Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/11/19
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
903 PM PDT Sat Aug 10 2019
Areas of low clouds and fog will develop over most of the coast
tonight and gusty north winds are expected over southern Santa
Barbara county through late tonight and then again on Sunday
night. Temperatures will be on the rise Sunday through Tuesday as
an upper level trough exits the region and a ridge moves in.
.SHORT TERM (TNT-TUE)...10/902 PM.
The latest satellite imagery shows an upper-level trough over
southeast Oregon, and lifting out into northern Intermountain
region, while an upper-level ridge remains anchored over north
Texas. As the trough`s influence wanes across the area, high
pressure aloft will build in gradually. 500 mb heights slowly
climb each day and a warming and drying trend will likely develop.
The warming is well encapsulated and only a minor tweak will be
made to mountain temperatures for Sunday.
A stubborn and shallow marine layer remains in place this evening.
Stratus is pushing a bit faster into the Central Coast this
evening versus last night. The latest AMDAR soundings from KLAX
indicate a marine layer depth near 700 feet deep this evening.
With a shallow marine layer in place, dense fog could develop
overnight tonight and into Sunday morning, especially along the
Central Coast. Observations are being monitored closely this
evening for the possibility of broader dense fog. Motorists
traveling late tonight and early Saturday morning are advised to
use caution. Slow down, use low beam headlights, and increase the
space around your vehicle and the vehicles around you.
Gusty Sundowner winds continue across southern Santa Barbara
County this evening. KSBA-KSMX surface pressure gradients are a
bit tighter tonight versus last night. A wind advisory remains in
effect and drivers of high-profile vehicles, such as RVs and large
trucks are advised to slow down and use caution. Gusty cross winds
could make controlling your vehicle difficult. Marginal near-
advisory level winds are also possible through Interstate 5
Corridor tonight and into Sunday morning. Local advisory level
gusts could be reached on favored peaks, such as Whitaker Peak
near the Los Angeles-Ventura County line.
An update will be issued shortly.
***From Previous Discussion***
As heights continue to nudge upward Monday into Tuesday, look for
gradual warming and drying trend to continue, especially interior
mountains and valleys, as well as the deserts. As the marine
layer becomes more shallow, looking for night and morning low
clouds and fog to mainly be confined to coastal areas by Monday
.LONG TERM (WED-SAT)...10/214 PM.
Warm temperatures will continue on Wednesday as the upper level
pattern shows little change. Then from Thursday through Sunday
the long range models are showing another upper level trough
deepening across California. This will lead to a cooling trend
Thursday through Saturday, along with increasing onshore winds
in the mountains and deserts.
At 00Z, the marine layer depth was around 750 feet deep at KLAX.
The top of the marine inversion was near 1400 feet with a
temperature near 19 degrees Celsius. There was another inversion
up to around 2500 feet.
Moderate-to-high confidence in the current forecast. Higher
confidence for inland terminals and in flight categories, less
confidence for coastal terminals and in timing. Timing could be up
to +/- 2 hours. LIFR to IFR conditions will likely develop at
Central Coast terminals through at least 15Z. IFR to MVFR
conditions will likely develop at coastal terminals south of Point
Conception, except KSBA. VFR conditions should redevelop between
15Z and 17Z. There is a chance of moderate wind shear and
turbulence at KSBA between through 08Z.
KLAX...There is a 40 percent chance of VFR conditions through the
period. The most likely time period for IFR conditions between 10Z
and 14Z. VFR conditions should redevelop between 15Z and 17Z.
KBUR...VFR conditions are expected throughout the period.
For the Outer Waters, moderate-to-high confidence in the current
forecast. Small Craft Advisory (SCA) winds are expected across
the two northern outer coastal waters (PZZ670-673) through late
Mon night and possibly into Tue. There will also be a 70% chance
for the southern outer waters (PZZ676) to continue with SCA level
winds through late Sunday night. There will then be a 50% chance
of SCA level winds across the outer waters Wed and Thu.
For the Inner Waters north of Point Sal, moderate confidence in
the current forecast. There is a 60%-70% chance of SCA level winds
during the afternoon and evening hours through Mon. After a lull
Tue and Wed, there will be a 40% chance of SCA level winds Thu.
For the Inner Waters south of Point Conception, moderate confidence
in the current forecast. There is a 60% chance that SCA level
winds across the western SBA Channel will continue through
tonight. The strongest gusts will be south of Refugio to Gaviota
with NW to N winds while the rest of the channel will be affected
by westerly winds. There is a 30% chance of SCA level winds for
the western portion of the Santa Barbara Channel on Thu as well.
Otherwise, conditions are forecast to remain below SCA levels.
.FIRE WEATHER...10/326 PM.
The strong upper level trough over the West Coast that brought cooler
temperatures and higher humidities to most areas today will move
north, as an upper level high builds over the area from the east
during the next few days. Onshore winds will continue to range
between 25 and 35 mph across interior sections (with isolated gusts
to 40 mph in the foothills of the Antelope Valley) through this
evening. The lingering dry air over the Antelope Valley and Los
Angeles County mountains will remain through the early evening, with
humidities generally ranging between 15 and 25 percent. The dry
conditions combined with gusty onshore winds will result in elevated
fire weather conditions through this evening across these areas. A
gradual warming and drying trend will occur Sunday through Tuesday
across interior areas, bringing elevated fire weather concerns.
Gusty sundowner winds are expected to be stronger and more widespread
late this afternoon into tonight across the Santa Barbara south
coast and Santa Ynez mountains, strongest across western canyons and
foothills from Gaviota to Goleta where wind gusts between 35 and 45
mph will be common. Isolated gusts up to 55 mph will be possible in
and around Gaviota. Wind gusts of 30 to 40 mph are also possible near
Montecito Hills. Temperatures will warm into the lower to mid 80s in
the foothills and downslope coastal areas through the early evening
hours. The combination of gusty sundowner winds, lowering humidities,
and warm temperatures will result in elevated fire danger across
southern Santa Barbara County late this afternoon into tonight,
especially western portions.
CA...Wind Advisory in effect until 3 AM PDT Sunday for zones
39-52. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
zones 645-650. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Tuesday for
zones 670-673. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Monday for zone
676. (See LAXMWWLOX).
.HAZARD POTENTIAL OUTLOOK (TUE-SAT).
No significant hazards expected.
Area Forecast Discussion
National Weather Service Phoenix AZ
845 PM MST Sat Aug 10 2019
Increasing moisture ahead of a fairly strong disturbance coming
out of northern Mexico today will cause scattered to widespread
showers and thunderstorms through Sunday morning over southern and
eastern Arizona. Heavy rainfall is expected late this afternoon
and evening across southeast Arizona and areas just south and east
of Phoenix. Temperatures will remain slightly below normal for
most areas except southeast California and southwest Arizona where
temperatures will be near normal with drier air preventing any
rainfall chances to the west. Dry air will begin to sweep eastward
late this weekend through most of next week, pushing thunderstorm
chances east into New Mexico as above normal temperatures return.
Impressive and well defined upper disturbance/inverted trof over
southeast and east-central Arizona continued to lift to the
northeast early this evening ahead of a large upper trof moving into
the Pacific Northwest. Latest SPC mesoanalysis page showed that the
primary dynamics/differential vort advection associated with the
feature was across far eastern AZ, mainly east and southeast of
Globe. There was a bit of difluence/divergence aloft at 300mb mainly
over southern Gila County ahead of the advancing inverted trof. 3
hour MLCAPE/surface based CAPE trends show values down substantially
over most of Arizona except a small strip near the New Mexico
border. Earlier southerly outflow winds helped to cool the boundary
layer into the mid 90s and Phoenix is now at 88 degrees. So it now
appears that convection and showers are mostly over for the central
deserts including the greater Phoenix area for the rest of tonight
as subsidence continues to move in behind the exiting disturbance.
We have cancelled the majority of the Flash Flood Watch except for
portions over southern Gila County which may still see some forcing
and scattered showers (maybe a storm) past midnight. Given the high
moisture in place and potential slow storm movement, flooding issues
are not over to our east. Plus, the watch blends seamlessly with our
surrounding office. Forecasts have been tweaked and POPs trimmed
back across much of the area and now agree much better with expected
trends for the rest of tonight.
Scattered to widespread showers and thunderstorms are ongoing
across Pima County and southern Pinal County this afternoon in
association with the inverted trough/MCV still located over
northern Sonora. Additional isolated thunderstorms are developing
along the Mogollon Rim with additional cells in southern Gila
County near Globe. We expect that these cells will continue to
increase in coverage along the fringes of the mid-to-upper level
cloud deck associated with the MCC centered over Tucson whose
deepest convection is continuing to expand on its south and west
side towards the greatest instability.
Although instability should increase a bit along the northern and
western fringes of this MCC, significant mid-to-upper level drying
and a relatively strong midlevel capping inversion over the
Phoenix metro and to the north and east should prevent convection
from holding together as it pushes southwest. Aircraft soundings
from the east and southeast suggest that the midlevel cap is
beginning to erode into a weaker stable layer that may erode more
as deeper moisture moves in from the south. This should allow
cells to increase in coverage over Gila County and potentially
northern Pinal County, with clusters producing locally heavy
rainfall and moist downbursts in this area for the next several
hours. There is more uncertainty for convection developing east of
Gila Bend where mid-to-upper level drying moving in from the
southwest ahead of the longwave trough may preserve the midlevel
stability, but moisture advection from the southeast may increase
instability enough to allow for some locally heavy rainfall. Based
on this, we will maintain the current spatial area of the Flash
Flood Watch through 5 AM MST Sunday, but the western and northern
fringes of which may be cancelled later this evening depending on
how convection evolves over the next several hours.
There is still concern that after a brief lull later this
evening, we may see an uptick in convection later in the overnight
hours as a new MCV or two associated with the stratiform region
of the ongoing MCC forms. Although the broader inverted trough
should continue to move north through eastern Gila County along
the western fringes of the subtropical high centered over Texas,
we cannot rule out the potential for a more localized circulation
to develop further west and track northward. If this occurs,
additional showers and thunderstorms may develop overnight over
northern Pinal, eastern Maricopa, and Gila Counties with storm
motions being very slow (given Corfidi vectors less than 5 knots
possibly favoring backbuilding convection). The greatest potential
for heaviest rainfall tonight appears to be over southern Gila
County where multiscale interactions between any more localized
MCV circulations and the larger-scale inverted trough may occur.
Several model simulations still show 1-2 inch per hour rainfall
totals for southern Gila and northeast Pinal Counties, with very
few showing anything significant further south and west aside from
light to moderate showers which should verify assuming a new MCV
does not develop.
On Sunday morning, the shortwave trough moving to our northeast
will accelerate and weaken as it is picked up by the midlatitude
shortwave moving through the Northern Rockies. The flow aloft
across Arizona will remain out of the west with drying conditions
taking over across the entire state. Sufficient lingering low and
mid level moisture on Sunday will likely cause scattered showers
and thunderstorms across eastern Arizona including Gila County,
but they should be relegated to higher terrain areas only. The
lower deserts will see drier air mixing down to the surface,
especially west of Phoenix allowing high temperatures to warm
closer to 105-107 degrees. Sunday`s highs for the Phoenix area
look to remain slightly below normal, but warmer than previously
thought with highs around 101-103 degrees due to the clearing
skies and drier air aloft. that will eventually translate to
surface drying by Monday.
After tomorrow, next week looks dry and hot as the subtropical
high rebuilds and strengthens to our southeast. This will allow
for rising heights across the Desert Southwest with 500mb heights
of 592-595dm for Tuesday and Wednesday. The higher heights and
drier air will easily allow temperatures to warm to above normal
as early as Monday, but especially Tuesday through Thursday. Highs
by Tuesday should be hitting or even topping 110 degrees across
the lower deserts with an Excessive Heat Watch possibly being
needed on Tuesday with more of a likelihood on Wednesday. The
heat should persist into at least Thursday, after which there are
some indications of moisture seeping back into portions of at
least southeast Arizona late in the week. A weak inverted trough
loosely associated with a PV fracture that splits off from the
longwave trough and front over the eastern half of the U.S. on
Wednesday may eventually move west along the southern fringe of
the ridge to improve rainfall chances over Arizona by next Friday
.AVIATION...Updated at 0000 UTC.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A large upper disturbance was currently located over southeast
Arizona, moving slowly towards the northeast. Most of the forcing
should keep showers/storms off to the east of the terminals tonight
but still expect at least isolated showers from 02z through 08z or
so. Do not expect thunder at the terminals tonight but chances are
not zero. As of 5 pm a few weak storms were near Ak-Chin and moving
north but they will likely dissipate before getting into the
Main impact weather wise will be outflow winds, initially mainly
from the south and up to around 30kt, but they could vary between
southeast and southwest over the next 2-3 hours. After 03z, winds
should mainly focus out of the east/southeast and should dissipate
below 20kt. Overnight may see some lower cloud decks - down to
around 5k feet - develop with wrap around moisture coming into the
area, but any CIGs likely to stay at 8k and above. For tomorrow
should see thinning moisture and little if any chance for precip.
Mainly FEW-SCT decks from 6k to 9k feet across the central deserts.
Southeast California/Southwest Arizona including KIPL and KBLH:
No significant aviation impacts expected over the next 24 hours. Dry
southwest flow aloft will keep skies generally clear. Look for winds
to favor the south to southwest at KBLH with some afternoon south
breeze to near 20kt possible. Winds to favor the southwest/west
tonight at KIPL becoming light variable or light southeast during
the day on Sunday.
Aviation Discussion not updated for amended TAFs.
Tuesday through Saturday:
A much drier pattern is expected for most of next week with very
few thunderstorms expected even over higher terrain locations.
Temperatures will warm several degrees above normal amidst the
drier air mass, with winds following typical diurnal trends.
Humidity values will generally drop into the upper single digits
to mid-teens across the lower deserts while remaining above 20
percent over the higher terrain every day except on Wednesday.
Overnight recovery will generally be poor to fair except at higher
elevations where better recovery is expected. Moisture will begin
to increase on Friday or Saturday as moist southerly flow aloft
and isolated thunderstorms at higher elevations return.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
AZ...Flash Flood Watch until 5 am MST Sunday for AZZ552-556-558-