Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/05/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 1020 PM EDT Mon Sep 4 2023

.Forecast Update...
Issued at 1020 PM EDT Mon Sep 4 2023

Little change made to the forecast with this evening`s update. Main
focus over the next day will be the chance for storms tomorrow.

Latest surface analysis shows high pressure centered over the Mid
Atlantic states and an upper low pushing northward into Missouri.
This places Indiana within a region of warm and moist air advection
with persistent southerly flow. Satellite imagery shows mainly clear
skies over Central Indiana at the moment; however expect high clouds
to increase later tonight as the upper low and associated storms to
push closer to the region. Radar shows an area of showers and storms
moving northward into Southern Illinois; however IND ACARS soundings
suggest the column is still way too dry for any shower or storm
activity to reach Indiana this evening or during the overnight
hours.

Lift and moisture increase tomorrow as the upper wave pushes closer
to the Ohio Valley sparking off scattered showers and storms late
morning through the evening hours in such a hot and humid
environment. With surface dew points solidly in the 70s and
temperatures expected to remain in the 80s to near 90, CAPE values
should increase during the day towards 2000+ J/kg... a conducive
environment for shower and thunderstorm activity. Severe weather is
not expected at this time as wind shear will be relatively weak,
keeping storms more vertically stacked and short lived. Main threats
tomorrow will be periods of heavy rain, lightning, gusty winds, and
minor flooding possible. Due to such dry ground and lack of rain
lately, flooding is not a huge issue, but would not be surprised to
see very heavy rainfall rates leading to localized areas of minor
flooding. Storms should be scattered in nature so not expecting a
washout of a day. It will likely feel like the middle of summer
rather than early September with very warm, muggy conditions and
partly to mostly cloudy skies outside of storms. Overall, the state
will be getting much needed rainfall after the recent hot spells
over the past month. Additional thunderstorms are expected late
tomorrow night and then again on Wednesday, more info on that in the
long term section of the discussion.

&&

.Short Term...(This evening through Tuesday)
Issued at 231 PM EDT Mon Sep 4 2023

A warm and humid Labor Day ongoing for central Indiana with a
healthy cu field over much of the region. As anticipated...isolated
showers have developed along the leading edge of the moisture plume
expanding into the Ohio Valley from the southwest...from east
central Illinois northeast into the northern Wabash Valley. The
clouds had limited the heat a bit...but still had temps ranging from
the mid 80s to the lower 90s at 18Z.

The forecast continues to evolve away from the multi day period of
heat and humidity which just a few days ago appeared likely to
linger throughout the week. However with the ridging aloft and at
the surface already focused to our east today and the upper low
currently over eastern Oklahoma poised to lift into the area
Tuesday...this afternoon may be the last opportunity to hit 90 in
this stretch of hotter weather. The expansion of clouds and better
convective chances beginning Tuesday and continuing through midweek
appears increasingly likely to bring an abrupt end to the warmer
temperatures experienced over the last few days with more a seasonal
airmass to follow for later this week.

For the rest of the afternoon...expect sun intermingled with cu with
isolated showers remaining focused over the Wabash Valley and
especially between KLAF and KHUF. As mentioned earlier today...poor
mid level lapse rates and a lingering cap in the 800-750mb layer
will limit convective depth and likely keep any cells from being
able to achieve glaciation and the potential for lightning. MOst
will remain dry but a few brief...localized downpours will be
possible into the early evening before diminishing. Humidity levels
will remain high with dewpoints largely in the upper 60s and lower
70s. Skies may briefly clear this evening as cu dissipates with
sunset but moist advection will persist into the overnight with mid
and high level clouds expected in greater abundance than the last
few nights.

A vort rotating around the upper low was generating convection over
east Texas this afternoon. This feature will drift northeast on the
lee side of the upper low and should reach the lower Ohio Valley
near daybreak Tuesday. Model differences remain with respect to
timing of the feature but there is a consensus of the mid level vort
tracking across the region and serving as a potential catalyst for
renewed convective development across the forecast area by midday
Tuesday into the afternoon. While the upper low will be in the
process of weakening into an open wave...it will finally serve to
cool the mid and upper levels and interact with increasing low level
moisture to produce a modest unstable environment for convection to
form. Overall BL shear is very weak and mid level lapse rates in
particular remain unimpressive...suggestive that convection will
likely pulse in intensity in a somewhat disorganized state. In other
words...the threat for severe potential is low and likely will only
be achieved if a core aloft can briefly intensify enough to generate
a stronger downburst. That being said...potential is there for the
best chance for scattered storms across much of the forecast area in
a while.

Temps...the increase in clouds with a moist airmass should keep lows
largely in the low to mid 70s tonight. Low level thermals support
highs in the mid to upper 80s...but should convection develop
faster...these temperatures would need to be pulled back a few
degrees.

&&

.Long Term...(Tuesday night through Monday)
Issued at 231 PM EDT Mon Sep 4 2023

Tuesday Night Through Wednesday.

Conditions will remain active Tuesday night into Wednesday with a
weakening upper level low pressure coming in from the southwest
Tuesday night while a stronger system moves across the Upper Midwest
Wednesday into Wednesday night with a surface front stretching into
Indiana. Weak isentropic lift combined with forcing from the initial
upper level low will bring isolated to scattered showers to central
Indiana during the overnight hours Tuesday but most models keep the
strongest portion of the LLJ over Illinois vs Indiana with the GFS
being an outlier and the model that shows the most widespread
precipitation.

The cold front is expected to move through during the daytime hours
Wednesday with modest instability just ahead of the front but weak
shear. The lack of shear will limit the severe threat with storms
struggling to maintain organization. Primary hazard appears to be
quick downbursts causing isolated wind damage. The front should be
completely through by the early overnight hours with quiet weather
returning to central Indiana for the rest of the work week into the
weekend.

Thursday Through Monday.

Cooler weather will arrive in the aftermath of the frontal passage
with daytime hours with highs in the 70s to low 80s and lows
generally in the 50s Thursday through the weekend. Northwesterly
flow with a broad trough will dominate the upper level patterns
through this timeframe with a robust ridge across the Atlantic
trapping the trough across the Great Lakes.

&&

.Aviation...(00Z TAF Issuance)
Issued at 752 PM EDT Mon Sep 4 2023

Impacts:

* VFR conditions tonight
* Scattered showers & storms expected beginning tomorrow afternoon

Discussion:

Mainly VFR conditions expected tonight; however the weather becomes
active again tomorrow afternoon with storm chances persisting into
Wednesday.

For this evening and tonight, expect increasing high clouds
associated with a weakening area of storms in Missouri and Illinois.
As the weak system to the southwest approaches, expect winds to back
toward 160-180 degrees overnight remaining elavated around 5 kts.
Winds then turn back towards 200 degrees during the day tomorrow
increasing to around 10 kts with gusts upwards of 20 kts. Wind
speeds and direction may vary greatly through during showers or
storms.

The chance for storms increases late Tuesday morning from south to
north as storm system to the southwest continues to push northward
towards the region. Added VCSH starting around 15z in the south and
18z northward at KLAF with no ending time as scattered showers and
storms may be in the region through at least 00z. Conditions will
likely fluctuate between VFR, MVFR, and IFR as storms will be
scattered in nature, so timing of exact storms will have to be
monitored closely for much of the day tomorrow. At the moment not
expecting severe weather as wind shear is very weak; however brief
periods of heavy rain, lightning, gusty winds/ erratic wind
directions, and lower cigs and vis are all expected at times. A
brief break in the storms is expected after 00z tomorrow night
before more storms push in from the west after 07z.


&&

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

$$

Update...CM
Short Term...Ryan
Long Term...White
Aviation...CM



Area Forecast Discussion

National Weather Service Phoenix AZ

 408 PM MST Mon Sep 4 2023

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
Tranquil weather conditions will prevail throughout the week as
temperatures steadily warm back above the seasonal normal. In fact,
readings could potentially reach record levels by this weekend along
with a major Heat Risk. Rainfall chances will become neglible for at
least the next week.

&&

.DISCUSSION...
Seasonally strong troughing has swept into the central Rockies early
this afternoon resulting in deep westerly flow enveloping the SW
Conus. This trough passage has also displaced subtropical ridging
well into northern Mexico such that the westerly flow regime will be
persistent through at least the next several days. Although surface
dewpoints through south-central AZ remain in the lower/middle 60s,
this is a bit of a mirage as in-situ aircraft and model sounding
data has sampled extremely dry air above the H8 layer which will
erode this boundary layer moisture once mechanical mixing deepens
this afternoon. This trend of moisture erosion will only be
accelerated the next 36 hours such that low level mixing ratios
descend into a 4-7 g/kg range, and afternoon dewpoints possibly
reaching as low as the 30s in some locations. Not surprisingly with
this type of dessication, rainfall chances will be essentially be
nil throughout the remainder of the week.

Global ensembles indicate that the aforementioned trough will eject
into the eastern Conus later this week allowing subtropical ridging
to strengthen and build north from Mexico. H5 heights initially in a
586-590dm range will slowly increase as the anti-cyclone center
become stationed along the international border near El Paso. While
there is some model uncertainty with respect to the magnitude and
expanse of the ridge, confidence is excellent that temperatures will
spike back above normal during the latter half of the week. Ensemble
guidance spread remains rather narrow suggesting some locations
flirting with record highs (see Climate section) this weekend
coincident with the highest H5 heights edging into the forecast
area. However, these near record values may be short lived as
renewed zonal Pacific jet energy could act to dampen the ridge again
next week allowing temperatures to retreat back closer to normal.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No weather concerns will exist through Tuesday afternoon under
mostly clear skies. W/SW winds will continue into this evening
with a few brief gusts 15-20kt through sunset. Otherwise, the
typical late night easterly wind switch should be more evident
tonight across the entire metro.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist through Tuesday afternoon
under clear skies. Winds will be much lighter than the past couple
days with a north component favored at KBLH and westerly
direction at KIPL.

&&

.FIRE WEATHER...
Temperatures will warm back above the seasonal normal during the
latter half of the week as moisture levels continue to decline to
the point where rainfall chances essentially become zero for the
entire time frame. Minimum daytime humidity values around 15-25%
early in the week will solidly fall into the teens late this week.
Meanwhile, fair to good overnight recovery 40-60% should retreat
into a 25-40%. Other than some occasional afternoon upslope
breeziness, winds will follow typical diurnal tendencies.

&&

.CLIMATE...

Record highs:

Date        Phoenix          Yuma         El Centro
----        -------          ----         ---------
Sep 8     110 in 1979     115 in 1979    114 in 2018
Sep 9     111 in 2021     113 in 1990    115 in 1968
Sep 10    111 in 1990     114 in 1979    113 in 1971

&&

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

$$

DISCUSSION...18/RW
AVIATION...18/Kuhlman
FIRE WEATHER...18/RW
CLIMATE...18