Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 221149

449 AM PDT Fri Sep 22 2017

...Aviation discussion updated...


Upper level low pressure will persist over the western United States
through Saturday, keeping temperatures below normal. An upper
level ridge will move toward the West Coast Sunday, and offshore
flow will develop. This will bring significant warming, especially
to coastal and valley areas. Upper level high pressure and weak
offshore flow should keep temperatures above normal for much of
next week, with mostly clear skies through the period.



Skies were mostly clear across the region, with the exception of a
few patches of clouds here and there, mainly across southern and
eastern L.A. County and on the northern slopes. These clouds
should be gone by mid morning, although there may be enough
moisture for some stratocu development late this morning and this
afternoon. Overall, though, expect a mostly sunny day across the
region. Due to the increase in sunshine, max temps should be up a
few degrees, but will still be 4-8 degrees below normal in most
areas, except more than 10 degrees below normal in the mtns,
deserts and interior valleys. Gusty northwest winds on the Central
Coast and west winds in the Antelope Valley will likely stay below
advisory levels this afternoon and evening. There will be another
round of gusty nw-n winds through and below passes and canyons of
the Santa Ynez Mountains and adjacent south coast of SBA County
this evening, but with less in the way of upper support, winds
will probably remain just below advisory levels.

The elongated upper low across Idaho and Nevada will move only
very slowly eastward tonight and Saturday. Expect skies to be
mostly clear tonight/Sat, except for coastal sections of L.A.
County, where there may still be a marine inversion, and some low
clouds may develop late tonight and linger through mid morning
Sat. Max temps on Sat should be about the same as those reached
today, except there should be a few degrees of warming in the
interior valleys, mountains and the Antelope Valley.

The upper low will eastward Sat night and Sunday, while an
upper ridge amplifies in the eastern Pacific and moves
toward the West Coast. Low level gradients are forecast to turn
offshore Sunday morning, and could be strong enough to produce
some locally gusty northeast winds in the mtns and valleys of
L.A. and VTU Counties. Heights will rise significantly on Sunday,
so expect significant warming, especially west of the mountains
where downsloping northeast flow will add to the warming. Max
temps will likely get close to 90 degrees across the warmer
locations in the valleys on Sunday.


The upper ridge will continue to approach the West Coast Mon, and
heights/thicknesses will rise. Offshore flow will be a bit stronger
Mon, so there should be a bit more in the way of gusty northeast
winds across L.A./VTU Counties, especially in the mtns and
valleys. Max temps should be up a few degrees in most areas Mon.

The models now diverge a bit beyond Mon. The GFS shows the ridge
axis moving into the Pac NW and northern CA by late Tue, then into
the West Coast Wed and Thu, while a very weak upper low develops
west of the forecast area on Thu. Low level offshore flow would
peak on Tue, but would remain weakly offshore through Thu. This
would result in very warm to hot weather in most areas Tue through
Thu with well above normal temps. The EC shows shortwave energy
dropping southward into Great Basin Tue, with an upper low
developing in southern Nevada, then this upper low will linger
through early Thu before moving east. Low level flow is also
forecast by the EC to be weakly offshore, at least Tue and Wed.
This scenario has somewhat lower heights across the region Tue
through Thu than does the GFS, but interestingly enough, the
forecast max temps on the EC numerical guidance are close to
those of the GFS, though slightly lower. Overall, still have
fairly high confidence that temps will be well above normal Tue
through Thu, and skies will be mostly clear through the period.



At 11z at KLAX... there was no inversion in the lower atmosphere.

Overall... Moderate to high confidence in the current TAFs. There
is a fifteen percent chance of MVFR CIGs at coastal terminals in
Los Angeles and Ventura Counties through 16z. Otherwise and
elsewhere VFR conditions will prevail.

KLAX... Moderate to high confidence in the current TAF. There is
a fifteen percent chance of MVFR CIGs through 16z. Otherwise VFR
conditions will prevail. No east winds greater than seven knots
are expected.

KBUR... High confidence in the current TAF. VFR conditions will


.MARINE...22/200 AM.

Small Craft Advisory (SCA) level northwest winds will continue to
diminish across the coastal waters today. Winds will diminish to
below SCA levels across the inner waters by late morning and
across the outer waters by late afternoon. There is a thirty
percent chance that the winds across the central and/or southern
outer waters will remain above SCA levels into the evening.

Steep short-period seas will affect much of the coastal waters
today and tomorrow.


PZ...Small Craft Advisory in effect until 9 AM PDT this morning
      for zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zones 670-673-676. (See LAXMWWLOX).


It will be hot Monday through Thursday, especially away from the
coast. There will be gusty northeast winds at times, especially
across Los Angeles and Ventura Counties Monday and Tuesday. The
combination of heat, gusty winds and low relative humidity values
will bring heightened fire danger, especially to the mountains and


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