Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 042100
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
200 PM PDT Thu Jun 4 2020

.SYNOPSIS...04/154 PM.

Temperatures will trend cooler into Sunday as an approaching low
pressure system brings clouds and cooler temperatures to the area.
There is a slight chance of afternoon thunderstorms across some
of the mountains and interior locations today with a better
chance on Friday. There will be gusty northerly winds are
over the weekend and into early next week across portions of the
area. Another warming trend is expected next week.

&&

.SHORT TERM (TDY-SUN)...04/153 PM.

Overall, 12Z models in good synoptic agreement with the short term
forecast. At upper levels, low, currently about 550 miles
southwest of LA, will gradually move northeastward across the area
on Friday then off to the east on Saturday with broad cyclonic
flow remaining Saturday/Sunday. Near the surface, moderate to
strong onshore flow will prevail into Saturday with some
northerly flow developing Saturday night and Sunday.

Forecast-wise, main issue in the short term is possible
convection over the mountains/interior sections through Friday.
Some moisture and instability is still in place over the mountains
this afternoon, currently generating some cumulus buildups. With
the balance of the afternoon ahead, there may be enough "oomph" to
generate an isolated thunderstorm over the mountains and interior
sections (mainly from Ventura county northward). Any storms that
develop today will produce little rain, with dry lightning strikes
and gusty outflow winds the main concerns. This afternoon will
diminish this evening, but the chances return on Friday as the
upper low moves overhead. Models more impressive with convective
parameters on Friday. NAM indicates lifted indices of -3 to -6 and
MUCAPE near 2000 over the mountains and interior sections while
the GFS is a bit less impressive (LI`s -2 to -4 and MUCAPE near
1300). With PWATs between 0.75 and 1.00 inches, decent possibility
of thunderstorm development Friday afternoon/evening. Will
indicate chance POPs over Ventura county mountains (location of
model bullseye) and slight chance POPs for LA/SBA/SLO mountains
and interior sections. With the better instability on Friday, any
storms that develop could generate more rainfall than previous
storms, but still gusty outflow winds and possible dry lightning
strikes.

Otherwise, forecast is pretty straightforward for early June.
With lowering H5 heights and good onshore flow, marine inversion
will deepen and stratus will push further inland. There may even
be some patchy drizzle/light marine layer showers Friday night and
Saturday morning. Clearing on Friday and Saturday will likely be
on the slow side for coastal areas. For Saturday night and Sunday,
will anticipate less marine layer stratus with developing
northerly flow. Temperatures will continue to exhibit a cooling
trend through Saturday, but should begin to rebound a little on
Sunday.

As for winds, gusty southwest winds will prevail through Saturday
with the strongest winds across interior sections. Do not
anticipate any advisory concerns, but it will be gusty. For
Saturday night and Sunday, northerly winds will increase in the
usual areas (Santa Ynez Range and I-5 Corridor) and low end
advisory level winds will be possible (especially near the Santa
Ynez Range).

.LONG TERM (MON-THU)...04/153 PM.

For the extended, 12Z models continue to be on the same general
synoptic page. At upper levels, ridge will build over the desert
Southwest Monday-Wednesday then will weaken on Thursday. Near the
surface, north to northeast flow will develop on Monday and
continue through Wednesday with weak onshore flow returning on
Thursday.

Main forecast issues for the extended will be winds and
temperatures. As for winds, gusty north winds will continue to
impact the area Sunday night/Monday morning with advisory level
winds likely in the north wind-prone areas. By Monday afternoon,
the flow will shift more northeasterly with sub-advisory northeast
winds expected through Wednesday. As for temperatures, expect a
noticeable warming trend Monday through Wednesday. Models indicate
LAX-DAG gradients bottoming out around -2 mb to -4 mb Monday and
Tuesday morning with weaker offshore gradients on Wednesday. At
this time, Tuesday and Wednesday look to be the warmest days with
coastal valleys climbing into the 90s.

On Thursday, weak onshore flow will return to the area as the
upper level ridges weakens. So, will expect some cooling to begin
across the area.

&&

.AVIATION...04/1813Z.

At 1718Z at KLAX, the marine layer was around 1900 feet deep. The
top of the inversion was around 3000 feet with a temp of 21C.

Overall, moderate confidence in TAFs except high confidence in
KPMD and KWJF. Low clouds continue to hug along the Santa Barbara
south coast and southern LA County coast. Clearing of cigs may
occur 20Z-22Z at KSBA and KLGB and there is a 30% chance of no
clearing. For other coastal sites south of Point Conception, there
is a 40% chance of IFR/MVFR cigs pushing back in briefly this
afternoon. The marine layer will deepen tonight with high
confidence in low clouds pushing into the coasts and valleys, but
low confidence in timing. Conditions will likely be MVFR, but IFR
conditions are possible north of Point Conception.

KLAX...Moderate confidence in TAF. There is a 40% chance that
MVFR cigs could push back over the terminal through 21Z or 22Z.
There is a 20% chance that cigs will not arrive until as late as
06Z this evening. East winds will likely remain under 10 kt
through the early afternoon, but there is a 20% chance that east
winds may be 12 kt or higher.

KBUR...Good confidence in TAF. There is a 30% chance that cigs
will arrive as early as 06Z this evening.

&&

.MARINE...04/149 PM.

Unusually strong southeast winds continue to impact much of the
waters south of Point Conception this afternoon, and will likely
continue through tonight. The strongest of these winds will
likely be focused around Point Conception and through the Santa
Barbara Channel, and some local winds to 20 kt are possible
through the gaps and channels between the islands.

Winds and seas will likely remain below Small Craft Advisory
(SCA) level through Friday. Widespread northwest winds will filter
in across the waters on Friday evening, then high confidence in
SCA level conditions developing by Saturday afternoon from the
Central Coast to San Nicolas Island. Winds will really ramp up
Saturday night with high confidence in gale force winds,
especially near and south of the Channel Islands. These winds
will generate widespread and large short period seas. A Gale Watch
has been issued and will be in effect from Saturday evening
through Sunday night, and there is moderate confidence that gales
may extend through Monday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Gale Watch in effect from Saturday evening through late
      Sunday night for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

Gusty northwest winds are possible across southern Santa Barbara
County and through Interstate 5 Corridor and Antelope Valley
Saturday night through Monday morning. A heat wave is forecast
to develop early next week.

&&

$$

PUBLIC...Thompson
AVIATION...Stewart
MARINE...Stewart
SYNOPSIS...Kaplan/Phillips

weather.gov/losangeles


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