Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 220100

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
600 PM PDT Wed Mar 21 2018

.SYNOPSIS...21/600 PM.

A strong storm will continue to move over the region and bring
waves of significant precipitation to the region through early
Friday. This could result in debris flows at all recent burn areas
as well as periods of urban and small stream flooding. The threat
of heavy rainfall and a chance of isolated thunderstorms will
continue through Thursday afternoon. Notable snowfall will remain
above 9000 feet.


.SHORT TERM (TDY-SAT)...21/133 PM.

There`s been a little lull overall in the rainfall intensities
this afternoon, though still some pockets of heavier rain
around. Looking at satellite and radar another increase in
rain coverage and intensity is just off the coast and aiming
primarily for SB and SLO Counties and models seem to have a good
handle on this feature showing rain ramping back up through early
evening. Overnight models have been consistent showing the
moisture plume shifting north into SLO County with rain
diminishing temporarily in the south. In fact, all the operational
models show a very strong burst of rain across northwest SLO
County late tonight, possibly associated with the convection now
occurring near 27n/129w (roughly 600 miles southwest of Pt
Conception). Will need to closely monitor that feature as rainfall
rates of an inch per hour or higher are certainly possible.

Thursday morning low level winds are expected to back to the south
and increase quite a bit as the trough and cold approaches. At the
same time the moisture plume will shift back south and the
combination of those factors will bring a return of very heavy
rain to SB and Ventura Counties and by early afternoon LA County.
In fact, rainfall rates during this time are expected to be higher
than they were today as the orographic effects will be much
stronger and there will be much better atmospheric forcing with
the cold front and possibly even some isolated thunderstorms,
though model soundings were decidedly unimpressive with the
stability parameters. Once again rain rates of an inch per hour or
higher are possible during this period and debris flows likely
near burn areas.

Rain expected to start decreasing from west to east Thursday
afternoon and finally exiting LA County early Friday morning.
Models show a weak trough moving into northern California Saturday
but seriously lacking moisture. Still the trough is deep enough
that a few very light showers can`t be ruled out north of Pt

.LONG TERM (SUN-WED)...21/142 PM.

The trough that moves through Saturday is now expected to evolve
into a cut off low near Las Vegas Tuesday with northerly flow
developing behind it. It should remain dry as the trajectory isn`t
favorable for moisture but still uncertain how much offshore flow
we`ll see. Models have definitely trended cooler as the low now is
farther west and we`ll likely see some gusty north to northeast
winds at times through mid week but below advisory levels at this
point. Temps will warm up at lower elevations but remain cool
farther inland.



At 23Z, there was no marine inversion at KLAX.

Moderate confidence in the current forecast. MVFR to VFR
conditions with ceilings below 5000 feet are likely throughout
the period. Periods of IFR conditions are likely in heavier
rainfall. There is a possibility of moderate wind shear and
turbulence after 14Z.

KLAX...VFR conditions with ceilings below 5000 feet will
deteriorate to MVFR between 04Z and 07Z. There is a 50 percent
chance of IFR conditions in heavier rainfall after 16Z,
increasing to 60 percent around 23Z. East winds greater than 7
knots are likely through 14Z, possibly increasing to greater 10
knots after 16Z. There is a 30 percent chance of southerly winds
between 10 and 20 knots between 18Z and 23Z.

KBUR...VFR conditions with ceilings below 5000 feet will
deteriorate to MVFR between 04Z and 07Z. There is a 50 percent
chance of IFR conditions in heavier rainfall after 16Z,
increasing to 60 percent around 23Z. There is a 10 percent chance
of moderate wind shear and turbulence around 23Z.


.MARINE...21/1235 PM.

SCA gusty south to southeast winds will continue into Thursday for
the Outer Waters and Inner Waters north of Point Sal as well as a
SCA for the western portions of the Santa Barbara Channel through
tonight. There is a 20 percent chance of reaching Gale force
winds for the Outer Waters sometime this evening into Thursday
morning. Isolated thunderstorms are possible at times across the
waters through Thursday evening. Brief gusty and erratic winds
with an isolated water spout is possible near any thunderstorm.

SCA winds are likely again late Friday into this weekend across
the Outer Waters with a 30 percent chance of reaching the inner
waters at times. There is also a 20 percent chance of Gale force
winds across the Outer Waters by Sunday.


CA...Flash Flood Watch in effect through Thursday afternoon for
      zones 34-36-37-39-40-44-51>53. (See LAXFFALOX).
     Flash Flood Watch in effect from 11 PM PDT this evening
      through late Thursday night for zones 41-46-54-88-547. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 645-650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT Thursday for
      zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Friday for zone
      673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Thursday for
      zone 676. (See LAXMWWLOX).



No significant hazards expected.



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