Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 191638

938 AM PDT Tue Sep 19 2017

A low will hang over the area this week with low clouds and fog for
the coast and some valleys. Cold Canadian air will move in by
Wednesday for breezy winds from Santa Barbara and northward. There
may be a possibility of preciitation for Los Angeles county on
Thursday with major temperature drops inland. Next week, offshore
flow should bring a warming trend into midweek.



Marine layer up to around 4000` south of Pt Conception this
morning with some patchy drizzle around. Highs will again be
several degrees below normal inland and slightly below normal at
the coast. Clouds will be slow to clear and some areas may stay
cloudy well into the afternoon.

Up north the northwest flow and cool air at lower levels has
weakened the inversion and dissipated most of the low clouds.
Gusty northwest winds expected today along the Central Coast will
keep temps near to slightly below normal in most areas. Further
inland the morning started with some low clouds pushing in from
the San Joaquin Valley but those should dissipate by late morning
with highs 4-8 degrees below normal.

***From previous discussion***

The Axis of the upper low pinwheels to the south and east
Wednesday night and Thursday and drags a weak and dry cold front
through the area. The lift from the trof along with eddy will keep
low clouds across the coasts and vlys of VTA and LA counties. By
morning the slight energy imparted by the front should be enough
to bring a slight chc of showers across srn LA county...esp the
San Gabriel Vly. The clouds should dissipate during the afternoon
except for th SAN Gabriel Vly where clouds and a slight chc of
showers will persist. Hgts will fall to 565 DM which is about 20
DM below normal. Thursday will be the coolest day of the next 7
with vly temps 10 to 15 degrees below normal. (only 2 to 5 degrees
blo normal for the coasts)

The West Coast trough deepens quite a bit Wednesday night into
Thursday. With the cooler air aloft the marine layer should deepen
quite a bit Thursday morning and it looks like a good
drizzle/light rain scenario for areas south of Pt Conception,
especially up against the south facing slopes. Probably another
reverse clearing day as well and highs a good 10-15 degrees below
normal for inland areas.


Not much change Friday. The cold air will have wiped out most of
the marine clouds everywhere except for southern LA county. Hgts
will rise slightly and the strong onshore flow will relax a little
so look for 1 to 2 degree of warming.

On Saturday there will still be some morning low clouds across
southern LA county but there will be Sunny skies everywhere else.
Hgts will continue to rise and there will be offshore trends.
Almost all areas will see 2 to 4 degrees of warming. Max temps
will still be below normal but only by a few degrees.

Weak offshore flow will set up Sunday and Monday (and likely a few
days past that) it will keep the skies clear and will kick off a
decent warming trend. There does not look like there is enough
upper or thermal support for a Santa Ana event just enough to warm
things up and dry things out. Max temps will climb each day and
the csts and vlys will see above normal temps with plenty of upper
80s and lower 90s in the vlys by Monday.



At 1131z at KLAX... the inversion was around 3000 ft. The top of
the inversion was around 3700 ft with a temperature of about 19
degrees Celsius.

Overall... Low to moderate confidence in the current coastal and
adjacent valley TAFs and high confidence in the remaining TAFs.
IFR/MVFR conditions will be hit and miss at the coastal and
adjacent valley terminals north of KOXR this morning and fairly
solid from KOXR and southward. Conditions will be VFR by 20z at
Los Angeles County terminals and by 18z elsewhere. Reduced
conditions will return to coastal and coastal adjacent valley
terminals in Los Angeles County terminals 01z-05z and to KCMA...
KOXR... and KSBA in the 05z-11z period. Otherwise and elsewhere
VFR conditions will prevail.

KLAX... Moderate confidence in the current TAF. Conditions will
clear by 20z then will return to IFR/MVFR about 01z. Otherwise
VFR conditions will prevail. No east winds greater than seven
knots are expected during the forecast period.

KBUR... Moderate confidence in the current TAF. Conditions will
clear by 19z then will return to IFR/MVFR by 05z. Otherwise VFR
conditions will prevail.


.MARINE...19/900 AM

Northwest winds over the outer waters will be at Small Craft
Advisory (SCA) levels early today then increase to Gale
Warnings... which are posted from this afternoon through late
Wednesday night. The strong winds will likely last into Thursday
but may decrease slightly to a strong SCA level.

SCA level winds will develop across the northern inner waters
this afternoon through late Wednesday night and may remain strong
through Friday. Western portions of the Santa Barbara Channel
will have SCA level winds through late tonight and possibly into
Wednesday. Winds in the inner waters will be strongest during the
late afternoon to evening hours.

Combined seas will increase through Wednesday as building short
period waves combine with the first northwest swell of the season.
Seas will grow to 6 to 8 feet at 15 seconds today and to 7 to 10
feet at 14 seconds on Wednesday.


PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Thursday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Wednesday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zones 670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM this afternoon to 3 AM PDT
      Thursday for zones 670-673-676. (See LAXMWWLOX).


Gale winds are expected across the outer waters Thursday. Wind
advisories might be needed for southern Santa Barbara County Coast
Thursday evening.



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