Area Forecast Discussion
Issued by NWS Los Angeles, CA

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736
FXUS66 KLOX 222301
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
301 PM PST Sun Jan 22 2017

.SYNOPSIS...

There will be precipitation...heavy at times...and gusty winds into
this afternoon. This evening the rain will turn to showers...with
a chance of thunderstorms and gusty winds into Monday. There
may still be a chance of showers on Tuesday. The temperatures
should stay below normal into midweek. The skies will become fair
by midweek with normal temperatures on Friday and Saturday.

&&

.SHORT TERM...(TDY-WED)

The latest satellite imagery indicates the main band of the
atmospheric river moving across Ventura and Santa Barbara
Counties currently. Moderate to heavy rainfall continues to fall
across much of Los Angeles and Ventura Counties this afternoon.
The cold front sits just offshore of the Central Coast, while the
main center of the strong trough of low pressure is located near
45N and 130W or about 450 miles west of Seattle. The rain band
will continue to move east across the area through early this
evening. Rainfall rates with the frontal band have underperformed
relative to earlier forecasts, but the overall rainfall amounts
forecast is in good shape and look agreeable with the current
forecast. The storm total forecast looks good with between 2 to 4
inches of rainfall for the coast and valleys and 3 to 6 inches of
rainfall in the foothills and mountains. NCEP High Resolution WRF-
NMM solutions are handling the precipitation amounts well this
afternoon and agreement exists well with the current forecast.
With the more sub-tropical influence with this storm system,
regional radars are overestimating the precipitation amounts and
caution should be exercised.

Colder air aloft with the trough will punch in through this
evening and provide more favorable instability for thunderstorm
development. High resolution model solutions suggest a band of
high intensity showers developing offshore over the next several
hours. With the best jet dynamics and the most unstable air mass
moving, forecast for showers with a chance of thunderstorms seems
the best approach. Orographic lift should enhance as winds remain
south to southwesterly at this time. The flash flood watch has
been extended across the watch area as the best instability will
move in.

With the colder air mass moving in this evening, snow levels
currently between 6000 and 6500 feet this afternoon will fall
overnight to between 3500 to 4000 feet by early Monday morning.
Snow-water ratios will be quite low due to the more tropical
influence from the system, but as the colder and less moist air
mass arrives tonight, snow-water ratios should increase as snow
levels drop. The current winter storm warning looks good with a
mix of heavy accumulating snow and strong winds. Forecast amounts
between 6 to 12 inches of snow is forecast for locations down to
6000 feet. Local amounts up to 18 inches are possible above 7000
feet, but isolated amounts up to two feet cannot be ruled out
across more favored peaks in the San Gabriel Range.

The trough and associated colder air instability will keep the
threat of showers and thunderstorms in the forecast for the next
several days. The latest model solutions keep instability over the
area through Tuesday afternoon or Tuesday evening. While the flash
flood watch remains in effect through Monday afternoon due to
favorable instability for heavy rainfall, there is a chance that
the watch, or portions of the watch could be extended into
Tuesday evening should conditions warrant.

Ridging aloft builds in between Tuesday night and Wednesday
bringing a warming and drying trend into the forecast.

.LONG TERM...(THU-SUN)

Ridging aloft will remain over the area for Wednesday, but models
solutions have added a wrinkle between Wednesday night and
Thursday. Latest model solutions break off a piece of a trough of
low pressure from the trough just south of the Aleutian Islands.
The weak disturbance ejects towards the West Coast late Monday and
arrive Wednesday night. Clouds and PoPs have been increased
slightly for Wednesday night and Thursday, but at the worst, the
storm system will likely only bring rain impacts to the Central
Coast, and bring northerly winds to areas south of Point
Conception.

&&

.AVIATION...22/1800Z.

At 18z at KLAX...there was no marine inversion.

There is generally low confidence in the 18z TAFS. Frequent
changes in the ceiling heights and visibility will be the primary
concerns. The rain was starting to show some signs of slowing down
north of Point Conception...although scattered showers are likely
to continue through Monday. South of Point Conception...the area of
heaviest rain will slowly translate from Ventura county into Los
Angeles county by late this afternoon.

KLAX...Low confidence in the TAF. The reduced confidence is
primarily due frequent changes in ceiling and visibility.
Conditions will range mostly from MVFR to IFR. Winds from 090-130
degrees greater than 7 kts will continue through 00z. There is a
forty percent chance of southerly cross winds greater than 20
knots 23Z-01Z. The winds are expected to shift around to 210-240
degrees after 02z. There is a thirty percent chance of
thunderstorms after 08z.

KBUR...Low confidence in the TAF. The reduced confidence is
primarily due frequent changes in ceiling and visibility.
Conditions will range mostly from MVFR to IFR. There is a thirty
percent chance of thunderstorms after 08z.

&&

.MARINE...22/200 PM.

Very dangerous sea conditions are expected through tonight.

Breaking waves will continue over Morro Bay and Ventura Harbor
entrances as well as near the shoreline and breakwalls. There is
high confidence in a large swell through Tuesday.

High confidence for widespread gale force southerly winds and very
steep seas into the evening for the southern waters. A small craft
advisory is in effect for the northern waters through tonight.
There is a thirty percent chance that Gale Warning conditions
across the southern waters may continue after midnight.

Moderate confidence in thunderstorms forming tonight through
Monday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 6 PM PST Tuesday for zones
      34-35-39>41-87. (See LAXCFWLOX).
     Flash Flood Watch in effect through Monday afternoon for
      zones 34>41-44>46-51>54-59-87-88-547. (See LAXFFALOX).
     Wind Advisory in effect until 6 AM PST Monday for zones
      40-41-44>46-87-88. (See LAXNPWLOX).
     Winter Storm Warning in effect until 6 PM PST Monday for
      zones 52>54. (See LAXWSWLOX).
     High Wind Warning in effect until 7 PM PST this evening for
      zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 1 AM PST Monday for
      zones 645-670-673. (See LAXMWWLOX).
     Gale Warning in effect until 9 PM PST this evening for zones
      650-655-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)

No significant hazards expected at this time.

&&

$$

PUBLIC...Hall
AVIATION...Sweet
MARINE...Sweet
SYNOPSIS...STU

weather.gov/losangeles



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