Scientific Forecaster Discussion
Southwest California area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
820 PM PDT Sat Oct 25 2014
..updated marine discussion...
Upslope flow and residual moisture will bring a slight chance of
showers to the northern mountain slopes into Sunday morning. Gusty
northwest to north winds can be expected at times tonight through
early Monday in the Santa Ynez Mountains and through the Interstate
5 corridor. Temperatures will be cooler through early next week. An
upper level ridge of high pressure will build in by Tuesday...with a
warming trend and above normal daytime temperatures through the
middle of next week.
Short term (today-tue)...evening update...
overall the forecast seem to work out in respect to the light
showers that occurred across the northwest portion of San Luis Obispo
County with less than a tenth of an inch reported. Hearst Castle
received around 0.07". The cold front had a rough time holding
together once it hit southern Monterey County as expected. High
temperatures were mostly in the lower to middle 70s for areas north of Point
Conception...and a good 6 to 10 degrees cooler in portions of la/vtu
counties. A few San Fernando Valley locations still made it into the
upper 80s which was a bit of a surprise...while most other areas
were in the middle 70s to middle 80s. There were some local gusty west
winds across the Ventura County coast and la County coast earlier
this evening but have sinced quieted down.
For this evening...latest fog product imagery indicated mostly clear
skies...except for some northerly moist flow across the San Joaquin
Valley was beginning to bank up some lower level clouds across
slo/sba County mountains. Expect that the Ventura/ western la County
mountains will also be affected with clouds building along the
northern slopes later tonight into Sunday. There will be a slight
chance of a few light showers across that area tonight into Sunday.
With the front pushing east of the forecast area...only expecting a
few stratocu buildups to move across areas north of Point Conception.
But a westerly jet moving towards socal will generate some enhanced
high level clouds across la/vtu counties later this evening. Latest
acars sounding near lax indicated the marine layer was around 700 feet
deep with a moderately strong inversion. There should be some
stratus developing overnight across the coastal waters of Los
Angeles County which should push across some low clouds over the
Los Angeles County coast and possibly the coastal valleys after
midnight as the inversion weakens due to the cooler air aloft moving
over the area. For Sunday...except for a few lingering clouds around
the mountains and foothills..skies should remain mostly clear. A few
degrees of cooling is likely as cooler air behind the front moves
across the entire region. Expect high temperatures to be in the middle 70s
with a few valley locations reaching the upper 70s. Should be a very
nice day tomorrow. By late Sunday afternoon...the northerly
gradients such as lax-bfl and sba-smx will strengthen causing local
gusty northerly winds across the I-5 corridor and sundowner winds
to develop. Winds should stay just below Wind Advisory thresholds
for these areas...but later shifts will monitor and adjust the
forecast if needed. By Monday morning...the GFS is showing a weak
kink in the broad northwest flow aloft which could bring a few clouds to
the forecast area in the morning...but 500 mb heights will be on the
rise. Also...at the lower levels...some weak offshore flow is
expected which should cause temperatures to rise modestly.
***From previous discussion***
With continued weak offshore flow on Tuesday and high pressure
starting to develop aloft...more noticeable warming is likely for
Tuesday. Highs Tuesday should climb back into the low 80s for the
valleys and middle 70s for the coast. Skies should remain mostly clear
Tuesday as well...with the weak offshore flow.
Long term (wed-sat)...
The warming trend and mostly clear skies will likely continue
through Wednesday with weak offshore flow during the morning hours
and high pressure continuing to build. Expect highs in the middle-upper
80s for the valleys on Wednesday and near 80 for the coast. Slight
cooling is likely for Thursday as offshore flow weakens and the
upper-level ridge axis moves east of the area. The 12z GFS, ECMWF,
and Gem remain in fairly good agreement that a large trough will
approach the West Coast on Friday or Saturday...bringing the
possibility of some rain to most of the area. For now...played it
safe and added a slight chance of showers north of pt Conception for
late Friday and Saturday...although if the current model projections
come true...Ventura and la County would see some light rainfall
amounts as well.
The base of the inversion at klax at 1655z was near 700 feet. The
inversion top was at 1600 feet with a temperature of 22 degrees c.
North of Point Conception...a weak cold front was moving through the
area with only isolated light showers across the NE portion of slo
County. Shower chances will end by 03z. After 03z VFR conds expected
to prevail except for kprb where MVFR ceilings may develop again late
South of Point Conception...for this evening...VFR conds should
prevail with a few high clouds and no chance of showers...except
northern slopes of la/vtu County mountains however...moderate confidence
in the return of some MVFR/IFR ceilings to lax basin taf sites after 08z.
Klax...high confidence in 00z taf through 06z with VFR conds after
06z...lower confidence in return of stratus ceilings with timing and
height of ceilings uncertain.
Kbur...moderate confidence in 00z taf. VFR conds through this
evening. After 06z...low confidence in forecast of stratus clouds
forming. 40% chance no low ceilings will develop and timing/height of
ceilings is uncertain.
High confidence in northwest winds increasing across the outer
waters tonight...with gale force gusts likely by Sunday afternoon.
The highest confidence in gales is over the waters from pt
Conception to San Nicolas Island...where gusts of 35 to 40 knots are
expected. In addition...a large moderate period west-northwest swell will
move into the waters this evening...with seas over the outer waters
rising to 10 to 13 feet at 13 seconds tonight into Sunday. Rough
seas are certain due to the combination of larger west swell and
northwest wind waves. Winds will diminish some by Monday
morning...but solid small craft winds are likely to persist over the
outer waters through Tuesday...with gale force gusts possible again
Inner waters...large seas are expected in the near-shore waters
north of pt sal...and a small craft for hazardous seas is in effect
this evening through Sunday. Hazardous bar conditions will be
possible at the Morro Bay entrance late tonight. The southern inner
waters will have local Small Craft Advisory gusts to 25 knots this evening...with
combined seas peaking near 5 to 8 feet Sunday. There is a 40% chance
that gusts will become widespread enough over the western portion of
pzz650 and pzz655 to require issuance of a Small Craft Advisory
Gale Warning (see laxmwwlox).
Small Craft Advisory (see laxmwwlox).
High surf advisory (see laxcfwlox).
High rip current risk (see laxsrflox).
Beach hazards statement (see laxcfwlox).