Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
1100 am PDT Thursday may 23 2013
..updated aviation discussion...
Synopsis...
Gusty northwest winds will continue today across the
mountains...deserts...and portions of the central coast. An area of
low pressure will linger over the western United States through
early next week with areas of night through morning low clouds and
fog. Temperatures will stay below normal through early next
week...then a warming trend should begin by midweek.
&&
Update...
no significant changes to the forecast this morning. Low clouds were
across valleys and coasts of Ventura and Los Angeles counties with
the marine inversion exceeding 4k feet. A couple of sprinkles have
been reported as the clouds lift...but expect continued thinning and
decrease in cloud cover today. Just a few minimal spots of clouds
along the west Santa Barbara coast this morning. Virtually all areas
are running 2-6 degrees cooler than yesterday with 6-10 degrees
cooler across the mountains.
Other story today are the gusty west to northwest winds. Already
gusting to 40 miles per hour across the western av and picking up in the
Lancaster area. Onshore pressure gradients slightly stronger at 16z
compared to yesterday...but model gradients peak at a lower value
today or about 1mb less. Will let all advisories continue as
planned...including the central coast.
First look at marine inversion forecast for Friday morning. WRF
gradient forecasts have been rather poor and missed this morning by
over 3mb...so little confidence in the very weak onshore gradient
for tomorrow. Catalina eddy looks weaker for Friday and 30agl
humidities are less organized but I don't see much mechanism to
reduce the overall marine layer. Will play up similar areas for
clouds in the morning. Likely to see a little deepening of the
marine layer for Saturday.
***From previous discussion***
Long term (sun-wed)...
models agree that on Sunday and Monday the upper low will open up into
a trough and move slightly to the south. Models indicate that the
onshore flow will also decrease and this should be the bigger
weather factor. The decrease in onshore flow will allow earlier
clearing and a few degrees of warming across the coasts and valleys.
Desert and mountain temperatures will likely not change much.
The Tuesday Wednesday forecast is a little murkier. Both models push the
trough southward but the GFS is much faster and the ec is slower the
ec in fact brings 24 hours of light rain to the area. This is a
little extreme especially for this time of the year. Ramped up the clouds
and cooled temperatures some but need to see some model run to run constancy
before jumping on the rain bandwagon.
&&
Aviation...23/1800z.
Persistence forecast will keep a deep and rather weak marine layer
over the area. MVFR to VFR ceilings over koxr and the la coast and
valley sites will dissipate from 18z-20z today...although timing may
differ by +/- 1 hour.
North of pt Conception there is a 20% chance that MVFR ceilings will affect
ksmx overnight.
S of pt Conception expect MVFR ceilings to reform over koxr and la coast
and valley sites...but the timing may differ +/- 2 hours from taf
times. 10% chance that any of these sites will see VFR ceilings form
overnight...or that only scattered lower clouds will develop.
Periods of moderate to occasionally strong low-level wind shear and
turbulence is possible at ksba after 23z.
Klax...moderate to high confidence in 18z tafs. Broken VFR ceilings will
scatter out through 20z. MVFR ceilings will return by 08z...with a 30%
chance that timing will differ +/- 2 hours from taf times.
Kbur...moderate confidence in 18z tafs. Broken VFR ceilings will scatter
out through 22z. There is a 30% chance that VFR conds will continue
through the overnight period. Otherwise MVFR ceilings are expected after
09z...but timing could differ +/- 2 hours from taf times
&&
Lox watches/warnings/advisories...
Wind Advisory (see laxnpwlox).
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).
&&
$$
Public...boldt/rorke
aviation...Smith
synopsis...seto
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