Point Conception and on the northern mountain slopes of la/vtu counties. At this point...the timing of any rain would be Monday night and Tuesday...but being so unseasonable...the timing will likely be tweaked over the next couple of days. If the European model (ecmwf) is correct...we could be looking at 0.1-0.5 inches of rain north of Point Conception...with 0.01-0.10 inches to the south. If the GFS pans out...north of Point Conception would see 0.01-0.10 inches...while other areas would be hard pressed for anything measurable. So at the end of the day...it isnt a lot of rain...but quite significant considering the time of the year. Temperatures will be down to no surprise on Tuesday with ample cloud cover. The marine layer should take a hit however...and Wednesday should be mostly stratus free. Temperatures will up a couple of degrees as a result...except over interior areas. Weak ridging should follow into the end of next week...with a re-establishment of the marine layer and associated low clouds and fog. Temperatures will go up away from the coast...as we should finally reach or exceed normals by Friday. Meanwhile...gusty but just sub-advisory northwesterly flow looks to persist...as is typical for this time of the year. && Aviation...25/0545z... Overall...low confidence in 06z taf package. Some patches of stratus are developing across the central coast...with clear skies elsewhere. The marine inversion is deep...but weak...so stratus will likely remain somewhat chaotic overnight. Did bring MVFR ceilings up to koxr overnight...but confidence in timing/areal coverage is low. Any stratus that develops should burn off rather quickly late Saturday morning. Klax...low confidence in 06z taf. Timing of stratus return may be +/- 2 hours of current 11z forecast...with a 30% chance that ceilings may not develop at all. Kbur...low confidence in 06z taf. Timing of stratus return may be +/- 2 hours of current 12z forecast. There is a 50% chance that MVFR ceilings will not develop. && Lox watches/warnings/advisories... gale watch (see laxmwwlox). Small Craft Advisory (see laxmwwlox). High rip current risk (see laxsrflox). && $$ Public...gomberg/kittell aviation...rat synopsis...seto Www.Weather.Gov/losangeles