Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 241217

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
417 AM PST Sat Feb 24 2018

.SYNOPSIS...24/344 AM.

It will be dry this weekend with a warming trend, with daytime
temperatures near normal levels by Sunday. It will be breezy to
windy at times through early Sunday. An upper low will bring a
good chance of rain showers and mountain snow showers to the
region late Monday through Tuesday morning. Another upper system
may bring somewhat more significant rain and mountain snow to the
region Thursday afternoon through Friday.


.SHORT TERM (TDY-MON)...24/417 AM.

Clear skies across the entire forecast areas this morning. It was
rather cold, especially where winds have dropped off since clear
skies and low dew points were providing excellent radiational
cooling conditions. Frost advisories and freeze warnings were in
effect for coastal and valley areas, except a hard freeze warning
was in effect for the Santa Ynez Valley and for the Los Angeles
County coast, where only isolated frost is just a remote
possibility in the coldest locations away from coast. Under
brilliant late February sunshine, temps should rise quickly this
morning, and although it should be noticeably warmer than
yesterday, max temps will still be a few degrees below normal
in most areas.

A short wave trough will drop from the Pac NW into the Great Basin
this afternoon. This will bring a reinforcing shot of strong
northwest winds aloft to the region. At the same time, an area of
subsidence will sweep across the region. Expect NW winds to
increase to advisory levels across the Central Coast this
afternoon, and across the mtns of L.A. and VTU Counties, mainly
near the Interstate 5 corridor. Gusty west to northwest winds will
likely also reach advisory levels in the Antelope Valley. Wind
advisories have been issued for these areas.

Elsewhere, northwest winds could get close to advisory levels
across the Santa Ynez range and adjacent south coast of SBA
County this afternoon and evening. West winds could get close to
advisory levels across coastal sections of VTU and L.A. Counties,
mainly near the beaches. Winds will diminish in most coastal areas
this evening, but should stay up through late tonight in the
Antelope Valley. Gusty north winds will likely push into the
valleys of eastern VTU County and the western and northern valleys
of L.A. County as the low level flow turns more northerly tonight.

The airmass across the region will be slightly less cold tonight,
and there should be a bit more in the way of wind. Expect frost
and freeze conditions to be much less widespread, although
frost advisories may be needed on the Central Coast and in the
Ojai Valley. Low level flow will turn more northeasterly Sunday
morning, and winds will diminish. Heights and thicknesses will
rise across the region on Sunday. Max temps should rise several
more degrees, possibly reaching normal levels in most areas.

The models are in fairly good agreement with the next system that
will likely affect the region, showing a trough digging through
the Pacific Northwest Sunday night, with the trough axis sliding
southward along or just off over or just to the west of San Luis
Obispo County Monday evening. Clouds will increase Monday, and
there is a good chance of showers across SLO and SBA Counties in
the afternoon, with showers becoming likely across northwestern
SLO County late in the day. Max temps will be down several degrees
in most areas Monday.

There will be a good chance of showers across the entire forecast
area Monday night. The EC continues to be stronger, colder
and farther west with this system, gaining a bit more moisture
due to some mid level onshore flow off the Pacific. The WRF is
almost exactly a compromise between the EC and GFS with the
position and track of the upper low, but more similar in strength
to the EC. Snow levels should be rather low, generally between
3500 and 4500 feet for much of its duration, possibly down to 3000
feet. It does not look like a huge precip producer for the region,
but with such cold air aloft and marginal instability so close to
the forecast area, there is the threat of some heavier showers
Monday night. In general, would expect two to four tenths of an
inch or rain in most areas, with the highest totals likely across
SLO and SBA Counties and across eastern L.A. County. Locally
higher totals are possible if heavier showers develop.

.LONG TERM (TUE-FRI)...23/134 PM.

Cool and breezy again Tuesday behind the Monday trough but dry
through at least Wednesday and likely Thursday as well. Might have
another round of frost/freeze hazards for Tuesday morning in wind
protected areas. The last few model runs of the GFS and now the
latest ECMWF have trended much weaker with the weather system for
the end of next week. Both now push the low east into Montana
rather than drop it south off the California coast as they once
did. So while there`s still a chance of rain the amounts are a
small fraction of what they were at one time. In fact some of the
ensemble members don`t have any rain over the area, though most
support at least some light rain on Friday and a few are still
even holding out for the bigger rain producer that earlier
operational runs supported. Since our Friday pops were already
pretty conservative those have been left alone and we`ll see how
this evolves over the next few days. Given the pattern this season
it`s hard not to favor the drier scenario now offered by a
majority of the solutions.



At 1100Z, there was no marine inversion at KLAX.

Overall, high confidence in 12Z TAF package as all sites are
expected to remain at VFR levels. There will be some localized
offshore winds this morning which could result in some light
LLWS/turbulence across the valleys and mountains.

KLAX...high confidence in 12Z TAF. Any east winds this morning
will remain below 7 knots.

KBUR...high confidence in 12Z TAF. There is a 20% of light
LLWS/turbulence 12Z-22Z.


.MARINE...24/259 AM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level northwesterly winds will continue today
through Wednesday. There is a 30% chance of Gale force gusts this
afternoon/evening and again Monday afternoon/night.

For the Inner Waters, high confidence in current forecast. For the
waters north of Point Sal, SCA level northwest winds are expected
each afternoon/evening from today through Wednesday. For the
waters south of Point Conception, there is a 70% chance of SCA
level winds this afternoon/evening. From Monday night through
Wednesday, there is a 60% chance of SCA level winds, especially
across western sections.


CA...Freeze Warning in effect until 9 AM PST this morning for
      zones 34-35-44-46. (See LAXNPWLOX).
     Wind Advisory in effect from 1 PM this afternoon to 9 PM PST
      this evening for zones 34-35. (See LAXNPWLOX).
     Hard Freeze Warning in effect until 9 AM PST this morning for
      zone 36. (See LAXNPWLOX).
     Frost Advisory in effect until 9 AM PST this morning for
      zones 39-40-45-88-547. (See LAXNPWLOX).
     Wind Advisory in effect from 1 PM this afternoon to 10 AM PST
      Sunday for zones 53-54. (See LAXNPWLOX).
     Wind Advisory in effect from 1 PM this afternoon to 3 AM PST
      Sunday for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect from 2 PM this afternoon to 9
      PM PST this evening for zones 645-650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect from 2 PM this afternoon to 3
      AM PST Sunday for zones 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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