Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 231650

945 AM PDT Sat Sep 23 2017

Updated Aviation Discussion

A high along with offshore winds, breezy at times, should bring a
significant warming trend and mostly clear skies into Friday.



Upper level trough digging into Great Basin today, with northwest
flow aloft across Southwest California. Near the surface, weak
offshore flow beginning to develop this morning as evident by
some surface observations across the mountains and foothills.
As a result, satellite imagery showing mostly clear skies
across the district as of 9 am. Warming and drying trend underway
today, which will continue the next few days as offshore pressure
gradients gradually ramp upwards. For today, highs will mostly
be in the 70s in most location, with some readings into the
lower to mid 80s across the valleys. The combination of locally
gusty offshore winds, warming temperatures, lowering humidities,
and dry fuels will bring elevated fire danger to portions of
Southwest California tomorrow through much of next week.

*** From previous discussion ***

Forecast-wise, main concerns in the short term will be offshore
winds and temperatures. With respect to winds, the gradual
increase in offshore gradients will result in an increase in north
to northeast winds across the area. At this time, the upper level
support is not overly impressive, so do not anticipate any
widespread advisory-level winds through Monday. However, there
will be some locally gusty offshore winds in the usual spots
(across southern SBA county early this morning then shifting to
Ventura and Los Angeles counties today and continuing through

Otherwise, the overall synoptic pattern (increasing offshore
surface gradients and increasing thicknesses/H5 heights) will
result in a warming trend across the area through Monday. In fact
by Monday, most coastal and valley areas will be a few degrees
above seasonal normals. Additionally, overnight lows will be
gradually increasing through the period.

As for clouds, generally mostly clear skies will prevail through
the period. There will be some patchy stratus/fog this morning
along the Central Coast, but otherwise coastal and valley areas
are expected to remain stratus-free through the period.


Overall, 00Z models exhibit decent synoptic agreement through the
period. At upper levels, low develops over the eastern deserts on
Tuesday and meanders across the eastern deserts and Great Basin
through the period. Near the surface, offshore flow will continue
although the flow should weaken by the end of next week.

Forecast-wise, main concerns will continue to be offshore winds
and temperatures. Northeasterly winds will continue through the
period with the strongest winds likely Tuesday/Wednesday.
Depending on exactly where the upper low meanders, the upper level
support could increase or decrease. At this time, still do not
anticipate any widespread advisory-level winds across the area,
but this possibility will need to be closely monitored the next
few days. As the offshore winds continues, skies should remain
mostly clear for all areas as stratus development should be nil.

With the continued offshore flow, temperatures will remain well
above seasonal normals through the period with next Friday
potentially the warmest day. Overnight lows will also remain warm
through the period.



At 17Z at KLAX...There was no marine layer or inversion.

High confidence in VFR conditions almost everywhere through
Sunday. Only exceptions being a 20 percent chance of LIFR FG at
KSMX 10Z-16Z Sunday, and a 10 percent chance of BKN015 conditions
at KLGB KLAX 09-16Z Sunday. Onshore winds today will be similar
but slightly weaker than yesterday. Extended period of offshore
winds for valleys and mountains will begin on Sunday.

KLAX...10 percent chance of BKN015 09-16Z Sunday, otherwise high
confidence in VFR. East winds likely Sunday morning, but only a 10
percent chance of exceeding 8 KT.

KBUR...High confidence in VFR through Sunday. Breezy offshore
winds will form over the region starting Sunday, but will not
surface at the airport.


.MARINE...23/900 AM.

Confident in low-end Small Craft Advisory (SCA) level winds
continuing over the outer waters through tonight, especially
between Point Conception and San Nicolas Island. The western Santa
Barbara Channel will also see low-end SCA winds this evening, but
should be localized and brief enough to not need an Advisory. All
areas will experience a short-period chop from these winds into
Sunday. No expecting SCA winds through the middle of next week,
but afternoon and evening onshore winds will get into the 10 to 20
KT range everywhere starting Sunday with the warm conditions
inland. Pockets of dense fog at times cannot be ruled...please
stay aware of your immediate environment.


PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).


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



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