Area Forecast Discussion
Issued by NWS Los Angeles, CA
FXUS66 KLOX 250003
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
503 PM PDT SAT SEP 24 2016
Updated aviation and fire discussions
Gusty Santa Ana winds and hot and dry temperatures will peak
Sunday and Monday. A weak low pressure aloft and onshore flow is
expected to bring a cooling trend Tuesday through the end of the
Guidance initialized the surface ridge over the great basin and
thermal trough near shore reasonably well this morning. Relatively
light offshore winds this morning with a lax-dag pressure
difference around 3 mb with light upper level support have
shifted onshore except over the High Country and interior SLO
County early this afternoon. Guidance was consistent with previous
runs and the Santa Ana wind event will strengthen tonight through
Sunday morning. Will continue with wind advisory conditions
beginning in the Los Angeles and Ventura County High Country at
midnight tonight and for the lower elevations 6 AM Sunday. Will
push the end of the event timing back to Monday afternoon as guidance
continues to indicate a similar pressure gradient over the area
Sunday night through Monday morning. Otherwise have adjusted
temperatures up through the period. Expect temperatures will
remain below records but likely be 10-20 degrees above seasonal
normal Sunday and Monday. Guidance differed slightly from previous
runs as a remnant tropical low advances northeast over Baja. The
analog guidance indicated the western limit of high probability of
QPF approximately 0.01 of less over the Los Angeles county
tuesday through Wednesday morning. And have adjusted pops up with
a limit of 14 percent.
Latest guidance was reasonably consistent with previous runs
through the period and dry conditions will persist with a cooling
trend. Temperatures near the coast will likely be 5-10 degrees
below normal within a marine layer while above normal
temperatures persist in the interior under clear skies but the
interior areas are expected to trend cooler by 2-4 degrees each
day through the period. Otherwise the remnant tropical low
centered east of the area will shift east as a mid latitude trough
advances over the Eastern Pacific Wednesday. The mid latitude
trough is expected to amplify while approaching and
height/thickness will lower/decrease over the area through the
At 23Z, there was no marine inversion at KLAX.
High confidence in VFR conditions through Sunday. Northeast winds
with 20+ KT gusts will likely affect KVNY KOXR KWJF KPMD. 40
percent of those winds at KLGB. LLWS likely a concern at times
12-20Z Sunday at KBUR KVNY KOXR, especially at times around
afternoon seabreeze wind shift.
KLAX...High confidence VFR conditions through Sunday. LLWS likely
15-18Z on Sunday due to northeast winds aloft, with a 30 percent
chance of being stronger than +/- 20 KT. There is a 40 percent
chance of east winds at the surface greater than 8 KT.
KBUR...High confidence VFR conditions through Sunday. LLWS likely
13-20Z on Sunday, with a 80 percent chance of being stronger than
+/- 20 KT. There is a 30 percent chance of northeast winds greater
than 20 KT surfacing.
For the Outer Waters, winds will remain below small craft advisory
On the inner waters, there is a 50 percent chance of small craft
advisory level winds Sunday morning from Ventura through Malibu.
There is a 30 percent chance of gusty winds affecting the eastern
shores of Santa Catalina island and Avalon Harbor with steep wind
.FIRE WEATHER...24/500 PM.
An extended period of critical Red Flag fire weather conditions
across much of Los Angeles and Ventura counties through Monday,
with elevated fire danger across remaining areas. Widespread minimum
relative humidities so far today have been between 8 and 15
percent away from the coast. North to northeast winds are currently
gusting 20 to 35 mph across the Los Angeles and Ventura County
Mountains and Valleys with similar winds expected through this
evening. The Santa Ana winds are then expected to increase in
areal coverage and intensity late tonight and especially Sunday,
when the offshore winds are expected to spread all the way to the
coast from Ventura to Malibu with peak gusts ranging up to 55 mph
across the mountains and up to 45 mph closer to the coast. LAX-
Daggett gradient expected to peak around -5 mb on Sunday morning,
along with better upper level wind support. The most critical fire
weather conditions are expected on Sunday across Southern
California due to the stronger Santa Ana winds, widespread triple
digit temperatures, and widespread single digit humidities. This
type of critical fire weather scenario combined with the
exceptionally dry fuels would bring the potential for very rapid
fire spread along with extreme fire behavior (including long range
spotting) for any new fire ignitions. In addition, very warm
temperatures and poor humidities can be expected at night across
the foothills and wind prone areas. Gusty Santa Ana winds will
likely continue Sunday night into Monday but wind gusts are not
expected to be quite as strong and will be more easterly in
nature. Continued very hot and dry conditions on Monday will
likely maintain the critical fire weather conditions.
By Tuesday there is a 10 to 15 percent chance of thunderstorms
across Los Angeles and Ventura counties in response to mid level
moisture possibly working its way into the area from the
southeast. Otherwise, gradual cooling is expected to continue
through the middle to end of next week with a slow increase in
marine layer coverage to the west of the mountains.
CA...Wind Advisory in effect from 6 AM to 6 PM PDT Sunday For
zones 40-41. (See LAXNPWLOX).
Wind Advisory in effect from midnight tonight to 3 PM PDT
Monday For zones 44>46-53-54-547. (See LAXNPWLOX).
Red Flag Warning in effect from midnight tonight to 3 PM PDT
Monday For zones 240-241. (See LAXRFWLOX).
Red Flag Warning in effect until 3 PM PDT Monday For zones
244>246-253-254. (See LAXRFWLOX).