Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 240619
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1119 PM PDT SAT JUL 23 2016
...Aviation discussion updated...
Weakening high pressure and an increase in onshore flow will
result in a significant cool down tomorrow, but temperatures will
remain slightly above normal through most of next week. Low clouds
and fog will return to parts of the coastal plain starting
tomorrow as well. Monsoonal moisture may bring a slight chance of
mountain and desert thunderstorms by late next week.
As expected, some modest cooling occurred across the Los Angeles
and Ventura County Valleys today due to a weaker northerly
gradient compared to Friday. Also, a weak eddy spun up to our
south driving in some patchy stratus with dense fog around
Redondo Beach and the South Bay this morning and early afternoon
hours. Because of this Long Beach actually cooled 10 degrees to 88
degrees today from Friday`s 98. However Downtown Los Angeles
actually warmed a couple degrees to reach 97 degrees and tie the
record for this day back in 2006. Also Palmdale tied it`s record
for today recording 108 degrees. High Temps were up 3 to 6
degrees across the Antelope Valley as expected. Mainly due to
weaker northerly surface gradients that helped scorch the valleys
It was another very hot day across inland areas as widespread
triple digit temps continued across most valleys. The Sandfire
wildfire continued to show explosive fire behavior once again today.
The upper steering winds brought plenty of smoke across the L.A.
county valleys as well as the eastern Ventura County valleys
earlier this morning into this afternoon. The wind currents above
8000 ft were out of the NE and continued to blow smoke all the way
down towards Santa Catalina Island today through this evening.
Synoptically the strong upper ridge that has affected much of the
southern half of the U.S will begin to weaken across the west
coast with a weak trough developing aloft across much of
California beginning tomorrow. With heights continuing to be
around 594 DM it will remain quite hot across inland areas.
However tonight, models are showing a Catalina Eddy developing
across the SoCal bight. Although latest satellite imagery remained
mostly clear except for the smoke layer over LA county and
adjacent coastal waters, low clouds should begin to develop due to
the cyclonic flow of the eddy. The latest AMDAR sounding near LAX
indicated the marine layer depth around 700 ft with a strong
inversion in place. This should translate into low clouds
developing overnight with the possibility of patchy dense fog
along coastal areas of LA and VTU counties. Some low clouds could
reach the SBA south coast around Sun- up Sunday morning but
confidence is low overall with the timing of the stratus and how
widespread it will get S of Point Conception. For the Central
Coast, there should be some patchy low clouds and dense fog right
along the coast and should reach Santa Maria but might not reach
SLO. Again, low confidence with the areal coverage of stratus.
Some fog could be dense.
For Sunday expecting widespread cooling across the entire region
with the exception of the Cuyama Valley which should be up a few
degrees from today`s 91. Most valleys will experience highs in
the 90s with a couple locations possibly reaching 100 degrees
including Woodland Hills. Meanwhile, the Antelope Valley
will continue to see triple digit heat. Best cooling should be
across the inland coastal areas by about 10 degrees with most
coastal areas ranging from the 70s to mid 80s inland. Expect a
stronger onshore gradient between LAX- DAG which should help push
the smoke away from the valleys and aimed more into the Antelope
Valley by the afternoon hours.
***from previous discussion***
A relatively shallow marine inversion will continue for Monday and
Tuesday with the possibility of dense fog with limited
visibilities still. Varying amounts of night and morning low
clouds and fog are expected to affect much of the coastal plain
and some of the adjacent vlys later tonight thru Tue morning.
Otherwise, mostly clear skies will prevail during the period,
except for some afternoon cu buildups over the mtns and Antelope
vly Tue afternoon. Stronger onshore flow can be expected each
afternoon thru Tue as well, with gusty s to w winds expected over
the foothills, mtns and deserts. The re- organization of the
marine layer and stronger onshore flow will result in cooler
temperatures. Even so, highs will still be several degrees above
normal each day with the warmest vlys and foothills reaching the
90s to around 100, except 102 to 106 in the Antelope Vly.
EC/GFS in generally good agreement during the medium range. An upper
high will build over NV into UT by Wed and remain centered over this
area for the most part thru Sat. The position of the upper high will
open the door for some monsoonal moisture to start to creep into srn
CA during the period, but most of the moisture should remain e of
the forecast area thru Thu. The GFS was indicating a bit deeper
moisture intrusion from the e on Fri and Sat, with PWAT values
around 1.15 to 1.25 inches moving inland over VTU/L.A.Counties. A
slight chance of afternoon and early evening showers and
thunderstorms can be expected for the L.A./VTU mtns and Antelope Vly
for Fri and Sat, altho there could be an isolated thunderstorm as
early as Wed or Thu afternoon, but chances of that occurring is less
than 15 percent. Otherwise, some afternoon cu buildups can be
expected over the mtns and deserts each day Wed thru Sat. Marine
layer clouds will continue to affect the cst and some adjacent vlys
night and morning hours thru the period as well. Temps are forecast
to change little Wed thru Fri, then cool slightly for Sat, but highs
will remain several degrees above normal for most areas. The warmest
vlys and foothills Wed thru Fri should reach the 90s to 104, except
the Antelope Vly will be in the 102 to 107 deg range each day.
At 04Z at KLAX, the inversion was around 3300 feet deep. The top
of the inversion was near 3500 feet with a temperature of 28
Overall... Low to moderate confidence in the 06z TAFs. The reduced
confidence is primarily due to the uncertainty in the timing...
location... and intensity of the marine intrusion. An eddy is
expected to develop in the bight that would result in a marine
intrusion overnight in the coastal areas south of Point
Conception. Stratus that develops in this area would likely result
in LIFR/IFR conditions. Patchy dense fog will develop along the
coast north of Point Conception and is expected to affect KSMX but
not KSBP. Fog that develops in this area would likely result in
LIFR/IFR conditions. Low clouds and fog will diminish by 18z.
Smoke will be in the 100-120 height range through much of Los
Angeles and Ventura Counties. Otherwise and elsewhere VFR
conditions will prevail.
KLAX... Moderate confidence in the 06z TAF. The reduced
confidence is primarily due to the uncertainty in the timing and intensity
of the marine intrusion. An eddy is expected to develop in the
bight that would result in a marine intrusion overnight and resulting
in LIFR/IFR conditions. Low CIGS will diminish by 17z. Smoke will
be in the 100-120 height range through much of the period. Otherwise
VFR conditions will prevail.
KBUR... Moderate confidence in the 06z TAF. The reduced
confidence is primarily due to the uncertainty in the timing and intensity
of the marine intrusion. There is a ten percent chance of low CIGs 11z-15z.
Smoke will be in the 100-120 height range through much of the period.
Otherwise VFR conditions will prevail.
Northwest winds will remain at SCA levels over the outer waters
through late tonight. There is a 40% chance that SCA winds will
continue over the northern outer waters through Sunday morning.
Otherwise...winds will diminish some but remain in the 10 to 20
knot range over the outer waters through Monday night. There is a
30% chance of SCA wind gusts during the afternoon and evening
hours over the outer waters Sunday and Monday. Short period seas
are near ten feet. Mainly light winds are expected over the near-
shore waters...except for the waters north of Point Sal where
locally gusty winds will gradually diminish overnight.
Patchy dense fog with visibility 1 nm or less is expected tonight
into Sunday morning.
.FIRE WEATHER... 23/400 PM.
Red flag warning remains in effect for the mountains in Santa
Barbara, Ventura, and Los Angeles Counties, as well as the Santa
Barbara County South Coast in the foothill areas through Midnight
tonight due to gusty winds, extremely low relative humidity, and
hot temperatures. Widespread humidities in single digits and teens
Low level winds around the Sand Fire will continue to be south to
southwest gusting 20 to 25 mph through this evening, and will
be slightly stronger on Sunday afternoon/evening. The upper level
winds are from the north which is currently transporting
considerable smoke and ash into the valleys and coast of Los
Angeles County and eastern Ventura county. As of 4 pm, humidities
around the Sand Fire will continue to range between 10 and 15
percent this afternoon with temperatures near 100 degrees.
Humidities will recover slightly later tonight, generally in the
20 to 30 percent range. With humidities lowering back to between
10 and 20 percent on Sunday, there will be the potential for brief
critical fire weather conditions near the Sand Fire on Sunday
afternoon and evening as the gusty onshore winds increase.
CA...Red Flag Warning in effect until midnight PDT tonight For
zones 239-252-253-259. (See LAXRFWLOX).
Red Flag Warning in effect until 10 PM PDT Sunday For zone
254. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday For
zones 670-673-676. (See LAXMWWLOX).