Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 231243

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
443 AM PST Fri Feb 23 2018

.SYNOPSIS...23/342 AM.

An upper trough will exit the region this morning. Scattered snow
showers in the mountains will end. Otherwise, it will be cool and
breezy today. Tonight will be cold across the region with frost or
freezing temperatures possible away from the coast. Dry and
somewhat warmer weather is expected over the weekend. A couple of
storm system may bring some rain to the region next week, most
likely late Monday into Tuesday, and again by Thursday.


.SHORT TERM (TDY-SUN)...23/403 AM.

Satellite imagery showed clouds piling up again the northern mountain
slopes in the moist northwest flow aloft. Radar was showing some
echoes across northern VTU County and northwestern L.A. County,
and there have been reports of moderate snow sticking to portions
of Interstate 5 near the junction of Highway 138. Snow levels were
between 2500 and 3000 feet. Although snow showers were mostly
confined to the mountains, would not be surprised if there are a
few snow showers in the Antelope and Cuyama Valleys early this
morning, especially in the foothills.

Snow showers should end across the region by late morning. Expect
local storm total snow accumulation of 1 to 3 inches in the mtns
of VTU County and northwestern L.A. County, and possible across
the eastern San Gabriels. A local dusting to an inch of snow is
possible in the foothills above the Cuyama and Antelope Valleys.

Gusty northwest winds were also affecting the mountains this
morning. Once the Winter Weather Advisory expires later this
morning, wind advisories will probably be needed there through at
least this evening. Elsewhere, skies were mostly clear, except
partly cloudy in the San Gabriel Valley. An isolated shower is
possible there through mid morning, but otherwise it should be dry
today. Gusty northwest winds will likely reach advisory levels on
the Central Coast today, and across the mtns and adjacent south
coast of SBA County as well. Advisory level west to northwest
winds are likely in the Antelope Valley through this evening. Even
across coastal sections of L.A. and VTU Counties, winds may get
close to advisory levels, especially near the coast. It will be
very chilly across the entire forecast area today, with max temps
at least 5 to 10 degrees below normal.

It will be clear tonight. Winds should decrease to below advisory
levels in most areas this evening, although may stay gusty in the
mountains. Where the winds drop off tonight, it will become quite
cold. Freeze Watches are in effect for the Central Coast, the
Interior Valleys of Ventura County, especially for the Ojai
Valley, and the Santa Monica Mountains. A Hard Freeze Watch has
been posted for the Santa Ynez Valley. Frost advisories may have
to be considered for the south coast of SBA County, the VTU County
coast, the coastal valleys of VTU County, and possibly the San
Fernando and Santa Clarita Valley. Will let the day shift assess
that further, since there is still some question as to whether
on not there may be too much winds tonight.

Dry weather is expected over the weekend. Max temps should be up a
couple of degrees on Saturday, then several more degrees on
Sunday, with temps possibly getting close to normal levels. There
may be another bump up in the north winds late Sat into early
Sunday, mainly from southeastern SBA County through L.A. County.
Where there is no winds, it will be another cold night Sat night,
with freezing temps possible in some coastal and valley areas.

.LONG TERM (MON-THU)...23/442 AM.

A trough will dig southward from the Pacific NW on Mon. Heights
across the region will fall and onshore flow will increase. This
should bring a few degrees of cooling to the forecast areas,
especially west of the mtns. Clouds should increase in the
afternoon, mainly across northern sections. There is a slight
chance of showers north of Pt Conception late in the day, but
overall it should be a dry day.

The models have come into better agreement with this next system,
with the EC backing off its track well out over the water
gathering a fair amount of Pacific moisture, and the GFS slightly
farther west and a bit wetter. Both models show the system
digging through CA Monday afternoon, with the trough axis right
along or just off the coast, then show it closing off right across
SBA County Mon night. It then is forecast to move eastward into
the deserts on Tue. At this point, it appears as though there will
be a chance of showers across the region Mon night into Tue,
possibly lingering into Tue evening across eastern L.A. County. By
no means does this look like a large rain maker for the region,
with generally one tenth to one third of an inch of rain expected.
However, if it tracks a bit farther west and gathers some moisture,
totals could be somewhat higher. The EC is stronger and colder
with the upper low, suggesting rather low snow levels, probably
in the 3500 to 4500 feet range. Still too early for those details
yet, especially with the models changing from run to run.

Dry weather is expected late Tue night through Wed. Beyond Wed,
the models are very different. The EC shows a sharp negatively
tilted trough approaching the Pac NW Thu, a strong jet sagging
southward into the forecast area, heights dropping to 550 dm by
Thu afternoon, and rain spreading into the region. The 06Z GFS
slower, weaker and farther north with the upper trough, maintains
566-570 dm heights across the region through Thu and keeps it dry.
Have decided to make few changes to the forecast for Thu, keeping
the chance of rain in most areas. However, the trend of the GFS
is am eye-popping one, and suggests little if any rain across the
region for the end of the week.



At 1115Z, there was no marine inversion at KLAX.

Overall, high confidence in 12Z TAF package. VFR conditions are
anticipated for all sites through the TAF period. There is a 20%
chance of MVFR conditions at all sites 12Z-20Z. Gusty
northwesterly winds will prevail with LLWS/turbulence likely
through/below mountain passes.

KLAX...high confidence in 12Z TAF. There is a 10% chance of MVFR
CIGs 12Z-18Z.

KBUR...high confidence in 12Z TAF. There is a 10% chance of MVFR
CIGs 12Z-18Z.


.MARINE...23/316 AM.

For the Outer Waters, good confidence in current forecast. Gale
force winds will continue through this evening with a 70% chance
of Gale force winds continuing Saturday and Saturday night.
Therefore, the GALE WARNING may need to be extended by future
shifts. For Sunday through Tuesday, Small Craft Advisory (SCA)
level winds are likely (80% confidence).

For the Inner Waters, moderate confidence in current forecast. For
the waters north of Point Sal, there is an 80% chance of SCA level
winds each afternoon/evening today through Tuesday and a 30%
chance of Gale force gusts this afternoon/evening and again Friday
afternoon/evening. For the waters south of Point Conception, SCA
level winds will continue through this evening with a 70% chance
of SCA level winds Friday afternoon/evening. On Monday and
Tuesday, there is a 70% chance of a repeat of SCA level winds in
the afternoon/evening hours.


CA...Wind Advisory in effect from noon today to 9 PM PST this
      evening for zones 34-35. (See LAXNPWLOX).
     Freeze Watch in effect from late tonight through Saturday
      morning for zones 34-35-44-46. (See LAXNPWLOX).
     Hard Freeze Watch in effect from late tonight through
      Saturday morning for zone 36. (See LAXNPWLOX).
     Wind Advisory in effect until 10 PM PST this evening for
      zones 39-52. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 10 AM PST this
      morning for zones 53-54. (See LAXWSWLOX).
     Wind Advisory in effect until 9 PM PST this evening for zone
      59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 PM PST this evening
      for zones 645-650-655. (See LAXMWWLOX).
     Gale Warning in effect until 9 PM PST this evening for zones
      650-655-670-673-676. (See LAXMWWLOX).



Low elevation snow possible Monday night into Tuesday creating
hazardous driving conditions in the mountains, especially across
the Interstate 5 corridor.



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