Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/21/21

Area Forecast Discussion

National Weather Service Louisville KY

 920 PM EST Sat Nov 20 2021

.Forecast Update...
Issued at 919 PM EST Sat Nov 20 2021

A warm advection band of light rain is lifting northeast through
southwestern Indiana, but much of this is not hitting the ground
and/or not measurable in the LMK CWA. 0105z SDF AMDAR sounding shows
a massive layer of dry air persisting below 800 mb. Low-level
forcing also remains weak, but the southwesterly LLJ will steadily
increase off to the southwest overnight. Southern Indiana and KY
counties along the river will see much greater rainfall coverage and
accumulations from about 3 AM EST through the mid-morning hours.

&&

.Short Term...(This evening through Sunday)
Issued at 230 PM EST Sat Nov 20 2021

Not a bad November Saturday across the Ohio Valley, with seasonable
temperatures and a decent amount of sunshine filtered by mid/high
clouds in the return flow. Plenty of low-level dry air in place,
which will keep us dry well into tonight.

Upper-level shortwave trof over the Intermountain West will kick
into the Plains by Sunday morning, with low-level jetting and
isentropic lift touching off some light rain by daybreak over
southern Illinois and Indiana. Will keep the evening dry but ramp
POPs up to likely after midnight in southern Indiana with lesser
chances over Kentucky cutting off sharply south of the Western
Kentucky and Bluegrass Parkways.

Low pressure intensifying between Lake Superior and James Bay will
push a cold front toward the Ohio Valley on Sunday, with a well
focused moisture feed along the front. PWAT values just north of 1
inch, but it`s a progressive enough front and instability is weak to
nonexistent. Rainfall amounts will run around a half inch, perhaps
touching 3/4 of an inch over toward Lake Cumberland. Lapse rates
overall don`t support thunder, with only a small sliver of elevated
instability developing over south-central Kentucky. Can`t completely
rule it out but probabilities are too low to mention.

.Long Term...(Sunday night through Saturday)
Issued at 225 PM EST Sat Nov 20 2021

Sunday Night - Wednesday...

Rain will be tapering off from west to east Sunday evening as the
surface cold front exits off to the east. Under steady northwesterly
flow, cooler air will advect into the region with low temperatures
dipping into the upper 20s to lower 30s Monday morning. In the wake
of Sunday`s system, deep upper troughing will remain over the
eastern CONUS into Tuesday before broad ridging aloft progresses
eastward over the area Wednesday. At the surface, high pressure
initially located over the mid MS Valley will gradually drift
towards the region, eventually moving off to the east Wednesday.
Tuesday morning looks to be the coldest of the period as surface
high pressure sits directly overhead, with lows dropping into the
lower 20s and perhaps even into the upper teens. Temperatures will
then gradually moderate towards normals as southerly flow takes hold
on the back side of the high Wednesday, with afternoon temps warming
into the lower to mid 50s.

Thursday - Saturday...

Pattern begins to change heading into Thursday as large upper trough
pushes across the north-central CONUS, with a mid-level low
potentially closing off over the southern Ontario/Upper Great Lakes
region by Thursday night. At the surface, an area of low pressure
will lift NE out of the Upper Midwest through central Ontario,
sending another cold front towards the region. Overall there is
general agreement amongst model guidance that the NE-SW oriented
cold front will begin to push into southern IN by Thursday
morning/early afternoon and continue across the area into the
evening before exiting off to the east Thursday night. However, this
is still a ways out so may continue to see minor shifts in the
timing. Depending on how quickly moisture moves out of the area and
colder air move in, may see some snowflakes mix in on the backside
of the system. High pressure will once again push in behind the
front resulting in mostly dry weather for Friday and Saturday. High
temperatures will generally be in the 40s to lower 50s to end the
week with lows in the mid 20s to lower 30s.

&&

.Aviation...(00Z TAF Issuance)
Issued at 650 PM EST Sat Nov 20 2021

IMPACTS:
- VFR with increasing mid-level clouds tonight
- Rain showers arrive around daybreak at SDF and HNB, early
  afternoon for BWG and LEX
- Lower cig/vis Sunday afternoon with IFR likely

DISCUSSION:

SCT-BKN mid-level ceilings are forecast to thicken and gradually
lower through the early morning hours of Sunday. HNB/SDF will see
light rain showers move in 07-10z as the low-level jet increases
from the southwest. Then from late morning through the afternoon, a
band of showers will march east across the region accompanied by a
significant lowering of ceilings. Expect lower vis to accompany the
rain showers and low ceilings as well. S-SE winds will veer SW
Sunday afternoon and W Sunday evening.

CONFIDENCE:

Medium-high on all elements.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...EBW
Short Term...RAS
Long Term...JML
Aviation...EBW



Area Forecast Discussion

National Weather Service Los Angeles/Oxnard CA

 612 AM PST Sat Nov 20 2021

.SYNOPSIS...20/327 AM.

An offshore flow pattern in place across the area will bring a
warming and drying trend through Monday. Gusty offshore winds are
likely for portions of the area through the weekend and into
early Monday. Cooler conditions are forecast for Tuesday and
Wednesday as a weak weather system moves over the region. A few
showers are possible, but mainly a cooling trend is expected. An
another Santa Ana wind event is possible between Thanksgiving
Day and Saturday.

&&

.SHORT TERM (TDY-MON)...20/451 AM.

The latest water vapor imagery shows what`s left of a frontal
boundary pushing south through Monterey County early this morning.
This mainly dry front will push south while continuing to wash
out. Ahead of the boundary, a well-entrenched marine layer stratus
pattern is in place. KLAX AMDAR soundings indicate a 1500 foot
deep marine layer depth currently, which agrees well with NAM BUFR
time height sections. As BUFR time height section suggest and
surface observations verify, it is likely shallower along the
Central Coast. Dense fog has developed across most coastal and
valley areas north of Point Conception and a dense fog advisory
was added through 9 am this morning. A dense fog advisory was also
added for the San Fernando and San Gabriel Valleys as low clouds
and fog have also turned dense in these areas similar to last
night.

Farther upstream, infrared satellite imagery and nighttime
microphysics RGBs show offshore flow starting to establish over
the San Francisco Bay area. Offshore flow will establish across
portion of the region later today making for a tricky temperature
forecast for the coast and lower valleys. These areas could remain
mired in the depth of the marine layer and keep the air mass on
the cooler side today. The forecast goes warmer than forecast
guidance for the valleys, foothills, and mountains but remains
near to slightly cooler than forecast guidance for the coastal
locales. Northeast low-level flow developing later this morning
will likely drive weather pattern through the weekend. Gusty
Santa Lucia winds will develop later this morning as the offshore
push establishes up north then takes a firmer hold across Los
Angeles and Ventura Counties tonight. Wind advisories were added
for gusty Santa Lucia winds from late this morning through Sunday
morning, and for gusty Santa Ana winds from late tonight through
Monday afternoon.

There is some concern that winds could reach damaging levels in
some spots late tonight and into Sunday morning. Deterministic 00Z
NAM-WRF solutions put 950 mb and 850 mb winds on the upper-
threshold for high wind warning levels, but 06Z solutions have
backed off. EPS ensemble members also indicate a similar stance
for K3A6 keeping gusts between 45 and 55 mph. A few perturbations
do increase winds above 55 mph to around 60 mph. Confidence is
highest with a high-end advisory moderate Santa Ana wind event,
but this will need to be monitored by future shifts for
strengthening.

Temperatures remain on the warm side of forecast guidance for
Sunday and Monday and toward the higher end of EPS ensemble
members for the Southland, including KBUR, KCMA, KCQT, KLAX, and
KLGB. Temperature across most of the coastal and valley locations
will likely range between the upper 70s and upper 80s on Sunday.
Some cooling is possible on Monday, but it will depend much upon
how quick the flow pattern transition from offshore to onshore.
Ensemble members lean cooler in the EPS for most sites, local
knowledge might trump the coarseness of the ensemble model
resolution. Local knowledge suggest that transition days can be
tricky and it is best to take a warmer stance south of Point
Conception.

.LONG TERM (TUE-FRI)...20/450 AM.

A upper-level trough near 30N and 135W this morning will likely
phase with a shortwave dropping down the state this evening and
consolidate offshore to the southwest of Los Angeles over the
weekend. This trough will then lift northeast into the region.
Local knowledge suggests that the forecast models struggle with
troughing to the southwest of the region and the forecast should
lean wetter. Deterministic models hint at a sizable cloud mass
moving northeast with it, but ensemble members are struggling pick
up on it in the QPF values. A few members of CMC ensembles do
bring measurable rain to the KEMT, KPOC, and KAVX. PoPs were
nudged higher for Monday night and into Tuesday across Los Angeles
County as the trough lifts out, then a quick hitter shortwave
drops in behind it between Tuesday night and Wednesday. A cooler
air mass will spread in behind the shortwave for Wednesday and
temperatures forecast break away from NBM values for this period.
Future shifts will need monitor this portion of the forecast
period for any changes as this portion of the forecast could
become impactful.

Almost all ensemble members of the EPS and GEFS indicate
offshore flow developing between Thanksgiving Day and the end of
the week. Deterministic solutions give credence to a possibly
stronger event than previously surmised as decent northeast winds
develop at the middle levels of the atmosphere. With still much
variation in the across the CMC, GEFS, and EPS ensemble,
confidence sits highest in offshore flow developing and a warming
and drying trend establishing, but less confidence exists in the
timing and strength of the event.

&&

.AVIATION...20/1411Z.

At 1230Z at KLAX, the marine layer was 1600 feet deep. The top of
the inversion was around 3200 feet with a temperature of 15C.

Widespread low clouds in all coastal and most valley areas.
Conds were mostly LIFR to VLIFR, except IFR to low MVFR across
coastal sections of L.A. and VTU Counties. Expect skies to clear
by mid to late morning in the valleys, and by noon near the coast.
There is a chance that clouds could linger once again at some
beaches into the afternoon. Low clouds may return to some coastal
areas this evening, with generally IFR to LIFR conds, but will
likely clear overnight as flow turns offshore. Gusty NE winds will
begin to affect the mtns and valleys of L.A. and VTU Counties by
late evening with mdt to stg UDDF and some LLWS.

KLAX...Moderate confidence in the 12Z TAF. There is a 20-30%
chance that cigs will slip into the IFR category thru 16Z. There
is a 20% chance that cigs will could linger through 21Z. There is
a 20% chance that skies will remain clear tonight.

KBUR...Moderate confidence in the 12Z TAF. There is a 20% chance
that cigs will scatter out as early as 16Z. There is 20% chance
that there will be a period of IFR cigs between 06Z and 10Z
tonight.

&&

.MARINE...20/527 AM.

For the outer waters, fairly high confidence in the forecast.
Winds are expected to drop below Small Craft Advisory (SCA)
levels later this morning. There is a 30% chance that SCA level
winds will continue into this evening. There is a 30% chance of
SCA level NE winds across portions south of San Miguel Island and
north of San Nicolas Island on Sun. Otherwise, SCA conds are not
expected Sun thru Mon. SCA level NW winds are likely Tue thru Wed.

For the Inner Waters north of Pt. Sal, moderate confidence in the
forecast. There is a 20-30% chance of SCA level NE winds near
shore late tonight Sun morning. SCA level NW winds are expected
Tue, then there is a 40% chance of SCA level NW winds Wed.

For the Inner Waters south of Pt. Conception, moderate to high
confidence in the forecast. Late tonight and Sun, and again late
Sun night/Mon morning, SCA level NE winds are likely from the
eastern Santa Barbara Channel south to Santa Monica. There is a
20-30% chance of SCA level NE winds affecting Avalon Harbor. There
is a 40% chance of SCA level W-NW winds across western SBA
Channel Tue afternoon and evening. Otherwise, winds and seas will
remain below SCA levels Mon afternoon thru Wed.

&&

.FIRE WEATHER...20/455 AM.

A Red Flag Warning remains in effect for the Sunday/Monday time
period due to increased confidence of Red Flag conditions in these
areas. A Fire Weather Watch remains in effect for Sunday across
the mountains of Santa Barbara and San Luis Obispo counties due to
less certainty in these areas reaching Red Flag thresholds.
Northeast to east Santa Ana winds are still on track to increase
late Saturday Night into Sunday, with the peak winds expected
Sunday morning and afternoon. During this peak, offshore wind
gusts of 35 to 55 mph are expected across Los Angeles and Ventura
Counties, except isolated gusts up to 60 mph in favored mountains
and foothills. In addition, wind gusts of 30 to 40 mph could
extend into the mountains of Santa Barbara and San Luis Obispo
counties on Sunday. Gusty Santa Ana winds are expected to continue
into Monday morning, however wind gust speeds are expected to be
10 to 15 mph less than Sunday. Humidities are expected to fall to
around 15 to 20 percent by mid morning Sunday, potentially
lowering to between 8 and 15 percent by Sunday afternoon and
evening, and again on Monday. Temperatures generally look to peak
between 75 and 85 degrees. The potential for Red Flag conditions
is around 80 percent for Los Angeles and Ventura Counties,
resulting in the upgrade to the Red Flag Warning. The confidence
in Red Flag Warning conditions for the mountains of Santa Barbara
and San Luis Obispo counties remains around 50 percent, resulting
in less certainty in an upgrade to Red Flag Warning for those
areas.

Conditions are expected to improve Monday night into Tuesday. There is
the potential for another round of weak to moderate offshore winds and
dry conditions Wednesday through Friday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory in effect until 9 AM PST this morning for
      zones 34>37-46-547. (See LAXNPWLOX).
     Wind Advisory in effect until 8 AM PST Sunday for zone 34. (See LAXNPWLOX).
     Wind Advisory in effect from 3 AM Sunday to noon PST Monday
      for zones 40-41. (See LAXNPWLOX).
     Wind Advisory in effect from 9 PM this evening to 3 PM PST
      Monday for zones 44>46-53-54-88-547. (See LAXNPWLOX).
     Red Flag Warning in effect from 9 AM Sunday to 3 PM PST
      Monday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
     Fire Weather Watch in effect from Sunday morning through
      Sunday evening for zones 251-252. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 AM Sunday to noon PST
      Monday for zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PST this morning
      for zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (MON-FRI).

Critical fire weather conditions and gusty Santa Ana
winds are likely into Monday. Another Santa Ana wind event is
possible for the latter half of week.

&&

$$

PUBLIC...Hall
AVIATION...DB
MARINE...DB
FIRE...Hall/Gomberg
SYNOPSIS...Hall

weather.gov/losangeles