-- Discussion containing changed information from previous version are highlighted. --
814
FXUS63 KIND 252307
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
707 PM EDT Tue Jun 25 2024

.KEY MESSAGES...

- Thunderstorms will be around at times today into Wednesday. Some
  severe storms are possible, especially this afternoon.
- Severe storm chances remain overnight, but greater uncertainty
  exists with timing and potential.
- Today will likely be the warmest day of the week.
- A brief respite from heat and humidity Thursday before another
  warm up and additional storm chances this weekend.

&&

.MESOSCALE UPDATE...
Issued at 352 PM EDT Tue Jun 25 2024

A thunderstorm complex has recently entered central Indiana from
Illinois. In the past hour, these storms have evolved into an MCS
which has began propagating southeastward. Latest radar data has
shown a slight weakening trend within the past few scans, with the
strongest cell over Owen County as of 3:45pm.

Storms are advancing into an environment characterized by strong
instability (CAPE near 3000 J/Kg) and modest shear (25 to 35 knots).
A north-south CAPE gradient is found through the state of Indiana,
with diminishing instability as one heads east. Additionally, shear
decreases with southward extent.

Going forward, we can therefore expect that this system becomes
outflow dominant with time. Consequently, this likely leads to a
diminishing severe threat as well. However, soundings (ACARS and
model) show very deep CAPE profiles and steep lapse rates (7.5
C/Km). As such, occasionally strong updrafts may develop from time
to time as the system progresses southeastward. Strong wind gusts
and large hail are possible with the strongest cells.

Further north, a distinct outflow boundary is seen from Bloomington
Indiana eastward to the Ohio border. Very stable air exists north of
this boundary, characterized by CIN around -300 J/Kg. Storm
development north of this boundary is unlikely though lingering
stratiform rain is possible.

As a side note, additional storms are possible overnight as
instability advects back into the area behind the ongoing convective
system. Uncertainty remains with this, however, as ongoing
convection continues to alter the atmospheric thermodynamic profile.

&&

.SHORT TERM (This evening through Wednesday)...
Issued at 301 PM EDT Tue Jun 25 2024

We have a rather complicated short term forecast today due to
ongoing and expected convection.

THIS AFTERNOON

An MCS has been dropping south through the CWA this morning and into
the afternoon. Overall, a weakening trend has been observed with
most of the line dissipating completely. Two clusters, one near the
Ohio border and one just west of the Illinois border, remain.

The western cluster, currently near Charleston Illinois, or just
northwest of Terre Haute Indiana, is the most problematic for
central Indiana. As they propagate eastward, they will encounter an
increasingly unstable environment and further intensification is
likely.

MESOSCALE ENVIRONMENT

Across southwestern central Indiana, temperatures have climbed into
the upper 80s and lower 90s. Dew points are generally in the high
60s or lower 70s. Brisk southwesterly flow has been advection this
hot and humid air mass deeper into Indiana through the day. SPC
mesoanalysis shows upwards of 3000 J/Kg CAPE near Terre Haute.
Available CAPE decreases with eastward extent, with a distinct
instability gradient from Indianapolis down to Evansville.

ACARS soundings out of IND have shown an increasingly unstable air
mass with time. As of 18z, roughly 1800 J/Kg has been measured with
steep lapse rates of around 7.5 C/Km. The CAPE profile itself is
fairly wide, and extends to roughly 10km agl. This, combined with
DCAPE around 1000J/kg, would imply a wind and large hail threat.
Hodographs are short, with shear concentrated in the lower levels
(this may be from an outflow boundary that recently passed through
IND, however). SPC mesoanalysis shows less low-level shear south of
the boundary (under 20kt).

The aforementioned boundary extends from just north of Terre Haute,
southeastward through Martinsville, and then off into Ohio from
there. This boundary, with very unstable air located to its north,
may become a focused area for convective propagation as the Illinois
storm cluster builds eastward/southeastward. Additionally, storms may
preferentially propagate southwestward into the low-level flow. This
should lead to a generally south-southeastward system motion with
time, with areas north of the outflow boundary having less of a
chance of seeing strong to severe storms.

CONVECTIVE HAZARDS AND TIMING

Storms are ongoing just west of our border across Illinois, and
should be in our CWA within the hour. Terre Haute, for instance, may
see storms arrive between 3-4pm. Activity should then spread
southeastward, and potentially increase in speed if a mature cold
pool can develop. Latest HRRR shows storms exiting our area to the
southeast by around 8pm.

As for hazards, strong winds and large hail are the initial threats.
Should a cold pool develop, the threat will evolve into primarily a
wind threat. Additionally, training thunderstorms could lead to a
flooding threat.

TONIGHT

Guidance is insistent on storms redeveloping to our northwest
overnight and moving southeast into our CWA after midnight. This is
separate from the ongoing storms mentioned above. However,
uncertainty here is much greater due to the ongoing activity.
Current storms should thermodynamically alter the environment which
may change how subsequent storms develop and evolve. We will include
chance PoPs through the night which will be refined as the mesoscale
setup becomes clearer. Likewise, temperatures depend on how
convection develops but most locations will see lows in the high 60s
overnight.

WEDNESDAY

Tomorrow looks to be a cooler and cloudier day as a mid-level vort
max (and associated surface reflection) moves across central
Indiana. As moisture continues to advect into the region overnight,
precip chances will increase and become widespread due to the
synoptic scale forcing associated with the system. We will cap
precip chances at 80 percent due to the scattered convective nature
of the precipitation. Severe weather is not expected due to lower
shear and lower instability, but a low probability flooding threat
may remain.

&&

.LONG TERM (Wednesday night through Tuesday)...
Issued at 301 PM EDT Tue Jun 25 2024

Wednesday night through Thursday night...

The long term period will start off quiet and pleasant as surface
high pressure builds in behind a cold front settling south of the
region. Look for temperatures to remain near or slightly below
normal with weak cold air advection in place. Temperatures should
range from the upper 70s to low 80s for most areas. Far southern
counties may warm up into the mid 80s. Lower humidity on top of the
cooler temperatures will feel quite refreshing compared to the
hotter temperatures this past week. Expect light winds during this
period due to a weak pressure gradient.

Friday through Saturday...

Much of the day Friday is expected to remain quiet with surface
ridging in place initially. Late Friday into Saturday a surface low
and parent trough will move through the region with rain and storms
likely. The best chance for precipitation should be during the
Saturday once the cold front approaches. Daytime heating and
increasing moisture advection ahead of the front is expected to
promote moderate destabilization. This combined with weak to modest
effective bulk shear may support a few strong to severe storms. The
primary threat would likely be isolated damaging wind gusts, but
localized flooding or severe hail cannot be ruled out. Increasing
S/SW flow ahead of the aforementioned system will lead to warming
temperatures. Highs are likely going to be in the upper 80s to low
90s by Saturday.

Saturday night onward...

Precipitation chances linger overnight Saturday before drier
conditions return Sunday as the aforementioned cold front exits the
region. Surface high pressure building in should provide mundane
weather conditions Sunday and Monday along with cooler temperatures
from cold air advection.Another system may approach by Tuesday
bringing additional chances for precipitation, but diverging model
solutions leads to low confidence in this potential.

&&

.AVIATION (00Z TAF Issuance)...
-- Changed Discussion --
Issued at 707 PM EDT Tue Jun 25 2024

Impacts:

- Thunderstorms possible after 04Z tonight. Greatest Confidence over
  KHUF

- Additional thunderstorms possible tomorrow from 14Z through 00Z

- Potential for MVFR or worse conditions in thunderstorms, VFR
conditions likely outside storms

Discussion:

Low-moderate forecast confidence due to uncertainty in convective
development through tonight, as each round of convection will have
an impact on the next.

A cluster of storms currently over central IL will continue to
organize and move towards central Indiana. These storms could
potentially impact all TAF sites between 04-10Z overnight. There is
potential for MVFR or worse conditions in any thunderstorms. Outside
of convection, VFR conditions are expected.

More thunderstorms are expected to develop ahead of a boundary
tomorrow, with periods of MVFR or worse conditions within storms.
Following boundary passage winds will quickly shift towards NNW/N.
-- End Changed Discussion --

&&

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

$$

SHORT TERM...Eckhoff
LONG TERM...Melo
AVIATION...Updike