Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/22/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 844 PM EDT Thu Sep 21 2023

.Forecast Update...
Issued at 844 PM EDT Thu Sep 21 2023

Radar loop was showing weakening showers lifting northeast over the
upper Wabash Valley. Somewhat stronger convection, including
lightning strikes per ENTNL lightning data, was well to the west of
the Wabash Valley within deeper moisture convergence. SPC
mesoanalysis page was showing dying instability over the Wabash
Valley. This trend will continue as the night goes on. So will only
keep small overnight PoPs there with much drier air to the east of I-
65.

IR satellite and obs were showing some breaks in the mid and high
clouds, but overall the clouds should keep fog from being a big
issue. The exception could be over the Ohio Valley if any extended
breaks occur there, but this is low confidence in occurring. The
light ESE winds should bring in slightly lower dew points which
combined with any breaks could allow temperatures to fall to the
upper 50s overnight over some locales.

&&

.Short Term...(This evening through Friday)
Issued at 300 PM EDT Thu Sep 21 2023

* Diminishing clouds tonight
* Warm last day of summer with highs in the 80s

.This evening and tonight...

Latest satellite and radar imagery this afternoon shows an upper
level low slowly retrograding into Iowa with its associated clouds
and showers extending eastward into Indiana. Thickest cloud cover and
showers have remained across the western two tier of counties along
the IL state line and should remain that way through the rest of the
evening. IND ACARS soundings has shown a sharp cut off in low level
moisture with the lowest 6km of the atmosphere too dry to support
showers along the I-65 corridor. Forcing for ascent and moisture
will begin to diminish this evening as the system continues to pull
north and west away from the region. Higher clouds may stick around
through the overnight hours, especially across the western portion of
the state, but expect a clearing trend tomorrow. Lows tonight are
slightly above guidance due to cloud cover limiting radiational
cooling. Keeping western portions of Indiana warmest in the lower
60s with eastern Indiana likely dropping into the upper 50s.

.Friday (Last Full Day of Summer)...

The official last full day of summer will feel quite warm across
Central Indiana as the upper level low loses influence over the
weather here locally. The state will be sandwiched into between the
developing low pressure system along the Front Range and the
developing tropical system off the coast of the Carolinas. High
pressure centered over the Northeast nudges itself southwestward
into the region leading to a fairly quiet and warm day. Clearing
skies should lead to ample warming of the boundary layer resulting
in above average highs in the 80s across the entire region.

&&

.Long Term...(Friday night through Thursday)
Issued at 306 PM EDT Thu Sep 21 2023

Friday Night through Sunday...

Dry and mostly clear conditions will prevail this weekend as central
Indiana finds itself under a weak yet stacked ridge...being squeezed
between a weaker plume of Gulf moisture back towards the Mississippi
River...and overcast conditions around the western periphery of a
tropical system progged to weaken over the Mid-Atlantic.  Light east-
northeasterly breezes will promote low humidity while skies trend
from plentiful sunshine Saturday to increasing clouds Sunday from
west to east as the ridge shifts to our northeast.

Temperatures will be slightly above normal yet pleasant...with highs
around 80F Saturday and in the upper 70s for most locations
Sunday...while lows exhibit a downward trend through the 50s.

Sunday night through Thursday...

Lower certainty exists with how the mid/upper levels will rearrange
over the central US/Midwest where the southern portions of a rather
disorganized, and probably weaker omega-style block attempt to set-
up.  Nevertheless recent guidance is showing at least moderate
confidence in an overall drier solution...with any blocking setting
up with a generally neutral tilt that would more likely keep the
block`s western short wave near the Dakotas or even farther north
into south-central Canada.

This would likely leave central Indiana in more of a doldrum south
of the blocking ridge with disorganized weaknesses floating
near/across the CWA.  Any low potential for rain could be best
realized Sunday night-Monday night with perhaps the only period of
organized precipitable water in the 0.80-1.30 inch realm...as this
formerly-tropical patch retrograded near the southern Midwest/Ohio
Valley from the southeastern portions of the upper block.

The block should break down through the mid-week with the small
eastern wave expanding and possibly absorbing the remnant western
wave while swinging it southeastward near Indiana. Can not rule out
isolated showers through this shifting and slightly disturbed
pattern.  Although the very broad surface high over much of eastern
North America should continue to suppress most Gulf moisture south
of the region, limiting rain potential.

Temperatures will exhibit an overall downward, albeit subtle, trend
from slightly above to near normal...with diurnal spreads of only 15-
20 degrees during the workweek courtesy of what should be low to
moderate humidity from the Mid-Atlantic tropical system.

&&

.Aviation...(00Z TAF Issuance)
Issued at 708 PM EDT Thu Sep 21 2023

Impacts:

- Convection possible with a small chance of MVFR flying conditions
through 03z at KLAF and KHUF

Discussion:

Mostly VFR flying conditions are expected through the TAF period.
Mid and high clouds should keep fog from forming tonight after the
showers dissipate not too long after sunset. Although, the
atmosphere was moderately unstable at KHUF late this afternoon, that
should quickly drop off at sunset and lightning has consistently
been well west of the Wabash Valley. So, feel thunder threat is too
low to put in the TAFs.

Winds will be ESE less than 10 knots.


&&

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

$$

Update...MK
Short Term...CM
Long Term...AGM
Aviation...MK



Area Forecast Discussion

National Weather Service Phoenix AZ

 509 PM MST Thu Sep 21 2023

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Temperatures across the region will hover slightly below normal the
remainder of the week before warming back to slightly above normal
early next week. Although dry conditions will persist, thicker
clouds cover will be common the next couple days before clearing by
the end of the weekend.

&&

.DISCUSSION...
The western Conus flow pattern early this afternoon can be
characterized by a deep negative PV anomaly spinning over eastern
Oregon forcing an unusually strong zonal jet core and modest height
falls through Arizona. ACARS in-situ soundings depict further
erosion of lower troposphere thermal profiles such that temperatures
across the area are starting to fall into a slightly below normal
range. In addition to the Oregon wave, a rather subtle East Pacific
circulation combined with the remnant moisture from TC Kenneth will
eject into the SW Conus Friday and Saturday resulting in expansive
thick high/mid cloud cover. While H5 heights near 585dm would alone
maintain temperatures a few degrees below normal the next 48 hours,
thick clouds may additionally restrict better surface insolation;
and it would not be a surprise if readings ended up a few degrees
below the required NBM output and at least 5F below the seasonal
average.

Early next week once the aforementioned Oregon and East Pacific
waves progress into the plains, ensemble members are in excellent
agreement that subtropical high pressure centered over Mexico will
nudge poleward pushing H5 heights at or above 588dm during the first
few days of next week. With minimal spread in numerical guidance,
forecast confidence is also excellent that temperatures will respond
by warming back a few degrees above normal. Another upper level
trough is forecast to develop over the Northern Pacific impacting
the Pacific Northwest and northern California through early next
week. This is where models begin to diverge through the latter half
of next week owing to resolving the breakdown/evolution of blocking
over the eastern Conus/SE Canada. More aggressive solutions rapidly
dig shortwave energy into the trough base carving out deeper
negative height anomalies over the Great Basin while others
piecemeal lower amplitude shortwaves zonally such that
midtropospheric heights only slowly deteriorate over the SW Conus.

&&

.AVIATION...Updated at 0009Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Westerly winds, with some gusts upwards of 15-20 kts, will
continue into the early evening hours before decoupling. Winds
will generally follow diurnal tendencies through the period. SCT-
BKN high level clouds will increase through this evening aoa 20-25
kft before SCT-BKN mid level clouds around 15 kft increase for
Friday morning. Hi-res guidance indicate the possibility of a few
virga showers by late Friday morning and into the afternoon, with
most of this expected to stay north of the TAF sites. Any virga
showers that do develop could lead to some localized breeziness.

Southeast California/Southwest Arizona including KIPL and KBLH:
Breezy west to southwest are expected to continue heading into the
evening hours at the terminals, with gusts upwards of around 25
kts, before tapering off. Winds will become light and variable at
KIPL during the overnight and morning hours Friday, while winds at
KBLH switch from a light NNW to SSW component. SCT-BKN high clouds
will increase through the evening and overnight hours before BKN-
OVC clouds aoa 15 kft increase by mid to late morning. Hi-res
guidance indicate the potential for passing virga showers and
perhaps a few sprinkles at the TAF sites by mid to late morning
but not enough to warrant VCSH in the TAFs at this time.

&&

.FIRE WEATHER...
Quiet weather conditions will continue through at least the middle
of next week with near zero chance for wetting rainfall.
Temperatures slightly below normal the remainder of this week will
warm back near the seasonal average next week. Afternoon humidity
values will mostly fall into the teens with fair to good overnight
recoveries of 30-60% this week, however larger expanses of single
digit minimum RH and poor recovery will begin to develop next week.
Locally breezy conditions today will give way to weaker winds the
remainder of the forecast period with more common modest afternoon
upslope gustiness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...18/Kuhlman
AVIATION...Smith
FIRE WEATHER...18/Kuhlman