692 
FXUS66 KLOX 192352 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA 
452 PM PDT Tue Oct 19 2021

updated aviation discussion

.SYNOPSIS...19/905 AM.

Today will be sunny with a noticeable warming trend. Wednesday 
and Thursday will feature more warming and partly to mostly 
cloudy skies along with night through morning low clouds across 
the coastal area. There is a chance of a significant storm in the
Sunday to Monday time period.

&&

.SHORT TERM (TDY-FRI)...19/140 PM.

Synoptically, there is a 542 dam upper low offshore around the 
CA-OR and a weak ridge has built in from the south in the wake of
yesterday's cold front. A trough associated with the upper low will
clip the northern part of our area on Wednesday, bringing a 
slight chance of showers to northwest SLO County. The ridge builds
higher on Thursday and should bring the high temperatures of the 
week, to near normal levels. Ensembles have an impactful storm
system dropping from the Gulf of Alaska and drawing in moisture
from the Pacific and impacting the area primarily Sunday and
Monday.

A weak ridge has moved into the state in the wake of yesterday's
trough passage. Heights will rebound to 576 dam. There will be 
weak offshore flow both from the north and the east in the 
morning. These offshore gradients will reverse in the afternoon to
weak onshore. Skies will be clear since the cool air that spilled
into the area yesterday wiped out the marine inversion. The lack 
of cold air advection will allow the mountains and interior to 
warm 8 to 12 degrees today. The weak offshore flow and delayed 
seabreeze will bring 2 to 5 degrees of warming to the coasts and 
valleys with the exception of the SBA south coast where the lack 
of northerly offshore flow will keep max temps 2 to 5 degrees 
cooler. Despite the warming, max temps will still end up 5 to 10 
degrees below normal.

Onshore flow and weak cyclonic turning will bring marine layer 
stratus back to the coasts later tonight.

On Wednesday a weak front will wash out over Monterey County.
There is a small chance that the NW portion of SLO county could
see a light shower. The onshore push ahead of the front will keep
the low clouds across the beaches through the afternoon. Mid and
upper level clouds embedded in the SW flow aloft will create
partly to mostly cloudy skies over the southern half of the state.
The switch to onshore flow will cool the coast several degrees but
slightly higher heights will allow several degrees of warming for
the interior.

Expecting the marine layer cloud pattern to develop Wednesday 
night and cover most of the coast with low clouds. The beaches 
across the Central Coast will again struggle to clear due to 
better onshore flow slight lift from an approaching trough. Moist
SW flow aloft will persist across the state and there will be 
enough mid level clouds to make the rest of the day partly cloudy 
(maybe a few instances of mostly cloudy - especially over SLO 
county). Heights will continue to rise Thursday and will reach 
582 dam in the afternoon. These height rises, along with weak 
offshore flow from the north, will combine to bring 5 to 10 
degrees of warming to almost all of the area. This will make 
Thursday the warmest day of the next 7 with max temps coming in a 
few degrees either side of their normals.

The ensembles agree that the xtnd periods weather will be 
dominated by a powerful Gulf of Alaska low that will spin off of 
the WA/OR coast before moving across the west coast on Monday. The
first impulse will push into areas north of Pt Conception Friday.
This first impulse does not look that significant and rainfall if
any will be light and concentrated over SLO county (As always the
extreme NW tip of SLO county could see substantial more rainfall 
than the rest of the area). Skies will be mostly cloudy as the 
system washes out over it. Max temps will fall 3 to 6 degrees due 
to falling heights and increased cloud cover.

.LONG TERM (SAT-TUE)...19/157 PM.

Saturday will likely be dry but will remain mostly cloudy with 
perhaps a few periods of partly cloudy skies. Heights will 
continue to fall and max temps will dip another 2 to 5 degrees. 
Coastal and Valley max temps will almost all be in the 60s and 
lower 70s, which is 5 to 10 degrees below normal.

The main impulse from this upper low will primarily affect our
area Sunday and Monday. The upper low will be just to the west of
Coos Bay OR by Sunday afternoon. This location will focus a WSW 
to ENE oriented powerful jet stream over Central and Southern CA.
By Monday morning the area will be under the right front quadrant
of a 130kt jet streak. Model solutions show this system 
entraining a substantial amount of moisture into its flow pattern 
and early PWAT estimates are near 1.7 inches. The exact timing of
this event is still a little murky, but should be between a late 
Sunday to Monday afternoon peak. The most rain will very likely 
fall over the Central Coast. Preliminary rain estimates for the 
two day period from WPC call for about 2 inches of rain for the 
Central Coast and 1 inch for areas South of Pt Conception. As we
have seen over the years, a slight positional difference or
orientation change with respect to our transverse mountains can
have a significant impact on rain amounts. 

By Tuesday the center of the storm should have moved to our east 
but we will still be in a trough so continues cloudy skies are
likely.

&&

.AVIATION...19/2351Z.

At 2330Z, there was no marine layer at KLAX. 

Moderate to high confidence in the current forecast. There is a 
moderate (50 percent) chance of MVFR conditions at KSMO, KLAX and 
KLGB late tonight into Wed morning. Otherwise, VFR conditions are 
expected at the airfields thru Wed afternoon.

KLAX...There is a 50 percent chance of MVFR conditions from about
11Z-17Z. Otherwise, VFR conditions are expected thru the TAF
period.

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

&&

.MARINE...19/113 PM.

Small Craft Advisory (SCA) level conditions have expired for the 
southern two outer waters zones. Otherwise, winds and seas are 
expected to be below SCA levels through Thursday. There is a 
moderate (30-40 percent) chance of SCA level northwest winds for 
the waters south of Point Conception, including the southern 
California bight Wednesday evening.

Winds are expected to increase and a large northwest swell is 
expected to build from Friday through the weekend. There is a
moderate (30-40 percent) chance in SCA level winds and hazardous 
seas greater than 10 feet across the coastal waters, especially 
Saturday through Monday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

A storm system will affect the region Sunday and Monday, with 
around two inches of rain in the north of the area, with around
one inch of rain in the south.

&&

$$

PUBLIC...Rorke/jld
AVIATION...Sirard
MARINE...Sweet/Lund
SYNOPSIS...jld

weather.gov/losangeles