Scientific Forecaster Discussion
fxus66 klox 182106
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
206 PM PDT sun Aug 18 2019
Temperatures are near normal today but will warm into midweek
then cool again into next weekend. Many locations will have triple
digit temperatures Wednesday and Thursday. Overnight and morning
low clouds and fog will diminish in area a bit each day through
Thursday then expand again beginning Friday.
Short term (tdy-wed)...18/203 PM.
The marine inversion early this afternoon was around 2400 ft deep at
lax. Low clouds have cleared mostly off the coast early this
afternoon, altho some were persisting at a few beaches. Little
change can be expected the rest of the afternoon, with mostly sunny
Good onshore gradients (+7.9 mb lax-dag at 00z according to the
latest nam) will promote gusty S to west winds across much of the
foothills, mtns and deserts this afternoon. This will also help to
keep temps quite a bit below normal across the forecast area, with
highs expected to reach only into the 80s in the warmer vlys and
lower mtns, altho the Antelope Vly should still warm into the 90s
this afternoon. Temps overall across the region today will be 6-15
deg below normal for this time of year.
An upper level trof will persist along and off the California coast thru
today, with 500 mb heights in the 586-588 dm range. A large upper level
high centered over southern Texas today will start to slowly expand
west and into srn California tonight thru Tue, with 500 mb heights expected to
increase to 589-591 dm for Mon afternoon and 591-593 dm for Tue
afternoon. A weakness in the upper ridge will allow a very weak
upper trof (h5 heights 591-593 dm) to move into the region on Wed. A
dry SW flow aloft will prevail thru Tue then weaken on Wed.
The marine inversion is expected to shrink to about 1800-2200 ft or
so tonight into Mon morning, and probably down to 1000-1500 ft for
Mon night into Tue morning and below 1000 ft deep Tue night into Wed
morning. Plenty of night and morning low clouds and fog will affect
the coastal areas into portions of the adjacent vlys tonight and
Mon, then be confined mainly to the central coast, Santa Ynez Vly
and the coastal areas S of Point Conception Mon night into Tue
morning. The low clouds should just be along the central coast and
southern l.A. County coast for Tue night into Wed morning. Low
clouds and fog will also likely affect the Salinas river Vly for the
late night and morning hours tonight thru Tue morning. Otherwise,
mostly clear skies will continue across swrn California thru Wed afternoon.
The onshore flow will slowly decrease, with the lax-dag forecast
gradient (nam) expected to be about +7.5 mb Mon afternoon and +6.5
mb Tue afternoon. Some gusty S-west afternoon and evening winds will
continue for the foothills, mtns and deserts especially thru Mon
afternoon. Some gusty northwest winds are also forecast for the central
coast during the period.
It looks like the sba-smx gradient will decrease quite a bit by Tue
evening (-3.9 mb according to the nam) and this will help to
generate a decent sundowner across the sba County S coast and Santa
Ynez mtns. Gusty northerly winds to advisory levels will be possible
below and thru the passes and canyons mainly west of Goleta Tue
Temps are expected to warm slightly to about 2-7 deg below normal
for Mon. On Tue, temps will continue to warm up, with highs ranging
from slightly below normal along the coast to about 2-8 deg above
normal inland. An even sharper warm-up is forecast for Wed with
temps away from the immediate coast rising to 4-12 deg above normal
overall. The warmest vlys and lower mtns should reach the mid 80s to
lower 90s Mon, and 90s to near 100 on Tue, and upper 90s to 104 on
Wed. The expected hot temps on Wed may eventually prompt the
issuance of heat advisories in the warmest inland locations.
Long term (thu-sun)...18/205 PM.
Very weak upper level troffiness will linger on Thu then upper
level ridging should build back into the area Fri thru sun, with
500 mb heights lingering in the 591-593 dm range overall.
The marine inversion should shrink further on Thu, with low
clouds expected to remain off the coast. The inversion should
increase only slightly for Fri thru sun, and some increased
onshore flow should help the low clouds move back into the central
coast, l.A. County coast and southern San Gabriel Vly each night
and morning. Otherwise, a dry air mass will persist over the area
for mostly clear skies thru the extended period.
Temps will continue to be quite hot and about 4-12 deg above
normal away from the coast on Thu, then be about 2-10 deg above
normal away from the coast for Fri thru sun. Another day of
possible heat advisories for some inland areas can be expected on
At 1615z, the marine inversion at klax was based at 2800 feet.
The top of the inversion was 4600 feet with a temperature
of 21 degrees celsius.
Overall, moderate confidence in 18z coastal/valley tafs and high
confidence in desert tafs. Current MVFR cigs are expected to
dissipate early this afternoon. For tonight, high confidence in
return of MVFR/IFR cigs to all coastal/valley sites, but only
moderate confidence in timing.
Klax...overall, moderate confidence in 18z taf. There is a 40%
chance that current MVFR cigs may not dissipate until 21z. For
tonight, high confidence in return of MVFR cigs, but only moderate
confidence in timing (could be +/- 2 hours of current 03z
Kbur...overall, moderate confidence in 18z taf. High confidence in
return of IFR cigs tonight, but only moderate confidence in timing
(could be +/- 2 hours of current 08z forecast).
For the outer waters, moderate to high confidence in current
forecast. There is a 50% chance of Small Craft Advisory (sca)
level winds Monday afternoon. From Monday night through Thursday,
Small Craft Advisory level winds are likely. On Friday, high confidence in winds
and seas remaining below Small Craft Advisory levels.
For the inner waters north of Point Sal, moderate to high
confidence in current forecast. There is a 40% chance of Small Craft Advisory level
winds Monday afternoon and evening. For Tuesday through Thursday,
there is a 70% chance of Small Craft Advisory level winds each afternoon and
evening. On Friday, high confidence in winds and seas remaining
below Small Craft Advisory levels.
For the inner waters south of Point Conception, moderate to high
confidence in current forecast. And evening. Through Friday, high
confidence in winds and seas remaining below Small Craft Advisory levels for a
majority of the area. The only exception will be the western half
of the Santa Barbara Channel. Across the western half of the Santa
Barbara Channel, there will be a 40% chance of Small Craft Advisory level late
Monday afternoon and evening then a 70% chance of Small Craft Advisory level winds
during the late afternoon and evening hours on Tuesday and
Hazard potential outlook (wed-sun).
Hot temperatures could lead to heat advisories for some inland
areas Wednesday and possibly Thursday. Otherwise, no significant
hazards are expected through the period.