Scientific Forecaster Discussion
fxus66 klox 111904
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
1104 am PST Mon Nov 11 2019
Morning low clouds and fog are expected to clear this afternoon,
and expect low clouds and fog to push inland from the coast
tonight. Temperatures tomorrow will be warmer as some offshore
flow develops, but additional clouds will bring cooler near normal
temperatures for the end of the week.
Short term (tdy-wed)...11/926 am.
Today is the battle of the marine layer versus offshore flow and
so far winds are not strong enough to scour the clouds away.
Marine inversion up to 2000 feet and a fairly weak offshore trend
will result in cool temperatures near the beaches. Most areas are
cooler than yesterday by 4-12 degrees except for where northeast
winds are more prevalent...mainly across mountain zones. Locally
gusty winds of 20-30 mph will be felt in these areas through the
early afternoon. Expect low clouds to retreat to the ocean today,
but not far away from beaches to make a quick reappearance this
evening. Modest changes in the marine layer tonight and a -3.0 mb
lax-dag pressure gradient by morning will shrink the inversion
another 500 feet or so. Evenso there will still be low clouds/fog
across most coastal areas including sections of the la valleys
early Tuesday morning. Northeast winds are likely to be another 5
mph stronger tomorrow in the favored eastern Ventura and western
la mountain and foothill regions. Temperatures will be warmer for
most areas Tuesday.
***From previous discussion***
A ridge will move into the state on Tuesday and hgts will rise to
587 dm. These hgt rises along with the offshore flow will combine
to bring 3 to 6 degrees of warming to the area. These temps are
likely a little lower than would be expected because mid and high
level clouds will be moving into the area from the SW. There is no
upper level or thermal support so there will not be advisory
level winds. Still the warm temps and the 15 to 25 mph winds will
create some fire weather concerns.
Offshore flow weakens Wednesday morning and turns onshore by mid
afternoon. The mid and high clouds will continue to stream in over
the ridge and skies will be mostly cloudy. The clouds and the
reversal of the offshore flow will lead to 4 to 8 degrees of
cooling across the board.
Long term (thu-sun)...11/310 am.
Both the ec and the GFS agree that there will be broad scale
troffing over the West Coast Thursday and Friday with weak (ec) or
moderate (gfs) onshore flow. Weak ridging moves into the area for
the weekend with increasing offshore flow.
The mid and high cloud shield will peak on Thursday. This along
with hgts falling to 578 dm and the increase in onshore flow will
lead to the coolest day of the week. Another 4 to 8 degrees of
cooling will bring most coastal and Vly Max temps into the upper
60s to mid 70s or 1 or 2 degrees blo normal.
The mid and high level clouds will diminish on Friday. The onshore
flow will likely generate some morning stratus along the coast in
the morning. The afternoon will be sunny and this will bring about
several degrees of warming.
The warming trend will continue into the weekend as the ridge will
bring increasing hgts and offshore flow. No real wind concerns
Saturday as the offshore flow is just beginning. Still there will
be 3 to 6 degrees of warming.
Better offshore flow on Sunday but the upper level support is now
forecast to be weaker than it was last night. If the current
forecast is correct there will not be enough upper support for
advisory level winds. Still enough to cause some breezes and
warmer/drier weather which will lead to some fire wx concerns.
Another 3 to 6 degrees of warming will bring Max temps in the 80s
and maybe a few 90s to almost all of the coasts and vlys. These
kinds of temps are 4 to 8 degrees warmer than normal.
At 1701z at klax, the marine layer was around 1800 feet deep. The
top of the inversion was at 3000 feet with a temperature of 21 c.
High confidence in desert and valley tafs. Low to moderate
confidence in remaining tafs. Trended slightly earlier on timing
of the return of cigs tonight. Some coastal taf sites may clear
early Tuesday morning.
Klax...low confidence in taf. The onset of ceilings this evening
is expected to occur a bit earlier. The marine clouds may clear a
few hours earlier Tuesday morning. Good confidence that an east
wind component remains 5 kt or less.
Kbur...high confidence in taf. VFR conditions are expected through
For all of the coastal waters, high confidence that winds and
seas will remain below Small Craft Advisory (sca) level through
Thursday. Confidence lowers on Friday as Small Craft Advisory level winds may make
a return to the offshore waters along the central coast southward
towards San Nicolas Island.
Patchy dense fog with visibility of one nautical mile or less is
likely to impact the coastal waters north of Point Conception
through this morning.
Fire weather...11/919 am.
The marine layer has deepened up this morning, with low clouds
and humidity recovery across coastal and some coastal valley
locations. Meanwhile, offshore winds gusting between 20 and 30 mph
will continue to maintain warm and dry conditions across interior
portions of Los Angeles and Ventura counties today. The offshore
winds are expected to be slightly stronger late tonight into
Tuesday morning, generally gusting between 25 and 35 mph
across interior portions of Los Angeles and Ventura counties.
On Tuesday morning, the lax-Daggett gradient is expected to peak
around -3.5 mb. Minimum humidities are expected to range between
8 and 15 percent across most interior areas today and Tuesday,
with poor humidity recoveries tonight in the foothills and
mountains. The combination of breezy offshore wind conditions,
warm temperatures, and low humidities will bring elevated to brief
critical fire weather conditions to the interior valleys,
mountains, and foothills of Los Angeles and Ventura counties today
through Tuesday. Onshore flow is expected to bring some cooling
with humidity recovery Wednesday through Friday. There is the
potential for a weak to moderate Santa Ana wind event by Sunday.
Hazard potential outlook (wed-sun).
There is the potential for moderate Santa Ana winds next Sunday
with elevated to critical fire weather conditions possible.