Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 171228

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
528 AM PDT Sat Mar 17 2018

.SYNOPSIS...16/509 PM.

Below normal temperatures should continue into Sunday, then
the air mass should warm to normal through Tuesday. Showers are
possible precipitation into Saturday evening, then a drying trend
is expected Sunday through Tuesday. A significant storm system
could bring widespread rainfall to the region between Tuesday and


.SHORT TERM (TDY-MON)...17/319 AM.

A 538 DM upper low was over south central Oregon. A trof has just
exited the area and there are only a few showers left over the
forecast area. Skies will generally be partly cloudy this morning.
There will be a little more cloudiness across the mtns as well as
the Central Coast where some stratus has developed. The upper low
will push into Idaho this afternoon and a fairly sharp trof will
move into SLO county. There is a fair amount of cold air aloft
with this trof as well so in addition to the lift there will be
enhanced instability. This trof will bring showers first to SLO
county and then will move through SBA VTA counties later in the
afternoon and early evening before moving through LA county late
this evening. There will be a 2 to 3 hour period of shower
activity with the trof passage. The best instability will be along
the Central Coast and esp near the Kern county line. Enough
instability to create a slight chc of TSTMs later this afternoon
and evening. The best rainfall rates will be near the Kern county
line with lesser non threatening rainfall rates over the coasts
and vlys where the burn scars are. Most areas will see about a
a tenth or two tenths of an inch of rainfall today with some half
inch amounts under areas the see the heavier showers. Snow levels
will fall to 4000 feet this afternoon and then 3500 feet this
evening. A winter weather advisory is in effect for the
SBA/VTA/LA mtns where 3 to 6 inches of snow is possible through
early Sunday morning. 552 DM hgts will keep max temps in the upper
50s and lower 60s for most of the coasts and vlys.

Flat flow with plenty of high level clouds is on tap for Sunday.
It will be dry but not very warm. Hgts only rise to 562 DM and max
temps across the coasts and vlys will only reach into the lower
60s or about 10 degrees blo normal.

Better ridging on tap for Monday and hgts will climb up to 576 DM.
Which is actually a little above normal for this time of year.
There will be a little offshore push from the north and only very
weak onshore flow to the east. Max temps will bump up 4 to 8
degrees and will be only a degree or two blo normal.

.LONG TERM (TUE-FRI)...17/406 AM.

All eyes remain on the extend period. Both the GFS and the EC have
begun to exhibit some run to run consistansy as well as agreeing
with each other on the broad synoptic features. There is still
considerable disagreement and inconsistancy with both mdls on the
finer details.

This event will be more of a small atmospheric river event
originating from the SW. So it will not look like a classic gulf
of Alaska cold front rain event. Right off the bat this means that
this system will be much warmer the last few. The rain will
actually start to develop over the Central Coast while the state
is under a ridge. At one time Tuesday was going to be the warmest
day but now it looks like there will be a thick cloud shield and
rain developing over SLO and western SBA counties.

Very moist SW flow then continues over the area from Tuesday night
to Thursday evening before a trof sweeps over the state and ushers
in drier NW flow.

There will likely be periods of Rain across Southern CA Wed and
Thu and depending on how the moisture transport sets up there
could be some very significent amounts of rain esp across the
coastal foothills and slopes. In fact...if the current GFS is
correct (The EC does not agree) this will be the most powerful
storm of the season. In 24 hours time the begining of this storm
will be captured by the WRF mdl run and this will hopefully allow
for an increasingly detailed forecast.

If the storm does not slow down Friday will be a drying out day
with diminishing clouds.



At 1215Z AT KLAX, there was no marine layer nor a sfc based

Moderate confidence in 12z TAFs. There is a 30 percent chc of IFR
and 20 percent chc of LIFR conds at all TAFs KSBA southward
through 18Z. There is a 20 percent chc that KSMX and KSBP will
stay VFR.

KLAX...Moderate confidence in 12Z TAF. There is a 40 percent chc
of IFR and 20 percent chc of LIFR conds through 18Z. Better
confidence in TAF after 20Z. Very high confidence that there will
be no east winds.

KBUR...Moderate confidence in TAF. There is a 30 percent chc of
IFR and 20 percent chc of LIFR conds through 16z. Better
confidence in TAF after 18Z.


.MARINE...17/519 AM.

Outer Waters...Have issued a SCA for the southern zone PZZ676 from
this afternoon through late tonight. NW winds with gusts between
25 to 30 kt. The southern portion of zone PZZ673 will experience
local gusts to 25 kt. Winds N of Point Sal will remain below SCA
thresholds. There is a 40% chance that PZZ673 will need a SCA for
the same time period as the zone to the south. The northern zone
will remain below SCA levels. Moderate confidence that the outer
waters will remain below SCA thresholds after late tonight or
early Sunday morning.

Inner Waters S of Point Conception...Have added SCA for both the
inner waters zones as they will both experience wind gusts between
25 and 30 kt late this afternoon through the overnight hours.

Another disturbance will cross the area today with scattered
showers across portions of the waters. Have taken down the slight
chance for thunderstorstorms over the northern waters.


CA...Winter Weather Advisory in effect until 5 AM PDT Sunday for
      zones 52>54. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Sunday for zones 650-655-676. (See LAXMWWLOX).



Periods of moderate to heavy rain are possible Wednesday or
Thursday of next week. Rainfall rates during this time may exceed
USGS thresholds for debris flows for recent burn areas.



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