Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 191213
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
413 AM PST Thu Jan 19 2017

.SYNOPSIS...
A series of storms will bring rain and mountain snow, heavy at
times, a slight chance of thunderstorms, and strong, gusty
southerly winds to southwestern California through early next
week. Todays storm will diminish through the day. The next
weather system will move through the area Friday. After a brief
lull Saturday a third storm will move in late Saturday night into
early Monday, which should bring the heaviest precipitation
amounts. Temperatures will be below normal across the area into
next week.

&&

.SHORT TERM...(TDY-SAT)

Storm number 1 is half way through L.A. county and will be out of
the area by mid morning. Rain will turn to showers later in the
morning. There is just enough instability behind the front to
justify a slight chc of TSTMs for the LA county area this morning
and afternoon. Right now it looks like this system is putting out
just a little more rainfall than previously thought with most
coastal and vly areas receiving between and inch and an inch of
half of rain.

There will be a brief respite this evening before storm number 2
makes its approach.

Storm number 2 will be a more dynamic and windy system as it will
be powered by a 140 kt jet that will lie atop of Srn Ca during the
period. Heavy rain will develop over SLO county around dawn and
then quickly spread all the way down to L.A. county by late
morning. There is enough energy to create a thunderstorm just
about anywhere. Snow levels will fall to 5000 feet or lower and
there will be pretty impressive snowfall amounts above 6000 feet
this heavy snow and the strong winds will combine to create winter
storm warning conditions.

Rainfall rates will be high enough to create flash flooding
concerns for the burn areas and another flash flood watch for the
burn areas is all but certain. Rainfall amounts with this storm
will be a little higher than today`s numbers. The coasts and vlys
should see between 1 and 2 inches of rain with higher amounts
across the coastal foothills and much higher numbers over the NW
tip of SLO county.

The main trof will move through the area by early evening and the
showers will decrease. There will still be plenty of moisture
below and jet dynamics overhead so the threat of showers will
persist overnight.

There will be a little drying out period on Saturday as a ridge
pops up ahead of storm number three. There may be a shower or two
across the central coast but for the most part it will be dry.

.LONG TERM...(SUN-WED)

Storm number 3 is still looking like the most potent of the 3.
Mdls now agree on the faster timing of this storm, Once again a
powerful jet will set up over the area and provide plenty of
energy to fuel this storm. Light rain will start over the Central
Coast Saturday evening. The light rain will spread south of Point
Conception after midnight while the heavier rain moves into the
Central Coast. Right now it looks like very heavy rain will affect
the Central Coast Sunday morning and then areas south of Point
Conception during the afternoon. The jet will push the heavier
rain out of the rain in the early evening. Rain will turn to
showers during the evening and then diminish some overnight.

As it is forecast now this system at its peak will be able to put
out rainfall rates capable if creating flash flooding in all the
burn areas. Early rainfall estimates for this storm call for 1 to
3 inches across the coasts and vlys with more (much more if the
GFS south wind solution comes to pass) across the coasts and vlys
and a little less across the interior.

The snow level forecast for this system will be tricky esp this
far out. It will depend on how much southerly flow there is. Right
now snow level forecast is at 6000 feet but this could be a couple
thousand feet higher if there are strong south winds.

There will be plenty of clouds and some lingering showers on
Monday.

Dry but cool NW flow will keep things dry but with below normal
temps for both Tue and Wed. Past that it looks like it will be dry
for a while.

&&

.AVIATION...19/1200Z.

Frontal system across eastern Ventura County will sweep
across Los Angeles County early this morning. Widespread low MVFR
to IFR cigs with moderate to heavy rain across L.A. County will
cont through mid morning. There is a slight chance of tstms
across L.A. county through mid morning. There will be a period of
gusty southeast winds ahead of and with the front across L.A.
County early this morning.

Across the remainder of the region behind the front, conds were
mostly high MVFR to VFR...although there will be local IFR conds
through mid morning. These improving conds will spread into L.A.
County by late morning. Occasionally gusty west winds will affect
coastal areas and the Antelope Valley this afternoon. Scattered
showers will persist into the evening hours. Clouds will lower
again tonight as the next front approaches the region and rain
will overspread SLO and SBA Counties by late tonight.

KLAX...Low to moderate confidence in the 12Z TAF. Expect low MVFR
to IFR conds through mid morning with moderate to heavy rain, then
mostly MVFR conds through noon and mostly VFR conds through late
tonight. There is a 30 percent chance that east to southeast
winds could reach 12 to 14 kt through 16z.

With the next front late tonight, there is a 20 to 30 percent
chance that east winds will exceed 10 kt as early as 12z Fri.
There is a 20 percent chance of tstms through 16z.

KBUR...Low to moderate confidence in the 12Z TAF. Expect low MVFR
to IFR conds through mid morning with moderate to heavy rain, then
mostly MVFR conds through noon and mostly VFR conds through late
tonight. There is a 30 percent chance that MVFR conds will
continue through the afternoon. There is a 20 percent chance of
tstms through 16z.

&&

.MARINE...18/900 PM.

Southeast to south winds will continue to increase tonight across all
coastal waters ahead of a cold front. Gales are forecast for the
coastal waters northwest of the Channel Islands through early
Thursday morning. Winds will turn to the west and diminish some
between early Thursday morning and Thursday evening. There is a 40
percent chance that small craft advisory headlines may need to be
extended into Thursday night. Winds will increase again early
Friday across the entire coastal waters and remain elevated
through at least Saturday. A gale watch remains in effect for the
entire coastal waters from early Friday morning through Saturday
night. There is a slight chance of thunderstorms tonight into
Thursday and again on Friday.

A large long period swell will build across the coastal waters
through Thursday, then continue to build to very large levels
Friday night into Saturday. The swell will likely reach heights
of more than 20 feet over the northern outer waters late Friday
night into Saturday. West-to-northwest facing bays and harbors
may be impacted by the swell over the next coming days,
especially Morro Bay and Ventura Harbors.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 9 PM PST Tuesday for zones
      34-35. (See LAXCFWLOX).
     High Surf Advisory in effect from 4 PM this afternoon to 9 PM
      PST Tuesday for zones 39>41-87. (See LAXCFWLOX).
     Winter Storm Warning in effect until 9 AM PST Saturday for
      zones 53-54. (See LAXWSWLOX).
     Flash Flood Watch in effect until 10 AM PST this morning for
      zones 54-88. (See LAXFFALOX).
     Wind Advisory in effect until 10 AM PST this morning for zone
      59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Friday for
      zones 645-670-673-676. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM to 9 PM PST Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 10 AM PST Friday for
      zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 10 AM to 9 PM PST Friday for
      zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 3 AM Friday to 3 AM PST Saturday
      for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(SAT-WED)
For Saturday, very large and potentially damaging surf will likely
impact west-facing beaches. Minor coastal flooding is also
possible Saturday morning. There could also be some lingering
mountain snow showers on Saturday morning, with potential impacts
on the Interstate 5 corridor going over the Grapevine.

Another storm system will impact the region late Saturday night
through Monday. Potential impacts include flash flooding and
debris flows for the burn areas, urban and small stream flooding,
rock slides along canyons roads, downed trees and isolated power
outages, significant travel delays, and dangerous winter driving
conditions in the mountains.

&&

$$

PUBLIC...Rorke
AVIATION...DB
MARINE...Hall
SYNOPSIS...Sirard

weather.gov/losangeles


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