Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 230617

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1117 PM PDT Thu Mar 22 2018

.SYNOPSIS...22/640 PM.

The cold front will exit the area by early Friday morning.
A trough of low pressure will keep temperatures cool with breezy
winds through Monday. A warming trend is expected Tuesday into


.SHORT TERM (THU-SUN)...22/715 PM.


Post frontal trof is over Western SBA county and extends to the NE
into the center of SLO county. This trof is moving slowly to the
east. There is quite a bit of instability with this trof and it is
producing numerous showers and will likely spawn a few TSTMs over
the next couple of hours. There is only a very small chance of a
shower in the wake of this trof. The showers with this trof will
be fairly heavy and could be heavier if any TSTMs develop. The
flash flood watch for the burn areas in LA county continues due to
the threat of the TSTMs over the area this evening.

The heavier showers will make their way through SBA county and
then into VTA county and finally into and then out of LA county a
little after midnight.

Forecast is still on track for a partly cloudy day on Friday with
continued cool max temps.

Will issue a forecast update to change rain from "likely" to
"scattered showers" and to remove the wind advisory.

***From Previous Discussion***

The deep plume of moisture that has been over our area the last
two days is finally shifting east as the upper low over the
eastern Pacific and associated cold front moves onshore.
Precipitable waters are dropping pretty fast now but still
hovering in the .75-.90" range which is still above normal. What`s
left now is the cold front passage and associated instability that
will come through late this afternoon and evening. The line of
showers stretching southwest from nrn SLO County is the leading
edge of the front and while there has not been a history of
thunderstorms with it yet models do indicate increasing
instability as it moves east and into the Channel Islands region
this evening. So the forecast will continue to have thunderstorm
chances through this evening, especially the southern part of the
forecast area. Given the pwats have dropped below an inch the
concern for significant flash flooding and debris flows has
lessened but not gone away completely. The watch covering the
western portion of the forecast area will still expire at 5 while
the LA County watch goes through 5 am Friday, though given the
speed at which the front is moving it`s likely this watch will be
able to be cancelled as early as midnight.

So in short, the threat still exists for damaging debris flows but
now that we`re in the convective part of the system any storms
that form will be very isolated and the chances of them hitting
any one area are pretty small. With the lower pwats now and storms
moving a little faster it will be more difficult, though not
impossible to reach critical rain rates for debris flows.
Additional rainfall amounts will vary from basically just trace
amounts to as much as a .50-.75" where the heavier downpours

By dawn Friday all precip should be east of the area. Temps will
remain on the cool side with some breezy northwest winds possible,
especially SLO/SB counties.

Over the weekend models continue to show a weak trough moving into
northern California with the southern edge of it brushing SLO/nrn
SB Counties. Any precip from it would be very light, less than a
tenth of an inch. Behind it Saturday night into early Sunday some
upslope snow showers are possible over the Grapevine. Farther
south just partly cloudy skies and continued cool temps.

.LONG TERM (MON-THU)...22/139 PM.

The weekend trough will evolve into a cutoff low over the Great
Basin and settle over the Colorado River on Tuesday before moving
east on Wednesday. Cool northerly flow Monday will prevent temps
from warming up too much despite some downslope warming from the
weak offshore flow. As the low moves into AZ and NM offshore
gradients will increase and possibly enough for some low end wind
advisories in Ventura/LA Counties Tuesday and Wednesday. Slight
warming expected Tuesday but better warming Wed/Thu with highs at
lower elevations in the 70s. Gradients are expected to trend
onshore Thursday afternoon so likely a little cooling at the coast
but continued warming inland. Looks like the dry pattern should
continue into next weekend.



At 0545Z at KLAX, there was no marine layer nor a sfc based

Low confidence all TAFs through 20Z then good confidence. Cigs and
Vis will vary frequently during the rain. After the rain stops
random cig layers will likely form and dissipate. LIFR conds are
possible at all sites through 16Z.

KLAX...Low confidence in TAF through 20Z. Cigs and Vis will vary
frequently. There is a 30 percent chc that east winds will end by
08Z. There is a 30 percent chc that MVFR cigs will hold off until

KBUR...Low confidence in TAF through 20Z. Cigs and Vis will vary
frequently. There is a 30 percent chc of LIFR conds through 18Z.


.MARINE...22/810 PM.

Generally good confidence in the current forecast. For the outer
waters, Small Craft Advisory (SCA) winds will affect the entire
area tonight and Fri, and until 05Z Fri evening for PZZ670, thru
10Z late Fri night for PZZ673, and thru at least 22Z Sat
afternoon for PZZ676. Winds should come up again Sat night and
Sun, with 50%-60% chance of SCA winds Sun thru Tue.

For the inner waters N of Point Conception, there is a 20% chance
of SCA winds this evening western portion, and a 30%-40% chance
of SCA winds Sat evening and Sun evening, otherwise winds and seas
should remain below SCA thru Sun night. A 40% chance of SCA wind
gusts can be expected Mon as well.

Across the inner waters S of Point Conception, winds and seas will
remain below SCA thru Fri, then there is a 50% chance of SCA
winds Fri night thru Sun and again Sun nigh thru Mon.

Isolated thunderstorms are possible at times across the southern
waters through this evening. Brief gusty and erratic winds will
be possible near any thunderstorm.


CA...Flash Flood Watch in effect until 5 AM PDT Friday for zones
      41-46-54-88-547. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 9 PM PDT Friday for zone
      670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zone 673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Saturday for
      zone 676. (See LAXMWWLOX).



No significant hazards expected.



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