Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southwest California area forecast discussion 
National Weather Service Los Angeles/Oxnard California
125 PM PDT Friday Aug 29 2014

Synopsis...

Above normal temperatures are expected across the region through
Saturday due to lingering high pressure. Gusty sundowner winds are
expected at times through Saturday night as well. A weak trough of
low pressure and increasing onshore flow will then bring gradual
cooling to the region through middle week...along with increasing night
through morning clouds for the coastal and valley areas.

&&

Short term (today-mon)...

Water vapor imagery this afternoon shows an upper level trough
entering the Pacific northwest and a ridge of high pressure remaining over
Southern California. Visible satellite imagery also shows low clouds
hugging the central coast this afternoon...probably due to a
relatively sharp inversion near about 1800 feet.

The main forecast concern in the short term will be gusty sundowner
winds over the next several nights...as the aforementioned upper
level trough pushes through the area later tonight. Winds through
the Santa Ynez range...I-5 corridor and Antelope Valley are expected
to remain below advisory levels through tomorrow morning...as winds
will be primarily driven by surface pressure gradients...with the
upper-level ridge remaining in place. The sba-smx gradient is
expected to reach about -3.0 to -3.5 mb later this evening. Tomorrow
evening...the NAM projects a sba-smx gradient of about -4.0
mb...along with an increase northwest flow aloft. As a result...advisory
level sundowner winds seem like a good possibility along the Santa
Ynez range late tomorrow afternoon and tomorrow night...with
advisory level winds also possible for the I-5 corridor and the
Antelope Valley. Low relative humidity along with the gusty winds will bring
elevated fire weather concerns to some of these areas as well (see
fire weather section below).

Inland areas will remain quite warm through the weekend as height
and thickness values do not change much despite the trough pushing
the center upper level ridge to the south. Expect high temperatures around
100 for the hottest valley locations on Saturday with a couple of
degrees cooling possible by Sunday. Coastal areas should see a few
degrees cooling over the next couple of days as onshore flow will
increase slightly. The exception will be the sba South Coast...where
warmer conditions are expected due to the sundowner winds.
Increasing northwest flow across the coastal waters will also help the
Catalina eddy to spin up late tonight and again tomorrow night. This
should deepen the marine layer south of Point Conception a
bit...also helping with slightly cooler conditions for the la and
Ventura coasts over the weekend. Low clouds will likely return to
the la coast...and possibly the Ventura coast over the weekend. The
gradual cooling trend will continue into Labor Day...as height and
thickness values continue to fall.

Long term (tue-fri)...

Long range models are in pretty good synoptic agreement overall.
Tuesday through Thursday...the upper level flow transitions to the
SW as a weak upper level low develops off the northern California coast.
This should result in continued cooling...with below normal
temperatures for most areas by middle week. A deepening marine layer
and an increase in marine layer cloud coverage through middle week
seems like a good bet as well. Little change expected for the end of
the week...as the upper low stalls out off the northern California coast.

&&

Aviation...29/1725z...

Overall...moderate confidence in 18z taf package. VFR conds expected
all sites through early this evening. For tonight...IFR/LIFR ceilings
expected to return to central coast and Salinas valley. For areas
south of Point Conception...weak eddy may spin up tonight...with IFR
ceilings developing at klgb/klax and even potentially pushing up to koxr
late tonight.

Klax...moderate confidence in 18z taf. Timing of IFR ceiling return
tonight could be +/- 3 hours of current 08z forecast.

Kbur...high confidence in 18z taf. There is a 10% chance of IFR/LIFR
ceilings during the 10z-16z time period.

&&

Marine...29/100 PM...

For the outer waters...high confidence in the development of Small
Craft Advisory-level northwest winds this afternoon...and continuing
through Sunday. Low to moderate confidence in the development of
widespread gale force wind gusts Saturday afternoon/night. So...will
continue with the gale watch with the afternoon forecast...and let
future shifts see how things develop with respect to gale
conditions.

For the inner waters...moderate confidence in northwest winds
reaching Small Craft Advisory levels across the western half of the
Santa Barbara Channel potential this afternoon and tonight. For
Saturday afternoon and evening...higher confidence for Small Craft
Advisory level winds across the western half of The Channel.
Elsewhere across the inner waters...winds are anticipated to remain
below Small Craft Advisory levels through the weekend.

&&

Beaches...29/100 PM...

Based on the latest coastal observations...surf conditions have
diminished below high surf advisory levels. Therefore...the
advisories have been cancelled.

Although the southerly swell...and resultant surf...will continue to
gradually diminish through the weekend...there will still be the
potential for rip currents along the local beaches this Holiday
weekend.

&&

Fire weather...29/1015 am.
Gusty sundowner winds are expected across the passes and
canyons of southern Santa Barbara County from the late afternoon
through nighttime hours through Saturday night. Wind gusts are
expected to range between 30 and 40 miles per hour with tonight's event...mostly
focused across western portions of the South Coast. Tomorrow night's
event is expected to be slightly stronger and more widespread. Wind
exposed locations and foothills will generally see humidities in the
teens with temperatures climbing to 90 degrees or above. The
combination of gusty sundowner winds...low humidities...and warm
temperatures will bring elevated fire danger to the Santa Barbara
South Coast and adjacent foothills through Saturday night...with
brief periods of critical fire weather conditions each night. Gusty
northwest winds and low humidities will also impact the Interstate 5
corridor of the Los Angeles County mountains and Antelope Valley
through Saturday night. The strongest winds for these areas are
expected late Saturday afternoon through Saturday night...when gusts
between 35 and 45 miles per hour can be expected.

&&

Lox watches/warnings/advisories...
Small Craft Advisory (see laxmwwlox).
High rip current risk (see laxsrflox).
Gale watch (see laxmwwlox).

&&

$$

Public...sukup
aviation/marine...rat
fire weather...gomberg
synopsis...seto

Www.Weather.Gov/losangeles

National Weather Service Glossary of Abbreviations