Area Forecast Discussion
Issued by NWS Los Angeles, CA

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254
FXUS66 KLOX 162329
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
329 PM PST Mon Jan 16 2017

.SYNOPSIS...
Offshore flow and mild weather will continue through the middle of
the week. Rain and mountain snow can be expected late in the week,
as a couple of low pressure systems approaching from the northwest
affect the region. Unsettled weather may continue through next
weekend.

&&

.SHORT TERM...(TDY-THU)

Overall, 12Z models are in good agreement through the short term
period. At upper levels, ridge will nose across Central California
tonight and Tuesday then a very cold low will push towards the
Pacific Northwest Wednesday/Thursday. Near the surface, weak
offshore flow will prevail through Tuesday then south/southwest
flow develops Wednesday/Thursday.

Forecast-wise, no major changes to the current forecast thinking.
With ridge overhead and weak offshore flow, tonight and Tuesday
will be mostly clear as offshore flow prevents any low cloud
development. Upper-level support is weak and gradients are not too
strong, so any northeasterly winds that develop should remain
below advisory-levels through Tuesday. However, the offshore flow
will allow for temperatures to warm to seasonal levels, if not a
degree or two warmer on Tuesday.

For Tuesday night and Wednesday, flow will shift to southwesterly
and an eddy is forecast to develop over the bight. So, will expect
some redevelopment of low clouds Tuesday night/Wednesday morning
(although confidence in coverage of low clouds is still low).
Additionally, there will be increasing mid/high level clouds
during the day on Wednesday in advance of first storm forecast to
impact the area. With increasing clouds and onshore flow,
Wednesday will be a cooler day.

For Wednesday night and Thursday, the first storm will roll across
the area. Rain will begin across the Central Coast Wednesday
evening and across Ventura/Los Angeles counties after midnight
with rain exiting Los Angeles county by Thursday afternoon.
Scattered showers will be possible Thursday afternoon just about
anywhere. 12Z model data still consistent, indicating generally
0.25 to 0.75 inches of rainfall with this storm (with locally
higher amounts in favored upslope areas). Rainfall intensities do
not look too impressive, so do not anticipate any major problems
for the recent burn areas with this first storm. Snow levels will
start out above 8000 feet on Wednesday, but will drop to around
5000 feet during the day on Thursday. There will likely be a few
inches of snow accumulation at the resort level and some type of
winter weather product may be needed as the event draws closer.

.LONG TERM...(FRI-MON)

Overall, 12Z models remain consistent and in pretty good agreement
through the period as a very unsettled pattern will persist across
southwestern California.

On Friday, the second in the series of storms will sweep across
the area. Rain should begin across the Central Coast early Friday
morning then spread southward across Ventura/Los Angeles counties
during the day, exiting Los Angeles county by late afternoon with
scattered showers possible Friday night and Saturday. This system
looks to be a bit more potent on all models (especially the GFS)
as stronger southerly flow ahead of the front will help with
orographic enhancement of the rainfall. At this time, rainfall
estimates are for between 0.50 and 1.50 inches (with local amounts
up to 2.50 inches possible in the more favored upslope areas).
Rainfall intensities with this storm could reach problematic
levels for the recent burn area. As for snow, this storm looks to
be a bit colder. Snow levels will start out around 5000 feet
Friday morning, but will drop to between 3500 and 4000 feet Friday
night and Saturday. Snowfall accumulations will likely be more
impressive with accumulating snowfall at lower elevations than the
Thursday storm.

For Sunday and Monday, the wet and unsettled weather will
continue. Both the GFS and ECMWF move a third storm across the
area on Sunday which could be even more potent than Friday`s
storm. For Monday, the model solutions do diverge as the GFS
brings another storm across the area while the ECMWF just keeps a
showery pattern over the area. Either way, there is the distinct
possibility of Sunday/Monday being the most impressive of all the
storms over the next 7 days.

&&

.AVIATION...16/2330Z...

At 2330z at KLAX... there was a weak inversion around 700 feet.
The top of the inversion was around 1500 feet with a temperature
of 13.5 degrees celsius.

High confidence in the 00z TAFs. Increasing low level offshore
flow overnight into Tuesday morning should keep TAF sites VFR
through period. Only concern will be low clouds and fog possibly
spilling into KPRB from the east, but only a 20 percent chance.
There is a 10 percent chance of mvfr cigs redeveloping at KLAX
and KLGB tonight.

KLAX...High confidence in the 00z TAF. VFR conditions expected
through period. Only a 10 percent chance of MVFR cigs redevelopingovernight.
Light northeast to east winds expected to develop overnight into
Tuesday morning, but speeds expected to remain below 6 knots.

KBUR...High confidence in VFR conditions through period.

&&

.MARINE...16/200 PM...

For all of the Outer Waters and for the Inner Waters north of Pt
Conception... moderate confidence in the current forecast.
Northwest winds will be below Small Craft Advisory (SCA) levels
today through Wednesday afternoon. Southerly winds will increase
on Wednesday ahead of a frontal system and will reach SCA levels
Wednesday night. SCA conditions will generally persist into the
weekend as another front moves across the waters just as the winds
lessen from the first system. There may be a period of time in
which the winds will fall below advisory criteria between the two
frontal systems.

For the Inner Waters south of Pt Conception... moderate confidence
in the current forecast. Light winds are expected through
Wednesday afternoon then winds will increase on Wednesday ahead
of a frontal system but are likely to remain below SCA levels.
There is a better chance of SCA conditions developing on Friday
ahead of another frontal system.

A fairly large long period swell will affect the waters today
through Tuesday. Another large long period swell arrives in the
region early on Wednesday... then yet another is forecast to
arrive Friday night into Saturday. This third swell of the week
will be the largest... potentially reaching heights of 20 feet at
18 seconds over the northern outer waters late Friday night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Tuesday evening for
      zones 40-41. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
A wet and unsettled weather pattern is likely Wednesday night
through Monday. The heaviest rain during this period will probably
fall on Friday and again later Sunday and Monday. There is a chance
of damaging warning level surf and coastal flooding issues starting
Friday and continuing through Saturday, especially along the
Central Coast.

&&

$$

PUBLIC...RAT
AVIATION...Gomberg
MARINE...Kj
SYNOPSIS...Sweet

weather.gov/losangeles



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