Area Forecast Discussion
Issued by NWS Los Angeles, CA

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423
FXUS66 KLOX 211637
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
837 AM PST Tue Feb 21 2017

.SYNOPSIS...
Light rain will linger today. A low will move into Nevada tonight
with breezy north winds and possible precipitation for the
mountains through Wednesday night. The clouds will decrease into
Friday...and temperatures should be about normal by the weekend.
A storm should approach from the north on Saturday and spread
precipitation by Sunday. The precipitation could continue into
Monday.

&&

.SHORT TERM...(TDY-THU)

A narrow band of mid-to-upper level moisture is showing up well
on radar right now over Los Angeles County. While the radar looks
more ominous than it is (being high based) it is a bit of a
surprise, and leads to a better chance for some light but
measurable rain (under 0.10 inches) for LA County. Upped PoPs as
a result. To the north, low level moisture is interacting with the
southwest flow aloft once again today. Radar for SLO to Ventura
Counties is showing some low reflectivities, but this is very much
under- representing the rain because the moisture is so close to
the ground. With steady light rain falling there now, upped PoPs
to near 100 percent...though additional amounts will be light and
mainly in the 0.10 to 0.25 inch neighborhood. The low- level
nature of this rain will also make interior areas hard pressed to
get rain as the mountains will block a lot of it, but a few
showers could squeeze through. Rain still looks good to taper off
quickly later today and tonight...but low confidence on exactly
when as it could quickly shut off this afternoon or linger into
the evening.

***From Previous Discussion***

An inside slider moves down the CA/NV line tonight. It is pretty
dry but it will shift the winds to the north which will pile up
clouds and a few showers on the north slopes. Otherwise skies
should turn partly cloudy across the coasts and vlys. Despite the
additional sunshine the max temps will fall a couple of degrees as
cold air filters in behind the trof. the winds will keep the
clouds and scattered showers going through the day. Snow levels
will fall through the day but should remain above the Grapevine
pass level.

It looks like advisory level wind gusts will develop across the LA
VTA and SBA mountains as well as the Antelope Vly Wednesday night.
The winds will be strongest through the i-5 corridor. It will also
be gusty in the Santa Clarita Vly and the area either side of the
VTA/LA county border. Clouds and a few showers will remain on the
north slopes. Snow levels will get close to the pass levels.

The barest of ridges will move into the area Thursday. Skies will
be mostly sunny. It will remain breezy but right now it looks like
the winds will be below advisory criteria. Max temps will warm a
couple of degrees but will still be below normal.

.LONG TERM...(FRI-MON)

Both the GFS and the EC agree that dry zonal flow will be over the
state on Friday and Saturday. Skies will be mostly clear
Friday...but Saturday will see a slow increase in clouds as a new
system begins its run into the state. Max temps will increase each
day and Saturday will be the warmest of the next 7 with max temps
coming in only a degree or two below normals.

Both the EC and the GFS are in fair agreement that a cool upper
low embedded in the base of it much larger parent trof will rotate
down the coast and then into the center of the state. If the
current mdl forecast is right light rain will overspread the area
Saturday night. The cold front with moderate rain will move over
the area during the day Sunday. Showers will then move in behind
the front and keep the area wet Sunday night and Monday. Would
like to see a few more mdl runs before fully jumping on this rain
bandwagon as frequently there are changes to both timing and
intensity of these storms as the event draws closer.

&&

.AVIATION...21/1040Z...

At 1030Z, there was no marine inversion at KLAX.

Overall, low confidence in 12Z TAF package as light rain
is expected through this afternoon with CIGs and VSBYs likely to
bounce between multiple flight categories. For tonight, 50/50
chance of MVFR or VFR conditions prevailing at all coastal and
valleys TAF sites.

KLAX...low confidence in 12Z TAF. Moderate confidence in
development of MVFR conditions this afternoon (after 14Z), but low
confidence in MVFR conditions continuing through tonight (50%
chance of VFR developing after 20Z). Any east winds should remain
below 7 knots this morning.

KBUR...low confidence in 12Z TAF. Moderate confidence in
development of MVFR conditions this afternoon (after 14Z), but low
confidence in MVFR conditions continuing through tonight (50%
chance of VFR developing after 20Z). There is a 30% chance of
IFR CIGs 16Z-22Z.

&&

.MARINE...21/130 AM...

For the Outer Waters, high confidence in current forecast. Through
tonight, Small Craft Advisory (SCA) level seas will persist.
During the day on Wednesday, northwest winds will increase to SCA
level and persist through Thursday night. On Friday, northwest
winds are expected to drop below SCA levels. However on Saturday,
southerly winds are expected to develop, reaching SCA levels.

For the Inner Waters, moderate to high confidence in current
forecast. For the waters north of Point Sal,SCA level seas will
persist. During the day on Wednesday, northwest winds will
increase to SCA level and persist through Thursday night. On
Friday, northwest winds are expected to drop below SCA levels.
However on Saturday, southerly winds are expected to develop,
reaching SCA levels. For the waters south of Point Conception,
winds and seas are expected to remain below SCA levels through
tonight. From Wednesday through Thursday night, west to northwest
winds are expected to increase to SCA levels, especially across
western sections. By Friday and Saturday, winds will drop below
SCA levels.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 4 PM PST this afternoon
      for zones 34-35. (See LAXCFWLOX).
PZ...Small Craft Advisory for hazardous seas in effect until 3 AM
      PST Wednesday for zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(THU-MON)
Snow levels below 4,000 feet Wednesday night could result in
light snow mountain and interior valley roads including the Tejon
Pass. Gusty north winds are expected Wednesday and Thursday which
will create hazardous road conditions and possible downed trees.
More rain and wind is expected over the weekend.

&&

$$

PUBLIC...Kittell/Rorke
AVIATION...RAT
MARINE...RAT
SYNOPSIS...STu

weather.gov/losangeles



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