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fxus66 klox 200539 
afdlox 


Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
939 PM PST Wednesday Nov 19 2008 


Update...high level moisture moving over the area will make for a 
difficult marine layer forecast tonight. Dense fog issues could 
likely be kept to a minimum tonight...but with marine inversion so 
thin and surface gradients so weak...patchy dense fog seems to 
make sense with the current package. For the current time...it is 
likely that dense fog advisories may not be needed tonight. 
However...marine layer is still expected to be an issue 
tonight...but it will remain difficult to forecast as high level 
moisture will likely obscure the patches of stratus. It is 
possible that some valley areas could see the marine layer creep 
in late...especially the Santa Ynez and San Gabriel valleys. 


Ksba-ksmx gradients have surged to 4.1 mb out of the north...and 
some sites are gusting into the 30s with Las Flores Canyon 
sustained winds around 30 miles per hour. An advisory has been issued for 
southern Santa Barbara County. The end timing of the advisory was 
a concern as NAM-WRF surface gradients are underdone tonight...and 
are not very reliable. Climatology would suggest an ending time 
around midnight...however...with NAM-WRF indicating the strongest 
thermal gradients at 09z...and another maxima at 15z. The advisory 
was extended until 8 am...or 16z. Boundary layer winds also peak 
at 09z as well. 


A dry boundary pushing south down the state currently will arrive 
over the area on Thursday afternoon. With 10 degree thermal 
gradients developing between the San Joaquin Valley and the Santa 
Barbara Channel...and the coldest air pushing into the northeast 
slopes of the Santa Barbara County mountains...it is likely the 
focus of the advisory level event will be placed on Santa Barbara 
County Thursday night and Friday. Some breezy conditions will 
likely occur in the I-5 corridor...but advisory level winds will 
probably not develop through I-5 corridor. It is likely that some 
advisory level gusts will occur on Whitaker Peak though. Some 
concern based on thermal pattern that the Santa Ynez Valley may be 
affected...and winds will likely have to be bumped up for this 
area. 


&& 


Previous discussion... /issued 200 PM PST Wednesday Nov 19 2008/ 


Short term (today-saturday)... 
temperatures down across the board today...as ridge continues to move to 
the east and grads slowly trend onshore. The biggest cooling has 
been realized along the coast thanks to a greater marine layer 
presence. Temperatures along the coast are trending 6-15 degrees cooler 
than yesterday. Elsewhere...temperatures are down on the order of 2-6 
degrees. Although it did break up nicely today...expecting an even 
greater stratus coverage tonight into tomorrow as onshore grads 
increase. Dense fog will be a concern again and advisories may be 
required again. Inland areas should see the most significant drop in 
temperatures on Thursday thanks to the lessening influence of the ridge to the 
east and greater onshore/marine flow. 


A weak and dry front still looks to pass over the area Thursday/Thursday 
night...which when coupled with a building surface high behind 
it...will bring significant northerly winds. Lax-bfl gradient looks to 
peak at a healthy -7.0 mb late Thursday night. An advisory level 
sundowner over sba County remains in the cards as a result...which 
will be more of a north-northeasterly variety and should 
unfortunately impact the Montecito area. These winds will not be 
nearly as strong as what occurred this last weekend...but will 
create heightened fire weather concerns...and a Fire Weather Watch will 
continue to address that. This tight gradient will also produce 
gusty northerly flow over the mountains of la/vtu County...especially the 
I-5 corridor...which may require an advisory. 


This flow will shift northeasterly late Friday morning. This wind 
should clear out any stratus and allow temperatures to warm up a bit...but 
not too much as general troughiness is expected at the upper levels. 
The central coast will likely see the biggest temperature boost and some 
local breezies. The one last wrinkle is that there is some moisture 
embedded in this flow...which may cause some clouds/fog to form on 
the north facing slopes and the far interior portions of sba/slow 
counties. Although some locally breezy northeast conditions will 
continue into Sat over la/vtu County...it will generally not be more 
than the 15 to 25 miles per hour variety. This will help to keep things above 
normal temp-wise...and keep things mostly clear...other than some 
lingering cirrus. 


Long term (sunday-wednesday)... 
generally light offshore flow is expected through Monday...as a series 
of weak-moderate surface highs form over Idaho and Utah. The models 
continue to struggle with the timing of the strength of the surface 
high...but they are all now saying that this will not be much of a 
wind event. With the trough aloft as well...not only will upper 
level support be in the wrong direction...but temperatures will not nearly 
be as warm as what occurred this last weekend. Generally 70s temperatures 
will be the common place. 


Tuesday and Wednesday still continues to be tough to nail down...but both the 
European model (ecmwf) and the GFS show an amplified trough moving over the Pacific 
which could produce some precipitation over California. We will continue to watch 
this with eager anticipation...but with the large spread in the 
ensembles and the models bouncing all over the place run-to-run...at 
this point cannot in good conscience go with more than 10 probability of precipitation and 
partly cloudies for the middle of next week. 


&& 


Aviation...20/0009z. 
VFR conditions are expected to persist at all inland terminals 
except kprb. There is a slight chance of MVFR conditions developing 
between 11z and 16z at kbur and kvny. At coastal terminals and 
kprb...some concern exists that increasing high level moisture may 
limit LIFR to IFR conditions tonight. It is possible that only MVFR 
conditions may develop. Timing of LIFR to IFR conditions should 
occur after 09z...but with lower confidence of IFR conditions 
developing. Package may be updated later to improve conditions. 


Klax...VFR conditions should occur through at least 04z...with IFR 
to MVFR conditions developing after 04z...or as late as 09z. Low 
confidence exists with LIFR conditions developing around 11z as high 
level moisture could keep conditions in the MVFR range throughout 
tonight and into Thursday afternoon. 


Kbur...VFR conditions are expected throughout the period except for 
a 20 percent chance of MVFR conditions developing between 11z and 
16z. 


&& 


Lox watches/warnings/advisories... 
Wind Advisory (see laxnpwlox). 
Fire Weather Watch (see laxrfwlox). 
Small Craft Advisory (see laxmwwlox). 
Gale Warning (see laxmwwlox). 


&& 


$$ 


Hall/kittell 


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