Scientific Forecaster Discussion
fxus66 klox 182149
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
149 PM PST Thu Jan 18 2018
a cold and fast moving storm system will bring much cooler
temperatures...gusty winds...and light rain and mountain snow
showers to the region by Friday. Snow showers will linger into
Saturday morning across the northern slopes. Warmer conditions
return next week, but there is a slight threat of a few showers
across the northern portion of the forecast area early next week.
Tightly wound upper low continues to spin off the British Columbia coast while a
weakening cold front makes it way southeast through California.
Very little in the way of dynamics or orographic lift with this
initial feature so precip expected to be light and spotty,
especially south of pt Conception where many places likely will
struggle to even get .01 out of it. Slightly higher amounts across
slo/sba counties but I expect most areas to check in with a tenth
Following the cold front will be the upper low which will bring
more in the way of dynamics late Friday into Saturday but by then
a good portion of the moisture has moved east with the initial
frontal band. The exception being the north facing slopes near the
Kern County line and the Grapevine where moisture will bank up
against the mountains as strong northwest flow develops. At the
same time much colder air will drop snow levels to around 3000' by
Friday night and likely create some hazardous driving conditions
over the Grapevine on Interstate 5. Could see 1-3" of accumulation
on or around the Interstate into Saturday morning. That combined
with wind gusts of 50+ mph will make for a very hazardous drive
through the mountains. The northwest flow and diminishing
moisture will likely result in a substantial decrease in clouds
and shower activity elsewhere by Friday evening but with gusty
west to northwest winds that may reach advisory levels near the
coast and in parts of the Antelope Valley. A little bit of
instability over the coastal waters west of pt Conception late
Friday and will keep the small chance of thunderstorms out there.
Cool, dry, and breezy over the weekend after the last of the mtn
showers taper off Saturday.
Slow warming trend early next week as a ridge starts to build over
the area. Both the GFS and European model (ecmwf) show the tail end of another weak
front coming through the area Monday but any precipitation should
be confined to nrn slo County at best. Elsewhere just some mid and
high clouds. Poor agreement in the models mid to late next week
with the possibility of another weak system for either Wed or Thu
but again very low confidence. None of the model solutions in the
last few days have indicated anything more than a very light
precip event at best, and mostly northern areas. Then dry and
warmer going into next weekend.
At 1645z, there was a surface-based inversion at klax. The top of
the inversion was 1200 feet with a temperature of 21 degrees
Overall, moderate confidence in 18z taf package. Through early
this evening, high confidence in VFR conditions for all sites. For
tonight/Friday morning, weak system will move across the area.
Stratus/fog should increase with MVFR cigs/vsbys for all coastal
and valley sites, but confidence in timing of development of
flight restrictions is low. There is a chance of some light
showers/patchy drizzle after 08z for all areas west of the
Klax...moderate confidence in 18z taf. High confidence in VFR
conditions through this evening. For late this evening through
Friday morning, high confidence in MVFR conditions developing, but
low confidence in timing (+/- 4 hours of current 06z forecast).
There could be some patchy drizzle after 08z.
Kbur...moderate confidence in 18z taf. High confidence in VFR
conditions through this evening. For tonight/Friday morning, high
confidence in development of MVFR conditions, but low confidence
in timing (+/- 4 hours of current 09z forecast). There could be
some patchy drizzle after 08z.
For the outer waters, moderate to high confidence in current
forecast. High confidence in Small Craft Advisory (sca) level
conditions through Friday morning due to hazardous seas, with Small Craft Advisory
level winds in many areas as well.
Very large northwest swell overspread the waters today, and peak tonight
and Fri morning, with combined seas of 15-19 feet. Northwest winds will
increase Fri. There is a 50% chance of gale force winds Fri
afternoon thru Sat evening across the southern two zones (pzz673,
pzz676) and a 20% chance of gales across the northern zone
For the inner waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, high confidence in
Small Craft Advisory (sca) level conditions due to hazardous seas
through tonight, then winds and seas Fri thru Sat evening. There
is a 20% chance of gale force winds Fri afternoon and Fri night.
Across the sba channel and the southern inner waters, west swell
will build tonight and Friday. There is a 40-50% chance of gale
force winds Fri afternoon thru Sat. Gale watches are in effect,
but confidence is not high enough to upgrade to warnings at this
time. There is a good chance that a Small Craft Advisory will be needed as early as
late tonight or Fri morning, due to hazardous seas and/or winds.
Dangerous breaking waves are possible near Harbor entrances,
including morro beach Harbor and Ventura Harbor through Saturday
An extended period of large surf is expected along west and
northwest facing beaches through Saturday evening as very
large westerly swells move through the coastal waters.
For west and northwest facing beaches along the central coast,
surf will build today, peak at 15 to 20 feet with local sets to
25 feet this afternoon or evening through Saturday before slowly
subsiding. A high surf warning remains in effect from this
afternoon through 900 PM PST Saturday evening. The high surf may
cause beach erosion and will produce life-threatening rip
currents. Minor coastal flooding is possible in low lying areas
such as parking lots, especially near the times of high tide.
For west and northwest facing beaches south of Point Conception,
surf will build today, then peak at 8 to 12 feet by late tonight
and Friday. Local sets to 15 feet are possible on exposed west
facing locations such as Ventura Harbor. High surf will continue
through Saturday evening before slowly subsiding. A high surf
advisory remains in effect through 900 PM PST Saturday evening.
California...high surf warning in effect until 9 PM PST Saturday for zones
34-35. (See laxcfwlox).
Winter Weather Advisory in effect from 10 am Friday to 4 PM
PST Saturday for zones 38-52>54. (See laxwswlox).
Beach hazards statement in effect through Saturday evening
for zone 39. (See laxcfwlox).
High surf advisory in effect until 9 PM PST Saturday for
zones 40-41-87. (See laxcfwlox).
Pz...Small Craft Advisory in effect until 3 am PST Sunday for
zones 645-670. (See laxmwwlox).
Gale watch in effect from Friday afternoon through Saturday
evening for zones 650-655-673-676. (See laxmwwlox).
Small Craft Advisory in effect until 1 PM PST Friday for
zones 673-676. (See laxmwwlox).
Hazard potential outlook...(sun-thu)
no significant hazards expected.