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Area forecast discussion...updated 
National Weather Service Los Angeles/Oxnard California
906 PM PDT Wednesday Jul 27 2016

Synopsis...

High pressure aloft will result in above normal temperatures
through the end of the week, with night through morning low clouds
and fog affecting some coastal areas. Temperatures will return to
near normal over the weekend and early next week as high pressure
weakens. Monsoonal moisture will bring a slight chance of
thunderstorms for the mountains and desert over the weekend.

&&

Update...

High pressure aloft remains anchored over southern Nevada this
evening. Southeast flow aloft around the high pressure center
continues to keep the door open for middle and high-level
moisture to stream into the area from the subtropics. With
precipitable water values over one inch and near 1.4 inches over
portions of the area, the moisture is already in place. Cumulus
build-ups occurred across the mountains and desert today and will
continue tomorrow. Model solutions are starting to hint at a bit
more instability for Thursday. Lifted index values are trending
more negative over the mountains and desert. With this in mind,
cloud cover will be increased over the mountains and desert
slightly but the tweak will not change the text forecast. The
next shift will be briefed about the possibility of a bit more
instability for Thursday and could introduce higher pops.

With surface pressure gradients trending onshore currently and
forecast to be more strongly onshore for slight cooling should
develop across the coast and valleys on Thursday. The forecast
presents a cooling trend currently and minimal changes are
planned.

&&

Previous discussion...

Short term...minimal changes to the forecast through Saturday.
Models continue to advertise a very slight warming trend through
Friday as the 4 corners high pressure ridges strengthens while
gradient trends remain basically flat. Just a degree or two at
most and mostly for areas away from the immediate coast. Marine
lyr will remain shallow but still pretty solid along much of the
coast during the overnight and early morning hours. Dense fog will
continue to pose some issues for coastal areas during those times
but should burn off fairly early each day.

Moisture continues to be a limiting factor with thunderstorm
formation the next few days. Some instability but too dry. By
Friday we start seeing a tad more moisture and instability but
agree with previous shift that chances seem too low to include in
the forecast. Somewhat better over the weekend, enough to tip the
scales into the slight chance category, but again moisture is
scant and mostly at or above 600mb. Perhaps more concern for dry
lightning and gusty winds.

Long term...ridge starts to weaken over the weekend allowing
temps to drop a few degrees, especially far inland areas like
Antelope Valley and interior slo County. However, marine lyr will
remain shallow and confined mainly to coastal areas. May have
slightly later burn off times but otherwise not much change. Will
continue to leave thunderstorms out of the forecast after Sunday,
though there are hints of additional moisture surges into southeast
California early next week so if thunderstorms do flare up over
the weekend pops may need to be added.



&&

Aviation...28/0000z.

At 00z, the marine layer was around 550 feet deep at klax. The
top of the inversion was near 2600 feet with a temperature around
28 degrees celsius. There was a subsidence inversion above the
marine inversion up to near 6200 feet.

LIFR to IFR conditions will likely spread into coastal terminals
through 11z. The highest likelihood on LIFR conditions exists for
coastal terminals north of koxr. Conditions should improve to VFR
between 15z and 19z.

Klax...there is a 80 percent chance of IFR conditions by 10z. VFR
conditions should redevelop between 16z and 18z.

Kbur...high confidence in VFR conditions throughout the period.

&&

Marine...27/900 PM.

High confidence in the current forecast through Friday. The
marine inversion remains shallow which will result in lingering
dense fog at times and poor visibilities across the outer waters,
near the northern Channel Islands, and in the Santa Barbara
Channel through at least Thursday morning. Weak to locally
moderate northwest winds will kick up each afternoon near the
islands and across the outer waters, with gusts up to 20 kts
through the early evening hours. A Small Craft Advisory was added
for Thursday afternoon and evening for the southern outer waters.
This advisory may need to be reissued for or extended into Friday
afternoon and evening across.

A continued south swell mixing with northwest swell is forecast
with the a longer period southerly swell arriving over the weekend
and lingering into early next week.



&&

Fire weather...27/200 PM.

Hot and dry conditions continued today with widespread temperatures
in the 90s and 100s across the interior and relative humidities in
the 10s to low 20s. A slight increase in onshore flow and
increasing north flow has resulted in winds starting early today
and about 5 mph stronger. These winds are expected to transition
to locally gusty northwest winds across the I-5 cooridor into the
western Antelope Valley tonight. Additionally, a weak Sundown
across the western Santa Barbara South Coast may bring northwest
wind gusts up to 25 mph tonight. A few degrees of warming with a 2
to 5 percent drop in minimum relative humidities is expected for
Thursday.

Elevated fire weather conditions across the interior mountains and
valleys including the location of the sand fire will persist each
afternoon and early evening through Thursday or Friday due to low
relative humidities and locally gusty onshore to northwest winds.
Northwest winds are expected to peak across the I-5 cooridor and
western Antelope Valley Thursday night with gusts up to 35 mph. A
weak to moderate sundowner is also possible Thursday evening for the
western Santa Barbara South Coast and the Santa Ynez range with
local wind gusts to 35 mph. Additionally, substantial drying aloft
may bring minimum relative humidities back down to 8 to 15 percent
to the interior mountains (also the Santa Ynez range) above about
2000 feet including far interior areas feet Thursday possibly
extending into Friday. This combination of low minimum relative
humidities and gusty winds across the I-5 corridor, western
Antelope Valley and western Santa Barbara South Coast may support
a few hours of critical conditions Thursday evening.

Elevated fire weather concerns extend into the upcoming weekend
due to the possibility of afternoon thunderstorms across interior
areas as high pressure weakens and shifts east, opening the door
for a push of monsoon moisture from the southeast.
&&

Lox watches/warnings/advisories...
California...none.
Pz...Small Craft Advisory in effect from 3 PM Thursday to 3 am PDT
Friday for zones 673-676. (See laxmwwlox).

&&

$$

Public...Hall
fire weather...Munroe
aviation...Hall
marine...Hall
synopsis...sukup

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