Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/12/22

Area Forecast Discussion

National Weather Service Indianapolis IN

 1159 PM EDT Mon Jul 11 2022

...Updated Aviation Discussion...

.Mesoscale Update...
Issued at 1158 PM EDT Mon Jul 11 2022

Storms continue to struggle to maintain themselves in the
unfavorable low level thermodynamic environment.  Latest ACARs
soundings over IND show a persistent cap with MLCIN numbers over 500
J/kg.  Above this cap though, favorable lapse rates and modest
instability are allowing for storms to initiate along the front
where forcing is pushing parcels through the cap.  The more robust
CAPE is over into central Illinois where storms have been able to
maintain themselves more effectively.

Overall don`t expect too much to occur over the next few hours as
the front continues to push into the area, but if storms are able to
build and tap into the instability, moderate shear in the low to mid
levels may allow for briefly stronger storms.  Damaging winds aloft
should struggle to reach the ground with the poor lapse rates near
the surface and high LCLs will limit any tornadic threat even though
shear from 0-1km is around 20kts.

&&

.Forecast Update...
Issued at 1030 PM EDT Mon Jul 11 2022

Surface observations show that winds have started to shift in the
far NW corner of the forecast area where the weak cold front lies.
As of writing this, no precipitation has formed along the boundary
within or around central Indiana. CAMs are still showing showers and
thunderstorms forming as the front progresses through the area so
could see storms forming over the next hour or so. Forecast was in
good shape, the main updates made were minor adjustment to PoPs,
lowering them for the first few hours but keeping scattered
mentioned through the overnight hours before ending around the
morning rush hour.

&&

.Short Term...(This evening through Tuesday night)
Issued at 248 PM EDT Mon Jul 11 2022

* Showers and thunderstorms possible tonight, a few of which could
  be strong to severe.

* Quiet and slightly milder weather remainder of the short term.

A weak cold front will sag through the area tonight. Guidance
indicates showers and thunderstorms should form along this boundary
late this evening as it moves into the area, but uncertainty remains
with respect to coverage and intensity, particularly with southward
extent.

Ample moisture is present ahead of the boundary, with model
precipitable water values in excess of the 90th percentile of
climatology, however combination of at least modest storm motions
and the southward motion of the boundary should combine to limit
precipitation time in any one location. Marginal day one excessive
rainfall outlook is reasonable given the deep moisture.

Shear is also fairly modest at best and mostly unidirectional, which
along with unfavorable diurnal timing of frontal passage should
limit the extent of the severe threat. There will be at least
moderate instability, but gradually stabilizing low levels will work
against more widespread damaging wind threat. Marginal/slight day
one severe outlook is reasonable.

Convection should be weakening with time as it sags along the
boundary to the south/southeast, and most guidance indicates
activity should be coming to an end by daybreak Tuesday - so will go
with a dry forecast tomorrow into tomorrow night. A weak shortwave
does skirt the area Tuesday night but given forecast profiles will
likely only result in a slight increase in cloud cover.

Temperatures tonight will likely bottom out in the upper 60s to low
70s given increasing cloud cover and high dewpoints ahead of the
front. This is roughly in line with blended guidance. Tuesday highs
were nudged up a bit as ample sunshine and drier air in the low
levels will likely allow temps to easily rise into the mid 80s
across the area. Lows Tuesday night will be a bit cooler, again
given the drier low levels and decent radiational cooling conditions.

&&

.Long Term...(Wednesday through Monday)
Issued at 248 PM EDT Mon Jul 11 2022

Tuesday night through Friday night

A 500mb ridge will continue to sit over the western portion of the
United States, slowly creeping eastward towards our CWA. Winds will
shift northerly on Wednesday following the passing of a cold front
earlier this week. This northerly flow will drop dew points to the
mid to upper 50s on Wednesday and Thursday night, about 10 degrees
below average. High temperatures will remain seasonable through
Friday, as dry air advected from the Upper Great Plains drops dew
points into the mid to upper 50s. Ahead of the next low pressure
system, winds will shift westerly and remain light

Saturday through Monday

A shortwave trough will develop along the upper level ridge and
march towards the Eastern Great Lakes during the weekend. Models are
hinting that this shortwave trough will be a weak 500mb closed low.
With CIN being weaker along the peripheral of the ridge, the low
will tap into instability associated with warm air over the surface
of the Great Plains. The warm air will support significant mixing
between the surface and mid levels. However, this low pressure
system will not have a favorable structure for strengthening since
the surface low will be vertically stacked with its parent low. WAA
in the warm sector of the low pressure system will increase heat
indices to the upper 80s and lower 90s going into the weekend.
Modestly moist air from the Great Lakes will be advected into our
CWA by a northerly flow aloft.

During the passing of the cold front, models show CAPE in excess of
2,000 J/kg with minimal shear in both the upper and lower levels.
The highest CAPE values and most favorable LI indices are trending
towards southeastern-central Indiana, where severe weather would be
most likely. The GFS is showing 1.50 inches of precipitable water as
the front moves through, only about 0.30 inches above our
climatological average for this time of year, so significant
rainfall amounts are not likely.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1158 PM EDT Mon Jul 11 2022

IMPACTS:

* Winds veering tonight to become northwesterly by midmorning with
  wind speeds of 7 to 15 kts

* Showers and a few thunderstorms overnight

Discussion:

VFR conditions should dominate through most of the period. A weak
cold front will sag south through the area tonight, producing
scattered showers and thunderstorms, a few of which may be strong.
Isolated storms have started forming over the area but have been
very pulsey thus far. The threat for storms have already ended at
KLAF but will potentially impact the rest of the TAF sites
through the early morning hours. Brief restrictions will be
possible with shower/storm impacts, but VFR should predominate.

Sustained winds will be around 5-10 kts tonight, and a few gusts are
possible but should be sporadic enough to preclude a prevailing
mention. Winds will be changing direction to northwesterly as the
weak front passes.

&&

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

$$

Mesoscale...White
Update...KH
Short Term...Nield/Marcus
Long Term...AM/Monaghan
Aviation...KH



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 909 PM CDT Mon Jul 11 2022

.UPDATE...
Issued at 909 PM CDT Mon Jul 11 2022

Confidence continues to diminish in footprint of convective
potential this evening, however ample conditional instability and
deep layer shear combo would continue to suggest that any decent
storms that manage to develop could present a damaging wind threat.
At this time, it would appear the best potential for isolated to
scattered thunderstorm development would be with an outflow boundary
pushing south-southeastward from storms over southeast WI, or
along/ahead of weak cold front roughly along/south of the I-80
corridor.

At 845 pm, radar depicted an area of scattered thunderstorms over
far southeast WI and parts of southern Lake Michigan, moving to the
east over the lake. These storms were producing an outflow boundary,
which was pushing to the south-southeast at around 20 kt however,
which looks to move into far northeast IL around 930 pm. SPC
mesoanalysis data estimates 1000-2000 J/kg of MLCAPE was in place
across northeast IL ahead of this boundary, with an aircraft ascent
sounding KMDW at 0045Z modified for current surface conditions
yielding around 1300 J/kg though with weak capping between 900-800
mb. Convergence along the outflow boundary may be able to initiate
isolated convective updrafts as it pushes south into northeast IL
after 930 pm, though even this may not be able to overcome the weak
low level lapse rates/capping. Thus confidence in convective
initiation is low.

If isolated storms are able to initiate however, either along the
outflow boundary or the weak cold front along/south of the I-80
corridor, MUCAPEs of AOA 2000 J/kg and effective deep shear of 50-55
kts would support the potential for organization (supercell
structure earlier with storm which passed across northern Cook
county late this afternoon). Largely unidirectional shear and weak
low level lapse rates would support mainly a damaging wind risk,
though again would expect overall coverage to remain fairly limited.
SPC has maintained a slight (level 2 of 5) risk with their 01Z
update through the remainder of the evening hours across roughly the
southeast half of the cwa for this possibility, though expect that
any such threat would be very isolated. It`s entirely possible no
storms develop at all. Isolated thunderstorm threat should end after
midnight, as the weak cold front sags southeast of the forecast
area.

Ratzer

&&

.SHORT TERM...
Issued at 1209 PM CDT Mon Jul 11 2022

Through Tonight...

Looking forward to this afternoon and evening, our main forcing
mechanisms will approach from the north and west. A fairly anomalous
upper trough over the upper Midwest will spread southeastward and
steer a cold front toward the upper Mississippi valley. Height falls
ahead of the trough, right entrance of the jet core ahead of the
trough and the front will all work to weaken a the cap -- and near
term guidance suggest the first attempt at this will be closer to
this forcing in northern/northeast Illinois and maybe more so into
Wisconsin. The cap will take more time to erode in our south.

Current uncertainty centers on this mid level cloud cover, but IR
satellite indicates some decent warming aloft, and we have low level
moisture increasing from the south and west, so there still appears
to be a window over northeast Illinois for severe storms. We expect
there will be convective attempts this afternoon, but the window may
be fairly narrow. Both the RAP and HRRR suggests the cap erodes but
differ as to the degree of instability at that point, and the HRRR
window of weak capping is quite narrow, and even the RAP which was
more aggressive in its earlier runs has backed away, likely a result
of some latching on to the worked over environment. We may have to
watch for some decaying storms that form in Wisconsin that drift
southeast this evening.

The instability axis gets shifted south of the I-80 corridor pretty
quickly late this afternoon and evening ahead of the remnant
boundary form this morning and any lingering differential heating
boundary. With this in mind, the SPC Slight Risk (Level 2/5) area
has been focused out ahead of these boundaries. This is the area
that stands the best chance of a few scattered severe storms mainly
in the evening hours once the upper forcing makes further
southeastward progress.  Damaging winds would be main hazard with a
2,000+ J/Kg of MLCAPE and some 40-50 kt of deep layer shear, but
there still remains some uncertainty as to the best corridor of
storm development. Drier air will filter in behind the front/trough
later tonight and end of the storm threat.

KMD

&&

.LONG TERM...
Issued at 258 PM CDT Mon Jul 11 2022

Tuesday through Monday...

Following this evenings cold frontal passage and potential period
of active weather breezy northwesterly winds on Tuesday will
transport a drier and cooler air mass into the area. This cooler
and drier airmass is likely to persist across the area through
later in the week as as upper level troughing (cyclonic upper
flow) sets up over the Great Lakes. This will generally result in
pleasant weather continues each day, with inland highs generally
in the lower 80s and lakeside highs in the 70s. Precipitation
chances through the Friday looks rather low. However, a couple of
minor weather disturbances, along with rather cool mid-level
temperatures will support diurnal cumulus development both
Tuesday and Wednesday afternoon, and possibly a few light widely
scattered showers. The slightly better chance for these showers
looks to be over far northern IL Tuesday afternoon and over inland
areas of northern IL Wednesday afternoon.

Surface high pressure is expected to settle over the Great Lakes
on Thursday, before shifting to the east late Friday and on
Saturday. While this will support pleasant and dry weather both
days, temperature and humidity values will begin to increase
into the weekend as the low level flow turns southerly following
the eastward departure of the surface high. The weather pattern also
may turn a bit more active and supportive for some clusters of
thunderstorms for at least a portion of weekend. This as an upper
level ridge over the west begins to build eastward into the
Plains and accordingly places our area right within an active belt
of northwesterly mid/upper level flow. Given the inherent
uncertainties with timing and placement at this timescale, we
continue to mention only low end chance POPs in the forecast
through the weekend.

KJB

&&

.AVIATION...
For the 00Z TAFs...

The primary aviation weather concerns through the 00Z TAF period are
as follows:

- Isolated showers and thunderstorms across the Chicago metro
through ~01Z

Isolated showers and potentially an additional thunderstorm or two
remain possible in the vicinity of the Chicagoland terminals through
roughly 01Z this evening. There exists a small potential for
additional rainfall moving over the area through as late as 03Z,
though confidence and expected coverage is far too low to include in
the TAF. Following the rain potential, skies should be mostly clear
and gusty westerly winds will begin steadily subsiding. Through the
night, winds should average at around or just over 10 kts. Another
breezy day on Tuesday will feature gusts near 20 kts from the late
morning through mid-evening while winds blow in from the WNW. Winds
will then subside to under 10 kts for the last few hours of the
extended TAF period. VFR conditions can be expected through the
entirety of the period.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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