Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 110057
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
457 PM PST Sat Dec 10 2016
A chance of light rain will continue through Sunday morning, with
the best chance of rain on the Central Coast. Dry weather is
expected Sunday afternoon and Monday. Rain could return to the
Central Coast by Tuesday, then possibly the entire area late next
week as a stronger low pressure system develops. Near or slightly
below normal temperatures are expected through next week.
Stubborn low clouds and fog remained along the coast and into some
vlys s of Pt Conception early this afternoon. There was also patchy
drizzle noted along the coast. Otherwise, partly cloudy skies
covered VTU/L.A. Counties early this afternoon. It looks like the low
clouds will expand into the San Fernando and San Gabriel Valleys
thru sunset while elsewhere the partly cloudy skies should continue.
For SLO/SBA Counties, mostly cloudy skies were noted and some
showers started to develop along the Central Coast as a cold front
approached from the n. Some gusty nw winds will persist over higher
terrain and in the Antelope Valley thru the afternoon as well. Temps
across the region will be several degrees below normal for the coast
and vlys, and several degrees above normal for the mtns and deserts.
Highs will be in the mid 60s to near 70 in the warmest vlys and
coastal areas this afternoon.
A flat upper level ridge will linger over srn CA today. A weak
impulse will lower 500 mb heights tonight from around 580 dm to 575
dm or so, with little change expected Sun thru Tue. A broad mainly
westerly flow aloft will persist through Mon, then turn more
southwesterly for Tue.
A weak surface cold front is forecast to sag south from central CA
into SLO/SBA Counties tonight then dissipate as it moves further s
on Sun. This front will bring cloudiness and widespread light rain
to SLO/SBA Counties tonight then taper off to scattered showers by
Sun morning. There will also be a chance of rain mainly on the n mtn
slopes of VTU/L.A. Counties during the period. This front will be
accompanied with nw flow thru the lower levels which should limit
the rain from moving s of the mtns over VTU/L.A. Counties, altho
there should still be a slight chance of pcpn for the coast and vlys
later tonight into Sun morning.
Rainfall will be light over the region tonight thru Sun morning,
with about 0.05 to 0.15 inch expected for SLO/SBA Counties and the n
mtn slopes of VTU/L.A. Counties, except up to 0.25 inch cannot be
ruled out in far nwrn SLO County. Elsewhere over VTU/L.A. Counties,
0.05 inch or less can be expected, with many locations probably
receiving little if any pcpn at all.
Lingering moisture at mid and upper levels will continue to move in
from the w Sun afternoon thru Mon night which should keep partly
cloudy skies as a whole over the area. However, the 12Z NAM was
indicating plenty of moisture below 2000 ft with a weak eddy Sun
night into Mon morning s of Point Conception, with low clouds and
fog possible for the coast and vlys of VTU/L.A. Counties. Low clouds
and fog will again be possible for the VTU/L.A. County coast and
vlys Mon night into Tue morning as well.
A weak upper level disturbance and surface wx system is forecast to
approach the central CA coast on Tue, with a warm front extending to
the Central Coast. Increasing clouds with a chance to slight chance
of rain can be expected over much of SLO/SBA Counties on Tue, with
the best chance of rain in the afternoon. Dry weather with partly
cloudy skies will prevail over VTU/L.A. Counties on Tue.
Temps on Sun are forecast to remain several degrees below normal for
the coast and vlys and a few degrees above normal for the mtns and
Antelope Vly. Temps should warm slightly overall for Mon and Tue,
with highs near normal to slightly below normal for the coast and
vlys, and 4 to 10 deg above normal in the mtns and deserts. Highs in
the warmest vlys and coastal areas should reach the mid to upper 60s
on Sun, and upper 60s to around 70 for Mon and Tue.
The GFS and EC are in reasonably good agreement with synoptic scale
features Wed and Thu, then start to show some differences Fri and
Sat altho these differences will probably not make much difference
in the overall forecast for southwestern CA. Overall, went with a
blend of the two models for this forecast period. A broad upper
level trof will be over the e Pac on Wed then approach the w coast
on Wed night before moving into CA on Thu. Persistent upper level
troffing can be expected along and off the CA coast Thu night and
Fri, with the main upper trof pushing to the e on Sat. The GFS is a
bit deeper then the EC with regards to the upper trof along and off
the CA coast on Fri.
A chance of rain will continue over SLO/SBA Counties Wed into Wed
evening as the warm front persists along the Central Coast. A
surface low pressure system over the e Pac will move into Central CA
by early Thu morning, with a cold front expected to pass through
swrn CA later Thu and Thu evening with rain likely across much of
the forecast area. The rain will taper off Thu night with lingering
widely scattered showers expected over the area Fri and Fri night.
Dry weather can be expected over the area on Sat. There is fairly hi
confidence the weather system will affect the area on Thu into Thu
night, with the potential for significant rain and gusty winds. Snow
levels will be high on Thu then lower quickly Thu night, with a
potential for snow showers down to 6500 to 7000 ft by late Thu
night, altho could be even lower. Any significant accumulating snow
in the mountains should be at or above resort levels with this
weather system. There is still some uncertainties with the exact
timing and intensity of this storm system, as well as how quickly
the cold air will move in late this week. However, temps will likely
turn sharply cooler for Fri and Sat, and be well below normal in all
areas. Colder vlys will likely have frosts and freezes Fri night
into Sat morning as well.
At 00Z, at KLAX, the marine layer was around 1000 ft deep. The top
of the inversion was near 1500 feet with a temperature around 14
degrees Celsius. There was secondary inversion above...up to 4000
Low to moderate confidence in the current forecast. Sub-VFR
conditions, likely in the IFR to MVFR category, are expected
through at least 18Z. There is a chance of VLIFR to LIFR
conditions through 15Z. There is a chance of VFR conditions after
KLAX and KBUR...MVFR conditions should deteriorate to IFR after
05Z. There is a 30 percent chance of LIFR conditions between 10Z
and 14Z. There is a 50 percent chance of VFR conditions after 18Z.
Moderate confidence that gusty west winds (around 25 KT) and/or
short period steep seas (4-6 feet at 6-8 seconds) will reach the
lower end of Small Craft Advisory (SCA) criteria across the
southern two thirds of the outer waters, and at least western
portions of the southern inner waters (Santa Barbara Channel and
Santa Monica Basin) later through tonight. Patchy dense fog will
also be around through at least Sunday morning, but very
difficult to forecast exactly where.
Winds should decrease some late tonight, but there is a 60 percent
chance for low-level SCA NW winds from the Central Coast to San
Nicolas Island Sunday afternoon and night. Choppy short-period
seas will likely continue everywhere through at least Monday, but
should be smaller than tonight. There is a chance for a strong
storm system on Thursday or Friday of next week.
PZ...Small Craft Advisory in effect until 3 AM PST Sunday for
zones 650-655-673-676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK...(TUE-SAT)
There is the potential for widespread rains and gusty winds later
next week. Still considerable uncertainty in timing and amounts
from this storm, but most likely impacting the area sometime
between Thursday and Thursday night. There is the potential for a
cold and unsettled pattern lingering Friday and Friday night, with
a threat of rain showers and mountain snow showers.