Scientific Forecaster Discussion
fxus66 klox 112328
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
328 PM PST Mon Nov 11 2019
Coastal clouds will continue to clear into the afternoon, and
temperatures will be a few degrees above normal. 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-thu)...11/147 PM.
Main impacts the next few days will be localized northeast winds
in the foothills and mountains on Tuesday along with warmer
temperatures district-wide. Then return to onshore flow and more
cloud cover by midweek.
Stratus was stubborn to leave the central coast today, but it did
retreat from the South Coast. Locally gusty northeast winds of
20-30 mph have been persistent across the foothills and mountains
of the San Gabriel Mountains (la co.) And the Santa Lucia
mountains (slo co.) Today. Offshore pressure gradient between lax-
dag is progged to range from -2 to -3.4 mb by Tuesday morning, a
slight increase over today. This will lead to a 5 mph boost in
wind gusts at 25-35 mph for similar areas and push warmer air into
all areas below the mountains for Tuesday afternoon. Still expect
a marine layer up to 1500 feet deep to bring a return of low
clouds and fog to coastal and nearby valley areas later tonight
and early Tuesday. The offshore flow will push the clouds off the
coast earlier than today, but we don't anticipate northeast winds
all the way down to the ocean. There will continue to be brief
critical fire weather conditions where northeast winds occur in
combination with humidities only 8-15 percent across the mountains
and interior valleys.
High pressure ridge overhead on Tuesday will begin to shift
eastward and weaken on Wednesday. Temperatures will begin to
trend downward due to weakening offshore flow and reversal to
onshore flow across most areas by the afternoon. Really do not see
much reason to eliminate morning low clouds and fog along the
coastal areas for Wednesday. Also, model data continues to suggest
more cloud cover for interior sections as flow aloft becomes more
southwesterly late Wednesday and Thursday.
Thursday will be one of the coolest days of the week as a weak
upper level trough passes through southwest California then. High
temperatures will run a solid 5-15 degrees cooler than Tuesday.
There should be plenty of clouds, especially nearer to the coasts
along with breezy southwest winds at times due to a 4 mb onshore
Long term (fri-mon)...11/138 PM.
A weak trough will be shifting through southwest California on
Friday with a trend toward more sunshine and higher pressure. A
ridge will continue to build across the West Coast Saturday and
Sunday. Temperatures will remain on the cool side with onshore
flow for Friday, then a warming trend kicks in by next weekend
with offshore pressure gradients getting stronger. The ecm
ensembles have been consistent for several days now showing the
potential for a moderate Santa Ana wind event next Sunday. At this
point it doesn't look to be a long-lived event and there may be
slight humidity recovery during the middle of the week to delay
fuel dryness when this wind event arrives. However, elevated to
critical fire weather conditions will be possible. For now, Sunday
looks to be the warmest day of the extended forecast with some
cooling by Monday if/when the offshore flow subsides.
Beyond the regular forecast period is a glimmer of hope for
precipitation by the middle of the following week (11/20). The 12z
ecm deterministic is likely overdone on a cut-off low pressure
system, but the ensembles are supporting a potential of moisture.
At this range though, confidence remains very low and there
remains even chances this system would shift to an inside- slider
and another Santa Ana event.
At 2230z at klax, the marine layer was around 1400 feet deep. The
top of the inversion was at 1800 feet with a temperature of 24 c.
Expect widespread stratus to push into coastal areas this evening,
then into the valleys late tonight. Conditions are expected to be
mostly LIFR, except vlifr on the central coast and in some valley
locations, and IFR across coastal sections of l.A. County and
possibly vtu County. Skies are expected to clear by mid morning in
the valleys and by late morning across the coastal plain.
Klax...moderate confidence in the 00z taf. There is a 20-30%
chance that cigs will not arrive until as late as 08z or 09z.
Good confidence that any east wind component will be 5 kt or
Kbur...moderate confidence in the 00z taf. There is a 30% chance
that skies will remain clear and conds will remain VFR thru the pd.
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...11/326 PM.
The marine layer has deepened today, with humidity recovery across
coastal and some coastal valley locations. Meanwhile, offshore winds
gusting between 20 and 30 mph earlier today helped maintain warm and
dry conditions across interior portions of Los Angeles and
Ventura counties. 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. During this time, 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 through Tuesday. Onshore flow is expected to bring some
cooling with humidity recovery late Wednesday through Friday.
There is the potential for a weak to moderate Santa Ana wind event
Hazard potential outlook (thu-mon).
There is the potential for moderate Santa Ana winds next Sunday
with elevated to critical fire weather conditions possible.