FXUS66 KLOX 282117

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
217 PM PDT Mon Sep 28 2020

.SYNOPSIS...28/120 PM.

Dangerous hot and dry conditions are expected much of this week.
Offshore flow will help to drive temperatures up, with triple
digits in the valleys and nineties across some coastal areas
Tuesday through at least Thursday. Temperatures will begin to cool
by Friday and be close to normal by Sunday.


.SHORT TERM (TDY-THU)...28/158 PM.

Synoptically, there is a very large upper level high covering the
entire west coast with 594 DaM heights centered roughly over the
CA-OR border. As the orientation of the ridge shifts tomorrow, the
gusty mountain winds will lessen. Then, as the ridge essentially remains
stationary through Friday the area will heat up under high
heights, sunny skies, and weak offshore flow keeping the cooler
marine air over the water. By this coming weekend the ridge
weakens to about 589 DaM and there zonal flow across Oregon and
Washington. A tropical system, currently disturbance 1 in the
eastern Pacific, has a 70% chance of developing into a cyclone in
the next 48 hours and moving to the northwest - possibly bringing
some clouds to our area in the extended period.

Winds are blowing along the I-5 corridor in the LA Mountains,
with observations showing gusts up to about 40 mph at sites above
4,000 ft. Currently have several stations in Red Flag conditions
with low relative humidity and high wind.  Expecting winds to
strengthen a bit more and become more widespread into the
afternoon - possibly making a push larger into Ventura County.
The low clouds only cleared in the Santa Maria area around 11 am
and are hugging the coastline from Santa Barbara west to the Point
and all the way north up the central coast. Adjusted the max
temperature forecast down a few degrees in Santa Maria area
accordingly. There could be dense fog for a few hours in the

Low end wind advisories are in effect for the L.A. and Ventura
County Mtns as well as the Santa Clarita Valley through mid
afternoon. Santa Ana winds are not expected to be a factor across
much of the Santa Monica Mountains.

Already seeing some temperatures in the valleys to around 100
degrees. The gusty Santa Ana winds, low humidities, and very warm
temperatures will bring elevated to brief critical fire weather
conditions for all areas away from the coast, with critical Red
Flag Warning conditions expected in the LA/Ventura county
mountains and Santa Clarita Valley through this afternoon.

The ridge will persist across much of the west well into western
Canada through much of the week. There will continue to be
relatively week offshore flow through Wednesday, turning off the
natural air conditioner that is the sea breeze. Afternoon high
temperatures will soar with widespread triple digit temperatures
both Tue/Wed with inland coastal areas in the 90s to around 100
for the L.A. County Coast. Wednesday will be the hottest day of
the week with several daily records possibly falling. Heat
products are in effect from Tuesday morning through Thursday

Tuesday night to Wednesday could bring an increase in offshore
flow along the Central Coast resulting in a boost in temps.

No significant changes from Wednesday into Thursday. The ridge
will weaken slightly and temperatures may fall a degree or so, but
it will still be hot.

.LONG TERM (FRI-MON)...28/209 PM.

The upper level ridge across the west will persist through
Saturday, then begin to weaken over much of California through
Monday. There will be some cooling on Friday, with the best
cooling across coastal areas where the sea breeze will make a
return. More widespread cooling is expected by the weekend with
high temperatures getting back to near normal by Sunday.

There is a large spread maximum temperatures in the ensembles for
the extended period (beyond Sunday) indicating a good deal of
uncertainty. It is possibly due to the relative nearness of the
developing tropical system



At 18Z at KLAX, the marine layer was around 1000 ft deep. The top
of the inversion was around 3200 ft with a temp of 28 degrees C.

Low confidence in coastal TAF sites tonight but high confidence
elsewhere. Light offshore flow may not be strong enough to keep
low ceilings and fog from pushing onshore, especially north of Pt

KLAX...Moderate confidence in the 18Z TAF. There is a 20% chance
that IFR or LIFR cigs could return tonight.

KBUR...High confidence in the 18Z TAF with VFR conds expected
through the pd.


.MARINE...28/902 AM.

Across the outer waters...winds and seas are expected to remain
below Small Craft Advisory (SCA) levels through Wed morning. SCA
level NW winds are likely Wed afternoon into Wed night, then
again on Fri. There is a 40% chance of SCA level NW winds Thu and
Thu night.

Across the inner waters north of Pt. Sat, there is a 40% chance of
SCA level NW winds during the afternoon and evening hours Wed and
Fri. Otherwise, conditions are expected to remain below SCA levels
through Fri.

Across the inner waters south of Pt. Conception, there is a 40%
chance of winds reaching SCA levels across the western portion
of the Santa Barbara Channel Fri afternoon. Otherwise, conditions
are expected to remain below SCA levels through Fri.


.FIRE WEATHER...28/411 AM.

Surface high pressure building over the Great Basin will bring
weak Santa Ana winds to the area this morning. Northeasterly wind
gusts between 30 and 45 MPH will develop across the mountains of
Ventura and Los Angeles counties this morning. At the same time,
poor humidity recovery tonight will lead to very low humidity
values (7-15%)later today. With high temperatures rising into the
90s, critical fire weather conditions are expected in these areas
this morning through this afternoon. Therefore, the FIRE WEATHER
WATCHES have been upgraded to RED FLAG WARNINGS valid this morning
through this afternoon.

Elsewhere across the area, elevated fire weather conditions are
expected today due to the hot and dry condition as well as weak
offshore winds. A lingering marine layer influence will moderate
conditions along the coastal plain.

For Tuesday through Friday, weak offshore flow is expected during the
night and morning hours with weak onshore flow in the afternoon and
evening hours. Very hot and dry conditions will persist through the
period. Relative humidity away from the coast will drop into the
teens and single digits with limited overnight recovery. So,
elevated fire weather conditions will continue across all areas.
Additionally, the hot and dry conditions will be favorable for
plume dominated fire behavior on existing and new fires.


CA...Heat Advisory in effect from 10 AM Tuesday to 8 PM PDT
      Thursday for zones 40-41-44>46-88-547. (See LAXNPWLOX).
     Wind Advisory in effect until 3 PM PDT this afternoon for
      zones 53-54-88. (See LAXNPWLOX).
     Red Flag Warning in effect until 5 PM PDT this afternoon for
      zones 253-254-288. (See LAXRFWLOX).



Hot temperatures expected through at least Thursday with near
critical fire weather conditions.





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