Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/12/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 930 PM EDT Thu May 11 2023

.Forecast Update...
Issued at 930 PM EDT Thu May 11 2023

Mid and high level clouds continue to overspread the region from the
southwest this evening ahead of a warm front approaching. 01Z
temperatures largely remained in the 70s.

The main focus for the evening update is to reevaluate precip onset
as an abundance of dry air lingers over the region. Current IND
ACARS sounding shows dry air below 600mb and the persistent
southeast flow will at a minimum slow moisture advection into the
forecast area for the next several hours. Have scaled back any rain
mention to the lower Wabash Valley through 06Z and even there...any
rain will be light and sparse in coverage.

Beyond 06Z...a more concerted push of moisture into the area will
arrive courtesy of weak but noted isentropic lift and a general
increase in 850mb flow from the south. With the warm front moving
into the lower Ohio Valley during the predawn hours and aiding
lift...expect isolated to scattered convection to increase through
daybreak from southwest to northeast.

Overnight lows in the 60s look reasonable and were not adjusted.
Zone and grid updates out.

&&

.Short Term...(This evening through Friday)
Issued at 301 PM EDT Thu May 11 2023

* Chances for rain at times through Friday. Some thunder possible,
  but severe storms are not expected.

Early this afternoon, skies were partly cloudy across central
Indiana as moisture begins to return to the area. The lower levels
of the atmosphere remain dry across much of the area, which is
helping to dry up any rain as it tries to enter central Indiana from
the southwest.

Rest of this afternoon...

In general clouds will continue to gradually increase across central
Indiana. Weak lift could generate an isolated shower or storm,
especially where some weak instability will have built across the
southwest and far southern forecast area. Will go with low PoPs
there. Warm temperatures will continue.

Tonight...

Instability will diminish this evening with loss of heating,
allowing any convection that developed to weaken and dissipate. Will
keep some low PoPs mainly across the southwest forecast area.

During the night as a surface warm front moves across the area and
an upper trough approaches, some additional showers and perhaps a
thunderstorm may develop. Forcing isn`t great so will keep PoPs in
the chance category.

With the more humid air moving in, temperatures will be warmer than
previous nights, with lows in the 60s.

Friday...

Overall lift looks a little better on Friday with an upper trough,
and moisture will be good by then thanks to the warm front. Will go
with a period of likely PoPs most areas on Friday as the lift moves
through. Thunderstorms are possible, but severe storms are not
expected with better instability remaining out of the area.

Clouds and rain will keep temperatures lower than Thursday, but
highs will still reach the mid 70s to around 80.

&&

.Long Term...(Friday night through Thursday)
Issued at 301 PM EDT Thu May 11 2023

Scattered showers and storms will likely be ongoing at the start
of the period with continued low level theta-e advection and
isentropic ascent. Amplification of an upper ridge across the
central CONUS and mid level dry air advection should allow for
coverage of storms to diminish after daybreak Saturday. Scattered
diurnal convection is still expected though as daytime heating and
surface dewpoints in the upper 60s could yield MLCAPE values around
2500J/KG. Overall forcing on Saturday will be very weak, but
isolated damaging wind gusts cannot be ruled as mid level dry air
advection could enhance downburst potential. In addition, some
models are hinting at an MCS developing during the evening along a
low-level theta-e gradient over IL/IN and propagating southeast.
Confidence is low at this time due to the weakly forced environment,
but if an MCS were to develop, this would further enhance the
damaging wind threat. Low confidence remains regarding any severe
weather potential, but models should become better aligned in the
coming days. Will keep chance POPs into the overnight period to
account for this uncertainty.

More diurnal storms are expected on Sunday, but slightly greater
coverage is expected with PVA ahead of an approaching upper trough.
A cold front will begin to drift south late Sunday, pulling in
cooler/drier air across the north which may limit convection.
Further south, sufficient forcing and moderate instability will
result in scattered thunderstorms. Some models suggest the potential
for another MCS to develop by the evening, but a lot of uncertainty
remains. Timing of the front and uncertainty with convective
evolution on Saturday night will once again result in a low
confidence forecast.

Some convection may linger into Monday, but mostly dry and cool
conditions are expected next week as a cold front moves through.
Temperatures will be above average through Sunday before returning
to near seasonal early next week. A shortwave trough moving through
late Tuesday into Wednesday may bring some rain to portions of the
area, but limited moisture leads to some uncertainty.

&&

.Aviation...(00Z TAF Issuance)
Issued at 626 PM EDT Thu May 11 2023

Impacts:

* MVFR conditions developing Friday morning

* Scattered to numerous showers developing shortly before daybreak
  and continuing Friday. Isolated thunderstorms are possible.

Discussion:

The broad surface ridge centered along the east coast continues to
keep a dry airmass over the region early this evening with clouds
confined to expanding cirrus. Cloud coverage will gradually thicken
and lower tonight as a warm front approaches from the southwest...
but any rainfall will be limited by the presence of continued dry
air within the boundary layer until the predawn hours. Light
southeast winds are expected tonight.

As the warm front moves into the region early Friday and deeper
moisture and lift arrive...scattered to numerous areas of convection
will impact the terminals. Brief restrictions within heavier
convection is possible but model soundings favor the expansion of
MVFR ceilings as the front lifts north through the area. The front
will shift north of the terminals by mid to late afternoon with any
lingering convection decreasing in coverage along with improvements
in ceilings back to VFR levels. Lower ceilings may however return
Friday night. Winds will veer to southerly by Friday afternoon south
of the warm front.

&&

.IND WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Update...Ryan
Short Term...50
Long Term...Melo
Aviation...Ryan



Area Forecast Discussion...UPDATED

National Weather Service Los Angeles/Oxnard CA

 832 PM PDT Thu May 11 2023

.SYNOPSIS...11/553 PM.

Warming temperatures are expected through Saturday as onshore
flow weakens beneath ridging aloft. However, cooler temperatures
will persist near the coast with night through morning low clouds
and fog. Warmer than normal temperatures are then expected away
from the coast Sunday through much of next week.

&&

.SHORT TERM (THU-SUN)...11/831 PM.

***UPDATE***

Latest satellite and surface observations indicate clear skies
across the area this evening. AMDAR and Vandenberg sounding data
indicates marine inversion about 1000-1400 feet deep. As for
winds, northwesterly winds gusting 40-45 MPH currently blowing
across the southwestern Santa Ynez Range with lighter winds
elsewhere.

Forecast-wise for the immediate short term, main concerns will be
the Sundowner winds and marine layer stratus. Currently, Refugio
and Gaviota are gusting 40-45 MPH and should continue at these
levels overnight. So, current WIND ADVISORIES for these areas
looks good through 300 AM Friday. As for marine layer stratus, do
not anticipate any significant change in inversion depth
overnight. So, current onshore gradients should allow for some
stratus/fog to develop. Current forecast indicates stratus/fog
across the Central Coast of Santa Barbara county, the Salinas
River Valley as well as the coastal and coastal valleys areas of
Ventura/LA counties. Looking at latest HREF, this forecast of
areal coverage looks pretty good although there is a chance that
Ventura county could remain clear.

Overall, current forecast has good handle on the immediate short
term. So, no significant updates are anticipated.

***From Previous Discussion***

Weakening onshore flow and a building ridge aloft will lead to
warmer temperatures Fri/Sat, especially inland. Forecast
soundings show significant warming aloft with the marine inversion
shrinking to 1000 feet or less by Saturday. Coastal areas will
still be dealing with night and morning stratus and fog, most of
which should clear by afternoon, though there`s probably a 30
percent chance or so of clouds lingering at the beaches,
especially Sunday as onshore flow makes a brief resurgence. Warmer
valleys will pop up in to the lower 90s by Saturday, but then
cool a few degrees Sunday with the onshore return.

One last night of advisory level Sundowner winds across southwest
Santa Barbara County. Should be somewhat less windy than last
night as northerly gradients continue to weaken. Then much less
wind over the weekend as light southerly flow returns as well as
some coastal low clouds.

.LONG TERM (MON-THU)...11/210 PM.

Steady moderate onshore flow to the east expected through next
week while gradients to the north remain light or slightly
onshore. This is a typical May Gray pattern and expect a steady
dose of marine layer stratus each day, possibly with limited
clearing at the coast, particularly early in the week when the air
mass isn`t quite as warm due to the easterly wave passing into
northern California. Still looking at increasing moisture from the
east around the middle of the week as a ridge of high pressure
develops over the Great Basin and shifts the upper level flow to
east-southeast. PW`s increase from around half inch currently to
around 1 inch Wed-Fri next week. While the Canadian model backed
off the moisture on the 12z run, both the EPS and GEFS remained
pretty steady and enough to warrant at least a slight chance of
showers and thunderstorms across at least the eastern LA County
mountains. Warmer than normal temperatures expected to continue
inland through the week.

&&

.AVIATION...12/0049Z.

At 0018Z at KLAX, the marine layer depth was 1600 feet. The top
of the inversion was at 2700 feet with a temperature of 13
degrees C. There was another inversion between 3300 feet to 6700
feet with a temperature of 12 degrees C at the top.

Low to moderate confidence in the coastal/valley TAFs and high
confidence in the desert TAFs. The lowest confidence exists for
the Central Coast sites, where MVFR to IFR cigs could dissipate as
early as 14Z, and flight cat changes could be off by +/- 3 hours.
Further south, cigs are generally expected to be MVFR, but flight
category changes could still be off by +/- 2-3 hours. For the LA
Valley sites, there is a 20 percent chance of IFR cigs overnight.

KLAX...Moderate confidence in the 00Z TAF. Timing of flight cat
changes from VFR to MVFR could be off by up to 3 hours. Good
confidence any east wind component will remain under 6 kt.

KBUR...Low to moderate confidence in the 00Z TAF. Timing of
flight cat changes could be off by +/- 3 hours. There is a 20-30%
chance that conds will remain VFR overnight, or that CIGs could
lower to IFR overnight.

&&

.MARINE...11/817 PM.

For the Outer Waters, moderate to high confidence in current
forecast. Through Friday night, high confidence in Small Craft
Advisory (SCA) level winds. For Saturday there is a 40-60% chance
of SCA level winds continuing through late in the afternoon,
especially across PZZ670 and PZZ673. For Sunday and Monday, high
confidence in winds and seas remaining below SCA levels, but there
is a 30% chance of SCA level winds on Tuesday.

For the Inner Waters north of Point Sal, high confidence in
current forecast. SCA level winds will develop during the
afternoon-evening hours through Friday night. For Saturday
through Monday, high confidence in winds and seas below SCA
levels, then a 30 percent chance of SCA level winds on Tuesday.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. SCA level winds are beginning to
decrease across the western half of the Santa Barbara Channel.
There is a 60% chance of SCA level winds again for the afternoon
and evening hours Friday. Otherwise and elsewhere, high confidence
in winds and seas remaining below SCA levels through Tuesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect until 3 AM PDT Friday for zones
      349-351. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 5 PM PDT Saturday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 4 AM PDT Saturday for
      zone 676. (See LAXMWWLOX).

&&

$$

PUBLIC...MW/Thompson
AVIATION...Smith
MARINE...Smith
SYNOPSIS...MW/Smith

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox