FXUS66 KLOX 271004
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
304 AM PDT Tue Jun 27 2017
High pressure aloft over the region will weaken over the next
several days as an upper-level trough over the Pacific Northwest
brushes the area. A cooling trend will develop through Thursday as
onshore flow strengthens and the marine layer deepens. A more
persistent stratus deck will become a staple of the weather
pattern for the coastal and valley areas through Thursday,
possibly lingering at the beaches throughout each day.
Skies are clear south of Point Conception but marine layer stratus
has filled the Central Coast and the Santa Ynez vly. Flat flow
across the state as a Pac NW trof has pushed the ridge down to the
south. 588 DM hgts will keep max temps 3 to 6 degrees above normal
across the vlys and inland areas while the coastal areas will be
right at normal. An enhanced thermal gradient will bring stronger
than normal westerly sea breezes to the area this afternoon and
There will be a little sundowner tonight. It will likely not
produce advisory level gusts. It will keep the stratus away from
the south coast. The rest of the coasts and lower coastal vlys
will see stratus clouds as the result of a decent sized eddy
There will not be too much change over the course of Wed and Thu.
At the upper levels the flat flow will turn anti cyclonic as a
small east pac ridge moves closer to the coast. This will create a
few degrees of warming across the interior on Thursday. The strong
onshore gradient will combine with the eddy to bring low clouds to
all the coasts and most of the vlys. There will be a strong
onshore push both Wed and Thu and this will produce slower than
normal clearing across the coasts and vly and no clearing at the
beaches. The clouds and enhanced sea breeze will lead to two days
of blo normal max temps for the coasts and vlys.
The little ridge peaks Friday morning and then is knocked down by
a little upper trof which will move through and then exit the area
later Saturday afternoon. Weak ill defined flow then sets up over
the state and the jet stream moves north.
Look for a little warming Friday then a little cooling on Saturday
and then two days of persistence Sun and Mon with max temps right
The night through morning low cloud pattern will persist through
the period as the onshore flow will continue through the period.
The only question mark is how much penetration it will have. The
hgts are rather high and this might limit the inland penetration
of the low clouds.
At 01000Z, the marine inversion at KLAX was based near 500 feet.
The top of the inversion was 2100 feet with a temperature of
29 degrees Celsius.
Overall, moderate confidence in 12Z TAF package. Current LIFR
conditions at KSMX/KSBP should dissipate by 17Z with VFR
conditions for all sites this afternoon. For tonight, high
confidence in return of stratus/fog to KSMX/KSBP, but only
moderate confidence in timing. For sites south of Point
Conception, moderate confidence in return of IFR conditions to
coastal TAF sites, but low confidence in timing (could be
+/- 3 hours of current forecasted arrival time).
KLAX...moderate confidence in 12Z TAF. High confidence in VFR
through this evening. For tonight, moderate confidence in return
of IFR conditions, but low confidence in timing (+/- 3 hours of
current 08Z forecast).
KBUR...high confidence in 12Z TAF. There is a 10-15% chance of
MVFR VSBYs after 10Z.
For the Outer Waters, high confidence in current forecast.
Northwest winds will remain at Small Craft Advisory (SCA) levels
through Saturday, generating short period seas.
For the Inner Waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, high confidence in
SCA level winds developing each afternoon/evening today through
Saturday. For the waters south of Point Conception, moderate
confidence in SCA level winds across the western half of the Santa
Barbara Channel this afternoon and evening. Otherwise, winds and
seas are expected to remain below SCA levels through Saturday.
Several small fire starts across the forecast area today as gusty
onshore winds coupled with continued hot and dry conditions across
inland areas. A large fire called the Hill Fire in SLO County
(located to the east of Santa Margarita) has spread rapidly to
900 acres as of 8 pm. Gusty onshore winds will continue to spread
the fire and smoke plume eastward this evening. The low level
winds in this area will diminish overnight then shift to a light
north to northeast direction on Tuesday morning. Elevated fire
weather concerns will then return to the fire area on Tuesday
afternoon as gusty onshore winds combine with very warm and dry
conditions in the afternoon and evening hours. The 00z Vandenberg
sounding showing the marine layer depth around 1100 feet, with
marine layer clouds not expected to reach the fire location
Red flag conditions observed today across portions of the Antelope
Valley, LA county mountains, and Santa Clarita Valley. Current Red
Flag Warnings for those areas are set to expire at 9 pm, which
looks on track as onshore winds will continue to slowly diminish
tonight. Despite the diminishing winds, there will be poor
humidity recoveries tonight across the mountains and foothills.
Other area of concern is gusty sundowner winds this evening and
again Tuesday evening across the portions of the Santa Ynez
mountains and SBA south coast, especially from Gaviota to Goleta.
As of 8 pm, SBA-SMX gradient was at -4.4 mb. With not much in the
way of upper level wind support, looking for localized wind gusts
in the 35 to 40 mph range. These winds coupled with warm/dry
conditions will bring elevated fire danger over that area this
evening and again Tuesday evening. As of 8 pm, Montecito Hills
reporting north winds gusting to 26 mph with a temperature of 90
degrees and humidity of 10 percent.
Fire weather conditions improve a bit Tuesday all areas with the
upper level ridge beginning to weaken, bringing cooler
temperatures and slightly higher minimum relative humidities. The
single digit relative humidities will be restricted to far eastern
Antelope Valley, although min RH's in the lower teens will
reappear across all interior sections. Winds, however, will not
be as strong as today's, but still breezy in spots in the
afternoon to warrant elevated fire weather conditions.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
AM PDT Wednesday for zone 645. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Wednesday for
zones 650-670-673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK...(THU-MON)
No significant hazards expected.
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