Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 202033

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
133 PM PDT Tue Mar 20 2018

.SYNOPSIS...20/1023 AM.

The temperatures will be below normal into Friday. A significant
precipitation storm is forecast to arrive by Tuesday and persist
into early Friday. The storm should make an exit on Friday. Then
skies will clear, with a warming trend for the weekend and into


.SHORT TERM (TDY-FRI)...20/131 PM.

Big plume of subtropical moisture still on track to bring rain to
the area through Thursday night. The question remains where and
when will the heaviest precip occur and will there be convection
with it. Currently radars show some light precip just off the
coast that will move in later this afternoon and evening. However,
later tonight the moisture plume will shift south and will
interact with the topography as winds shift to the south/southwest
to increase rain rates. Both the 12z NAM and GFS show the first
strong burst of rain coming early Wednesday with the focus on srn
SB County and western Ventura County. This also jives well with
some higher res models. Still don`t have a lot confidence in the
precise location and rates mainly because models have been
bouncing around a lot from run to run, but they might be keying
on some increase in instability to assist with the rainfall
intensity. Didn`t see enough in the forecast soundings to justify
thunderstorms near the mainland tomorrow morning but it`s not a
zero chance either. If the conditions pan out as models are
showing rainfall rates will peak in the .50-.75"/hr range and with
thunderstorms that could go as high as an inch per hour.

Across LA County precip expected to remain fairly light and
perhaps in some far eastern areas not even measurable through

Models showing the next burst of precip coming late Wednesday
night into Thursday as the moisture starts to interact with a cold
front coming through. This might provide the best environment for
thunderstorms, though again stability parameters are pretty
marginal. CAPE values remain low, though LI`s do go briefly
negative with the frontal passage Thursday morning. This is also
when LA County will likely see their heaviest rain as the
moisture plume shifts south. Rainfall rates should be similar to
what occurs late tonight and early Tuesday.

Rain will taper off Thursday evening with dry weather expected

No snow expected as snow levels will be above 8000` for the
duration of this event.

.LONG TERM (SAT-TUE)...20/123 PM.

Expecting dry but cool conditions Saturday with some breezy
northwest winds possible. A trough will pass north of the area
Saturday night and there is a little moisture with it but mainly
north of SLO County. May have to introduce some slight chance pops
north of Pt Conception as we get closer but for now it looks too
weak to generate any precip in our area. Gradients will start to
turn offshore early next week, though models differing on the
strength and amount of upper support. Pretty high confidence in a
dry forecast but low confidence on possible Santa Ana winds and
how much warm up we`ll see.



At 1703Z, there was a surface based inversion at KLAX. The top of
the inversion was 1800 feet with a temperature of 14 degrees

Moderate confidence in 18Z TAF package. Rain will gradually
spread south and east across TAF sites through the period with
MVFR/IFR conditions likely with steady rain. However, confidence
in timing of development of rain and associated flight
restrictions is low.

KLAX...moderate confidence in 18Z TAF. High confidence in VFR
conditions 18Z-04Z. High confidence in rain developing tonight,
but low confidence in timing (+/- 4 hours of current 08Z forecast)
and associated MVFR conditions.

KBUR...moderate confidence in 18Z TAF. High confidence in VFR
conditions 18Z-04Z. High confidence in rain developing tonight,
but low confidence in timing (+/- 4 hours of current 08Z forecast)
and associated MVFR conditions.


.MARINE...20/101 PM.

For the Outer Waters, good confidence in current forecast. There
is an 80% chance of Small Craft Advisory (SCA) level southeasterly
winds today through Wednesday night. For Thursday through
Saturday, there is a 70% chance of SCA level west to northwest

For the Inner Waters, good confidence in current forecast. For the
waters north of Point Sal, there is a 70% chance of SCA level
southeasterly winds today through Wednesday evening then a 60% of
SCA level northwest winds Friday/Saturday. For the waters south of
Point Conception, there is a 40% chance of SCA level southeast
winds this evening through Wednesday evening. For Friday and
Saturday, there is a 50% chance of SCA level westerly winds.


CA...Flash Flood Watch in effect from 5 PM PDT this afternoon
      through Thursday afternoon for zones 34-36-39-40-44-51>53. (See LAXFFALOX).
     Flash Flood Watch in effect from Wednesday evening through
      late Thursday night for zones 41-46-54-88-547. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 3 PM PDT Wednesday for
      zones 645-670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 PM this evening to 3 PM
      PDT Wednesday for zone 676. (See LAXMWWLOX).



No significant hazards expected.



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