Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 282344
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
444 PM PDT Thu May 28 2020

.SYNOPSIS...28/257 PM.

Afternoon temperatures will be well above normal over inland
regions today. Most coastal locations will be cooler due to areas
of low clouds and fog. Temperatures will begin to cool tomorrow
and will be near normal by Sunday. The Central Coast has a slight
chance of showers Friday night and Saturday.

&&

.SHORT TERM (TDY-SUN)...28/159 PM.

The marine inversion early this afternoon was around 1100 ft deep
deep at LAX. Low clouds persisted at many of the beaches, but
otherwise sunny skies prevailed across the forecast area which
will continue thru the afternoon. Good onshore flow (NAM fcst
LAX-DAG +9.7 mb at 00Z) will bring breezy to gusty onshore winds
to many areas this afternoon, and gusts up to 40 mph are expected
in the L.A. County mtns and Antelope Vly.

Temps will continue to be quite hot away from the coast today with
highs about 6 to 16 deg above normal. The hottest interior vlys and
lower mtns should reach the mid 90s to 101, except up to 103 in the
Antelope Vly. An Excessive Heat Warning continues for the Antelope
Vly thru early this evening, with a Heat Advisory in effect for
the SLO interior vlys. Please see the latest Non-precipitation
Weather Message (LAXNPWLOX) for further details.

A 590 dm H5 upper level ridge will persist over srn CA thru the
afternoon while a 564 dm H5 upper level low will be about 550 NM
SW of Point Conception. The upper level ridge is forecast to push
off to the E tonight and Fri which will allow the upper level low
to move quickly NE to a position about 250 NM WSW of Point
Conception by late Fri. H5 heights over the forecast area are
expected to fall to 578-586 dm by late Fri, with a broad southerly
flow aloft.

The marine inversion should be near 1000 ft or so tonight and Fri
morning. Low clouds and fog are expected along coastal and some vly
areas tonight into Fri, with low clouds likely to be persistent
along coastal areas again thru Fri afternoon. Otherwise, skies
over the region will be mostly clear thru Fri.

The upper level low will continue moving NE Fri night to a position
just west of San Francisco, then push quickly inland over nrn CA
while weakening on Sat. At the surface, a weak frontal system should
move to the Central Coast Fri night into early Sat in response to
the upper level low. H5 heights Fri night will range from 565-573 dm
over SLO/SBA Counties to 575-580 dm further S, then rebound to about
575-581 dm in all areas on Sat as the upper level low moves away.

The marine inversion is forecast to deepen rapidly Fri night into
Sat morning in response to the upper level low and surface front.
More of a deep moist layer should push well into SLO/SBA Counties
with a slight chance to chance of showers expected Fri night into
most of Sat, mainly for SLO County. In addition, the upper level
low should have enough instability associated with it to warrant a
slight chance of thunderstorms Fri night over the coastal waters
well off the central Coast.

Rainfall amounts from this system over SLO/SBA Counties for Fri
night into Sat will be on the light side and generally 0.15 inch
or less, with most of the rain expected in the far nwrn SLO County
foothills.

Further S over VTU/L.A. Counties on Sat, the low clouds should
clear back to or off the coast by afternoon, otherwise skies will
be partly cloudy across the region.

It looks like gusty SW-W winds will prevail Fri afternoon and
evening for many areas thanks to strong onshore gradients (NAM
forecasts LAX-DAG gradients to peak at +10.4 mb). Winds may even
reach Advisory levels in the SLO County interior vlys and
Antelope Vly with gusts up to 45 to 50 mph. Gusty sub-advisory
SW-W winds should persist in many areas on Saturday as well.

For Sat night and Sun, a broad SW flow aloft will prevail over
srn CA as another upper level trof moves into the E Pac. The
marine layer pattern should persist with night and morning low
clouds and fog for the coast and vlys. There will also be plenty
of mid and hi level clouds moving in on Sun for mostly cloudy
skies overall thru the day. Breezy onshore winds will continue
especially during the afternoon and early evening.

Temps are forecast to turn much cooler on Fri to near normal to
slightly above normal, except 5-10 deg above normal in the Antelope
Vly. Highs will be in the 80s to around 90 in the warmest vlys and
lower mtns, and mostly in the 90s for the Antelope Vly. Further
cooling to about 3 to 7 deg below normal is expected for Sat, with
the warmest vlys and lower mtns reaching the mid 70s to low 80s.
Temps should then turn slightly warmer for most areas on Sun, with
the warmest vlys and lower mtns topping out in the upper 70s to
mid 80s, except around 90 in the Antelope Vly.

.LONG TERM (MON-THU)...28/201 PM.

The EC and GFS continue to show some disagreement in the medium
range, especially for Wed and Thu. Overall, a large upper level
trof will persist just off the W coast Mon, then an upper level
low will develop at the base of the upper level trof a few hundred
miles off the SW CA coast on Tue. This upper level low is forecast
by the GFS to track NE and into swrn CA on Wed, then slowly E to
the CA/AZ border by late Thu, while the EC keeps this system
nearly stationary just off the srn CA coast Wed thru Thu.

Decided to go with the NBM which kept dry weather and near normal
to slightly above normal temps over the fcst area thru the
extended period. Also, night and morning low clouds and fog are
expected thru Wed.

However, both the GFS and GFS ensembles indicate a chance of rain
over the area between late Tue and Wed (possibly convective Wed
with the upper low), while the EC and EC ensembles trend mostly
dry except for hints on the EC of afternoon convection over
northern parts of the forecast area on Wed. This continues to be a
low confidence forecast next week with likely forecast changes
from day to day.

&&

.AVIATION...28/2344Z.

At 2305Z at KLAX, the marine layer was around 1400 feet deep. The
top of the inversion was near 3100 feet with a temperature of 22
degrees Celsius.

Moderate to high confidence in the current forecast. Higher
confidence for valley and desert terminals, less confidence for
coastal terminals. Some coastal sections only briefly cleared
before the marine clouds surged back in once again. The marine
clouds will return to remaining coastal and valley sections again
tonight with IFR conditions, gradually giving way to MVFR
conditions south of Point Conception.

KLAX...OVC conditions will continue into Friday morning, with
partial clearing Friday afternoon. There is a 30 percent chance of
marine clouds clearing plus or minus two or more hours from the
forecasted time.
KBUR...VFR conditions will change to IFR with the arrival of
marine clouds this evening, followed by clearing late Friday
morning. There is a 30 percent chance of marine clouds arriving
plus or minus two or more hours from the forecasted time.

&&

.MARINE...28/159 PM.

High confidence that winds and seas will remain below SCA levels
through Friday. There is a 40 percent chance of Small Craft
Advisory strength winds in the outer waters over the weekend.

Areas of dense fog with visibility one nautical mile or less at
times are likely for the coastal waters south through this
morning. Mariners should be prepared to reduce speeds and use GPS
navigation if available.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect until 7 PM PDT this evening for zone
      37. (See LAXNPWLOX).
     Excessive Heat Warning in effect until 7 PM PDT this evening
      for zone 59. (See LAXNPWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

No significant hazards expected.

&&

$$

PUBLIC...Sirard
AVIATION...Sweet
MARINE...Sweet
SYNOPSIS...Kj

weather.gov/losangeles


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