Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 291757
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1057 AM PDT Wed Mar 29 2017

.SYNOPSIS...
Weak high pressure aloft and offshore flow will support well above
normal temperatures today. A trough of low pressure will bring
cooler conditions for Thursday and Friday with another round of
gusty northerly winds. A brief warmup is likely this weekend with
high pressure aloft nosing into the region, before another trough
brings cooler and breezy conditions early next week.

&&

.SHORT TERM...(TDY-FRI)

Winds are underwhelming this morning as upper support is weak and
even gradients are about half what the models had shown for today.
So the advisories have been cancelled and now we`ll wait for the
next burst of northerly winds late Thu into Fri. Based on the 12z
models today this next event looks just as strong as the previous
north wind event Monday night into early Tuesday so we`ll likely
be issuing high wind watches for the mountains, including the
Santa Monicas, and Antelope Valley. Strong advisories will be
needed in many other areas.

In the meantime, a warm day today with some lower 90s possible in
the warmer valleys and 80s for inland parts of the coastal zones.
Will probably fall short of the records but only by a few degrees.

***From previous discussion***

The ridge axis will move east of the region later today, then an
upper level trough will move into the Pac NW tonight and early
Thu. It will then close off into an upper low as it moves into the
Great Basin Thu afternoon. The WRF shows an eddy circulation
across the inner waters tonight, and it is possible that some low
clouds/fog could push into coastal sections of L.A. County late
tonight and Thu morning, but at this point, that seems like a low
probability. Similarly, some low clouds could also develop on the
Central Coast.

A dry frontal system will move through northern sections of the
forecast area Thu. Strengthening winds aloft and a good area of
subsidence will overspread the region during the day. Gusty west
to northwest winds should develop in the mountains, in the
Antelope Valley and on the Central Coast during the afternoon, and
winds will likely reach advisory levels in these areas. Max temps
should be down 8 to 12 degrees in most areas on Thu.

The upper low will drift east southeastward Thu night, reaching
the Four Corners area Fri morning. Strong northwest winds at 700
and 850 mb, and decent subsidence will likely bring widespread
advisory level northwest to north winds Thu night, transitioning
to a more nely direction Fri morning. This wind event looks quite
similar to that which occurred Mon night and Tue morning, though
perhaps a bit less strong. The winds will drop off across the
Central Coast Thu evening, but elsewhere, expect advisory levels
winds across the mtns and south coast of SBA County, the mtns of
L.A. and VTU Counties, the Santa Clarita Valley, much of the San
Fernando Valley and the valleys of VTU County, the Los Angeles
County coast below passes and canyons from Malibu to the Hollywood
Hills and the Westside of Los Angeles. There may be some High
Wind Warning level gusts in the mtns, but it looks as though those
will be localized.

There will likely be some low clouds on northern and interior
slopes as northerly upslope flow pushes into those areas, but
do not expect any precipitation. Winds will diminish in most
areas Fri afternoon. Max temps on Fri should be similar to those
on Thu, or perhaps down a couple of degrees in some areas.

.LONG TERM...(SAT-TUE)

An upper ridge will build into the region Sat, causing heights and
thicknesses to rise. Offshore low level flow will continue, with
some gusty winds, but below advisory levels. Expect significant
warming across the region Sat, with temps back into at least the
lower 80s in the valleys. A trough will approach with West Coast
Sunday, and low level flow will turn onshore. Expect a few degrees
of cooling, especially across the coastal plain.

The trough will move through the West Coast north of the forecast
area, then into the Great Basin Monday, likely bringing a bit
more cooling to the region. However, the GFS now shows a weaker
system than it showed on last night`s run, so cooling will be less
dramatic, and there is no longer a chance of rain. The trough will
move into the Rockies and southern plains states on Tue. A broad
wnw flow pattern will set up across the region, with heights rising
slightly, and only minor changes in max temps expected.

&&

.AVIATION...29/1800Z

At 1800Z, there was no marine layer at KLAX.

High confidence in the current forecast through 09Z. Very low
confidence for the Los Angeles coastal TAFs after 09z. The big
question is whether IFR ceilings will make into KLAX and KLGB late
tonight and with no sign of any clouds in the coastal waters, we
decided to hold off for now.

Even though Thursday evening is just outside of the forecast
period, there is a significant chance of a brief period of
northerly cross winds at KLAX for Thursday evening into very early
Friday morning. The most likely period for this activity will be
04Z to 09z.

KLAX...High confidence in the current forecast through 09Z. There
is a 50 percent chc of IFR cig/vis after 09Z.

KBUR...High confidence in the current VFR forecast.

&&

.MARINE...29/900 AM

Across the Outer Waters...A combination of winds and seas will
keep Small Craft Advisory conditions through at least Thursday
morning. Gale force winds are likely Thursday afternoon through
Friday.

Across the Inner Waters... Strong SCA winds will affect the
western portions of the inner waters on Thursday and Friday with a
40 percent chc of gale force winds.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 2 PM PDT this afternoon
      for zones 34-35. (See LAXCFWLOX).
     Beach Hazards Statement in effect until 3 PM PDT this
      afternoon for zones 40-41-87. (See LAXCFWLOX).
     High Wind Watch in effect from Thursday evening through
      Friday morning for zone 46. (See LAXNPWLOX).
     High Wind Watch in effect from Thursday afternoon through
      Friday morning for zones 52>54. (See LAXNPWLOX).
     High Wind Watch in effect from Thursday afternoon through
      late Thursday night for zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 PM PDT Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 1 PM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).
     Gale Watch in effect from Thursday afternoon through Friday
      afternoon for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(FRI-TUE)
Gusty north winds will affect portions of the region Friday
morning.

&&

$$

PUBLIC...MW/DB
AVIATION...Sweet
MARINE...Sweet
SYNOPSIS...Munroe

weather.gov/losangeles



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