Weather Service Report

FXUS66 KLOX 291145

445 AM PDT Mon May 29 2017

...Aviation discussion updated...


A weak upper level ridge will breakdown and give way to an upper
level trough across the region early this week and persisting 
over much of California through most of the week. Expect more 
widespread low clouds and fog with a few showers possible Monday 
and Wednesday in the mountains with patchy drizzle for a few
valley and foothill areas by mid week.



Synoptically, the weak upper ridge that was over much of 
California and Nevada will begin to push east ahead of an 
approaching deep upper trough associated with a 542 DM low that 
will remain well north off the PAC NW coastal waters. There will 
be a couple weak disturbances within the upper flow that will 
bring a chance of showers to the SBA/VTU County mountains late 
this afternoon and across the northern slopes of the SBA/VTU 
county mountains on Wednesday with most the precip remaining well 
to the north and east. Expect high temps to trend a bit lower for 
most areas today and Tuesday. Then more significant cooling on 
Wednesday when high temps will be a few degrees cooler than normal
for this time of year. 

For this morning, low clouds have filled in nicely across the
Central Coast and Santa Ynez Valley. Low clouds have also started
to fill in across the LA and Ventura County Coastal areas and into
the San Gabriel Valley. Some high clouds were also moving through
the region as a very weak frontal boundary will bring some high 
clouds through the forecast area this morning. With the marine
layer now rising to around 1400 ft, expect low clouds to make it
into the San Fernando Valley and Ventura valleys as well before
sunrise.  Latest AMDAR sounding indicated the marine layer around
1000 ft deep this morning around LAX. As a weak Catalina Eddy 
gets going this morning, expect the marine layer to deepen to 
around 1400 ft this morning. With a relatively strong inversion 
in place, smokey conditions are likely to continue over the 
Mandeville Fire region today. Smoke will have a tough time mixing 
out until later this afternoon. People suffering from respiratory 
conditions should stay indoors until the smoke diminishes and 
mixes out late this afternoon. Low clouds could linger along a few
coastal areas into early this afternoon, thanks in part to the 
stronger inversion. 

The main issue for today will be the potential for a few elevated 
thunderstorms developing across the Ventura/Santa Barbara County 
Mtns later this afternoon. There is enough instability with 
limited mid level moisture to justify a slight chance for showers 
or thunderstorms. If storms do initiate, the main impact would be 
dry lightning, as well as strong downdraft winds when storms 
collapse. The San Gabriel Mountains should see some partly cloudy 
skies as there is less in the way of instability. 

Low clouds are expected to redevelop and push inland across coast
and valleys tonight into Tuesday morning. With little change
synoptically, expat for slightly stronger onshore flow, expect a 
degree or two of cooling across coastal areas, with little change 
inland. An upper disturbance will move through the upper trough on
Wednesday bringing a more significant deep marine layer. Some 
patchy drizzle has been added for the San Gabriel foothills. There
will be just enough lift with this trough that some showers will 
be possible across the northern slope of the SBA/VTU County 
mountains. Took out the chance for thunderstorms as the soundings 
looked quite anemic in respect to convection potential for 
Wednesday. High temps will bottom out on Wednesday with warmest 
valleys reaching the mid to upper 70s with a few locations 
reaching 80 degrees. Otherwise most areas will be the mid 60s to 
lower 80s across the Antelope Valley.


Both the GFS and ECMWF models are in fairly good agreement with 
large scale features through next weekend. After the trough axis 
moves through the region on Wednesday, broad NW flow aloft will 
occur on Thursday then by Friday a weak upper ridge will form over
southern California briefly. Expect a modest warming trend 
Thu/Fri across the entire region as heights and thickness lvls 
rise. Onshore flow will weak late this week, but there should 
continue to be night through morning low clouds. A weak upper low 
will build in from the SW over the weekend which will help to 
increase low clouds and begin another modest cooling trend. Models
seem to have a tough time dealing with systems coming up from the
SW. Will continue to go with cooler solution for the weekend.



At 09z at KLAX... The inversion was based near 1100 feet. The top
of the inversion was near 4100 feet with a temperature of about 
21 degrees Celsius. 

Overall... Moderate confidence in the current TAFs. LIFR/IFR 
conditions at most coastal locations will clear by 20z. There is 
a forty percent chance of LIFR/IFR conditions at KBUR and KVNY
through 18z and a thirty percent chance at KPRB and KSBA through 
17z. LIFR/IFR conditions will likely develop at coastal and 
adjacent valley locations after 30/08z. Otherwise and elsewhere 
VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. LIFR/IFR
conditions will clear by 20z then return again around 30/09z. 
Otherwise VFR conditions will prevail. No east winds above 7 knots
are expected.

KBUR... Moderate confidence the current TAF. There is a forty 
percent chance of LIFR/IFR conditions through 18z. Otherwise VFR 
conditions will prevail.


.MARINE...29/200 AM

Small Craft Advisory (SCA) conditions continue across the Outer 
Waters and in the nearshore waters of the Central Coast into at 
least Wednesday. There will be periods during overnight and early
morning hours when winds dip below SCA levels. 

The stronger winds will spill into the western half of the Santa 
Barbara Channel each evening but not far enough to warrant a SCA 
for the entire channel.

The winds peak Monday and Tuesday and there is a thirty percent 
chance that Gale conditions will form beyond 30 nm of the Central

The elevated winds will create a short period chop over all 
waters including the Santa Barbara Channel and Santa Monica Basin 
in the Inner Waters.


PZ...Small Craft Advisory in effect until 9 AM PDT Wednesday for
      zones 645-670-673-676. (See LAXMWWLOX).


No significant hazards expected.



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