Scientific Forecaster Discussion
fxus66 klox 150625
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
1125 PM PDT Sat Sep 14 2019
High pressure over the region will begin to shift east tonight
and Sunday as an upper low digs south over the West Coast. Cooler
temperatures are expected tomorrow and through much of next week
as onshore flow prevails. Coastal areas are likely to see night
through morning low clouds and fog through the weekend and into
the coming week.
Short term (sat-tue)...14/811 PM.
After another very warm day across southwest California, a cooling
trend will begin tomorrow as an upper low moves into the Pacific
northwest with a trough extending south along the West Coast.
Significant cooling is expected along the central coast due to the
onset of onshore flow, with highs dropping between 10 to 20
degrees compared to today's highs. Coastal areas south of Point
Conception should also see cooling of around 10 degrees, with
more modest cooling further inland.
For tonight, a shallow marine layer continues with low clouds
expected to fill in along portions of the central coast. Further
south, the forecast is lower confidence as a coastal eddy
struggles to form near the l.A. Coast and the NAM shows weak
offshore flow near Oxnard. However, there is a good chance of
dense fog developing along with any low clouds that form.
Meanwhile, northerly winds along the western Santa Barbara South
Coast should help to keep that area of the coast clear overnight.
***From previous discussion***
The trough will deepen along the West Coast Monday, though
surprisingly models have been reluctant to show much deepening in
the marine layer despite the strong onshore trends and fairly
significant lowering of heights aloft. Either way, another day of
cooling expected Monday with highs dropping to near or even
slightly below normal.
Models still showing the trough picking up some mid and upper
level moisture from the southwest Monday with some elevated
instability. Still can't completely rule out some sprinkles as
this moves through but it's still very dry below 700mb and most
likely all we'll see are some clouds and maybe some virga.
Models in good agreement showing the trough exiting to the east
Monday night with some northwest flow and weakening onshore
gradients Tuesday. This should lead to some temperature recovery
though probably not more than a few degrees over monday's levels.
Will likely see some increase in northerly winds across the
western portion of the forecast area, including southern sb County
which may see some near advisory level winds Monday evening.
Long term (wed-sat)...14/147 PM.
The minor Tuesday recovery in temps will be short-lived as models
have been consistent showing another fairly deep trough diving
south along the West Coast Wednesday into Thursday. Probably
either little change or slightly cooler Wednesday with more
cooling Thursday as the trough bottoms out over California. The
GFS is noticeably deeper with it than the European model (ecmwf) and does drag a
very weak front through the area Thursday afternoon, but none of
the ensemble solutions show the system holding together well
enough to bring any rain so at most just a deepening marine layer,
possibly some morning drizzle, and cooler temps.
The upper low moves into the northern plains Friday but a weak
trough will linger back through California into the weekend which
will temper the warming trend. Models have been advertising
weakening onshore gradients and possibly some very light offshore
flow by next Saturday but low confidence in this. Either way temps
should be bouncing back up to near or slightly above normal levels
by next weekend.
At 0530z at klax, the marine layer was 700 feet deep. The top of
the marine inversion was 1500 feet with a temperature of 30 c.
Low confidence in the coastal tafs (xcp ksba) and high confidence
for all inland sites. LIFR conds should develop at all coastal
sites except ksba which should remain clear. There is a 20 percent
chc that sites koxr and south will stay VFR. Low confidence in
timing...arrival times could be off by +/- 2 hours. Good
confidence that VFR transition should occur within an hour of
fcst. Low confidence in return of stratus after 15/04z.
Klax...low confidence in taf through 17z and then again after 05z.
There is a 20 percent chc of no cig/vis restrictions. If cigs do
arrive they could arrive anytime between 10z and 14z. Good
confidence in VFR transition. Good confidence in no east wind
component greater than 4 kt.
Kbur...high confidence in VFR taf.
Outer waters...Small Craft Advisory issued for pzz670 through late tonight with
gusts to 25 kt over the northwest portion. 40% chance that the Small Craft Advisory
gusts continue through the day on Sunday. Otherwise, winds should
remain below Small Craft Advisory levels through Sunday night, then increase to Small Craft Advisory
throughout the outer waters and continue through Wednesday.
Inner waters north of Point Conception...moderate confidence that
conditions will remain below Small Craft Advisory levels through Monday morning,
followed by a 40% chance of Small Craft Advisory gusts Monday afternoon and
evening, and again on Tuesday.
Inner waters S of Point Conception...winds should remain below
(sca) thresholds through the period, except for a 50% chance of
(sca) west to northwest gusts by Monday evening and Tuesday across the
western portion of the Santa Barbara Channel.
Patchy dense fog is expected to form over portions of the waters
late tonight, including areas off the central coast and along the
Fire weather...14/506 PM.
Temperatures climbed to 100 to 105 degrees today across warmest
Valley, Mountain, and desert areas, while the central coast has
again topped out between 90 and 100 degrees. The hot temperatures
will bring the potential for large vertical plume growth with
fire ignitions through this evening, with peak mixing heights
ranging from 10,000 to 15,000 feet. Minimum humidities between 7
and 15 percent will continue today across the mountains, valleys,
and deserts, with the central coast lowering to between 15 and 25
percent. Poor overnight humidities will bring added fire danger to
the mountains and foothills. Elevated fire weather conditions
continue across the mountains, deserts, valleys, and central coast
today due to the hot and dry conditions along with the dry fuels.
An upper level trough of low pressure will bring strengthening onshore
flow to the region Sunday into Monday with onshore winds gusting
to 25 to 35 mph across interior sections on Sunday, then
increasing to 30 to 40 mph by Monday. On Sunday, temperatures
across inland areas are still expected to be in the 90s, with
further cooling on Monday. Meanwhile, humidities between 8 and 15
percent will be common across interior sections on Sunday. By
Monday, a stronger onshore flow pattern combined with a deepening
marine layer will bring cooling and humidity recovery to coastal
and valley areas, however a pocket of drier air will remain over
the la/Ventura County mountains and deserts where there could
still be humidities between 10 and 20 percent. The gusty onshore
winds combined with lingering dry air will bring elevated to brief
critical fire weather conditions to all interior areas on Sunday,
then mostly confined to the la/Ventura County mountains and
Antelope Valley by Monday.
Pz...Small Craft Advisory in effect until 3 am PDT Sunday for zone
670. (See laxmwwlox).
Hazard potential outlook (tue-sat).
No significant hazards expected.