Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 261816
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1116 AM PDT Thu Apr 26 2018

.SYNOPSIS...26/704 AM.

A trough of low pressure will gradually move across the West
Coast today through Saturday, bringing cooler temperatures and
partly cloudy skies to the area. Additionally, there will be the
potential for gusty west to northwest winds Friday through Monday.
On Tuesday, low pressure will move over the area, resulting in
the potential for some light precipitation for the area.

&&

.SHORT TERM (TDY-SAT)...26/908 AM.

***UPDATE***

As the previous discussion mentioned, the short-term forecast is
about winds and coastal stratus. Have added a wind advisory for
the Antelope Valley for this afternoon mostly for gusty conditions
near Lake Palmdale. Also adjusted the clouds to leave some along
the coast for this afternoon as am doubting total clearing. In
keeping with the general cooling story under falling heights the
temps are down a few degrees in most places this morning.


***From Previous Discussion***

Overall, 00Z models in good synoptic agreement through the period.
At upper levels, low currently off the Central CA coast will move
towards the CA coast today then across northern CA Friday and
Saturday. Near the surface, moderate onshore flow will prevail
with an increase in northwesterly flow Friday/Saturday.

Forecast-wise, main concern in the short term will be the winds.
With good onshore gradients today, there will be some gusty
southwest to west winds across the mountains and deserts. However
at this time, any advisory-level winds look to be localized, so
will not issue any advisories at this time. Beginning tonight, the
northerly offshore gradients will begin to increase with east-west
gradients remaining onshore. So for Friday and Saturday, there is
a decent chance of widespread advisory-level west winds across
the Antelope Valley. Additionally with the increasing northerly
offshore gradients (SBA-SMX peaking around -4.4 mb), advisory
level northwest to north winds look likely Friday and Saturday
for southern Santa Barbara county.

Otherwise, secondary concern will be marine layer stratus.
Currently, AMDAR soundings indicate marine inversion based around
1400 feet. With good onshore gradients, stratus should push into
the coastal valleys and Salinas Valley this morning. With upper
low moving inland Friday/Saturday, lowering H5 heights should
allow for the marine inversion to deepen. So, stratus should be
able to push further inland across Ventura/LA counties Friday
morning and Saturday morning. For southern Santa Barbara county,
increasing northerly flow should keep area stratus-free Friday and
Saturday. For the Central Coast, stratus should continue tonight
and Friday morning, but will likely be stratus-free Saturday
morning due to northwesterly flow. Additionally, increasing
northerly flow could generate some clouds across the northern
mountain slopes and interior Santa Barbara and San Luis Obispo
counties Friday night and Saturday morning.

As for temperatures, expect only minor day-to-day changes for the
area with afternoon highs a couple degrees below seasonal normals.

.LONG TERM (SUN-WED)...26/148 AM.

Overall, 00Z models in decent agreement through the extended
period. At upper levels, cyclonic flow remains over the area
Sunday/Monday with a trough/low moving over the area on Tuesday
then into AZ on Wednesday. Near the surface, decent west to
northwest flow will prevail through Monday then weaken on Tuesday
and Wednesday.

Forecast-wise, Sunday and Monday do not look too dissimilar from
Saturday. Main concern will continue to be the potential for
advisory-level Sundowner winds across southern Santa Barbara
county. There may be some clouds across LA county coast during the
night/morning hours Sunday and Monday as well as across interior
sections Saturday night/Sunday morning. Otherwise, skies should
remain mostly clear with temperatures a couple degrees below
seasonal normals.

On Tuesday, things become more unsettled as trough/upper low moves
across the area. At this time, the GFS has a track a bit closer to
the water than the ECMWF. However both models do spit out some
precipitation across the area on Tuesday. So, will go with slight
chance of showers for all areas on Tuesday. With more westerly
track, the GFS indicates a bit more precipitation than the ECMWF,
but neither models indicates the potential for any significant
precipitation event.

On Wednesday, the upper low/trough should be eastward enough to
keep any precipitation well east of the area and allow
temperatures to rebound a bit.

&&

.AVIATION...26/1811Z.

At 1730Z at KLAX, the marine layer was 2000 feet deep. The top of
the inversion was near 4300 feet with a temperature of 17C.

Persistent pattern is expected over the next 24 hours. N of Point
Conception, IFR/MVFR stratus has scoured out across KPRB and much
of the Central Coast. There is a 50% chance that cigs will linger
near KSMX this afternoon. Good confidence for similar timing
IFR/MVFR cigs once again this eve. Less confidence for KPRB which
could be delayed an hour or so from 18Z Taf.

S of Point Conception...Should be a similar timing pattern of
IFR/MVFR stratus developing this eve and scouring out Fri morning
or within an hour of today. There is a 20-30% chance that MVFR
cigs will linger through entire day at coastal airports S of Point
Conception tomorrow.

KLAX...Moderate confidence in the 18Z TAF. There is a 20-30%
chance that cigs could linger from tonight through the afternoon
tomorrow.

KBUR...High confidence in the 18Z TAF through 08z then slightly
lower confidence with timing of IFR/MVFR stratus developing
between 09-10z.

&&

.MARINE...26/1115 AM.

High confidence that winds will increase to SCA (Small Craft
Advisory) levels across the outer waters this afternoon. Winds
will likely continue at or above SCA levels across the outer
waters thru Mon. There is a 50% chance that winds will increase to
Gale Force across the southern two thirds of the outer waters
zones (PZZ673 and PZZ676) as early as Fri afternoon, with winds
possibly continuing at Gale Force levels at times thru Sun night.

Across the inner waters north of Pt Conception, there is a 20%
chance of SCA level winds this afternoon and evening. There is a
40-50% chance of SCA level winds Fri afternoon and evening, then
SCA level winds are likely Sat afternoon through Mon.

For the inner waters south of Pt Conception...there is a 20%
chance of SCA level winds across western portions of the SBA
Channel this afternoon/evening. SCA winds are likely, especially
across western portions of the zones during the afternoon and
evening hours Fri thru Mon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect from 3 PM this afternoon to 10 PM PDT
      this evening for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      PM PDT Monday for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 3
      PM PDT Friday for zones 673-676. (See LAXMWWLOX).
     Gale Watch in effect from Friday afternoon through late
      Sunday night for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

There will be potential gale force winds mainly for the outer
coastal waters during the outlook period.

&&

$$

PUBLIC...Thompson
AVIATION...Kaplan
MARINE...DB/CK
SYNOPSIS...JLL

weather.gov/losangeles



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