701
FXUS63 KIND 041708
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
108 PM EDT Tue Jun 4 2024

.KEY MESSAGES...

- Warmer today and humid.

- Best chances for showers and thunderstorms Wed.

- Possible brief downpours will accompany thunderstorms Wed morning.

- Below normal temperatures in the 70s late week into the weekend

&&

.FORECAST UPDATE...
Issued at 959 AM EDT Tue Jun 4 2024

Scattered showers and thunderstorms are expected later this morning
through the evening hours across Central Indiana. Satellite imagery
shows an MCV over Central Missouri associated with a mid to upper
level wave and an associated boundary extending southeastward into
Southern Illinois and Western Kentucky.. Expect this feature to push
NNE through the afternoon hours with a boundary lifting northeast
into Indiana. Latest IND ACARs sounding still indicates a low level
inversion just above the surface with elevated CAPE around 300 j/kg,
weak mid level lapse rates near 500mb, and weak shear. The
environment south and west of the aforementioned boundary is
depicted nicely on the latest St. Louis ACARs sounding with surface
based CAPE near 900 j/kg already at this hour, a more saturated
column, and steeper mid level lapse rates. Expect the environment to
continue destabilizing across Central Indiana through the next few
hours and especially once the boundary pushes into the region
through the afternoon hours. DayCloudPhase Distinction RGB and
LightningCast tool show glaciating tops and lightning potential with
convection in Western Kentucky behind this boundary indicative of an
environment supportive of convective activity. The presence of the
MCV and boundary may result in earlier convective initiation for
Southern and Western Indiana than what guidance suggests as 00z-06z
guidance likely does not have a good handle on those mesoscale
features. Lowered highs for the south and western portion of the CWA
due to increasing cloud cover already and the presence of showers
near the IL/IN state line at this hour. Not too concerned with
severe weather potential for later this afternoon as shear is
relatively weak; however with the presence of this boundary and MCV,
an isolated strong to severe storm with damaging winds is not out of
the question, especially if a storm has deviant motion or merges
with another cell. Best chance of a stronger storm will be across
Western and Southern portions of Indiana, while Northern and Eastern
portions of Central Indiana remain drier through at least early to
mid afternoon with a lesser threat of strong storms later.

&&

.SHORT TERM (Today and tonight)...
Issued at 257 AM EDT Tue Jun 4 2024

Early this morning remnant cirrus and some mid-deck clouds were
approaching the far Southwest Indiana counties, while further
upstream a large area of cloud cover was nearly stationary. Despite
the lack of cloud cover, winds remain elevated in the 1-3km layer,
helping to produce some friction in the boundary layer and inhibit
the ability for the surface to easily decouple. Expect temps to
slowly radiate into mid 60s but could take until just prior to dawn
for this to occur.

After sunrise expect the upstream cirrus from overnight convection
to be arriving from the southwest. With cirrus overhead, expect the
depth to the mixing layer to be likely remain within the first
couple thousand feet of the surface. This should keep the boundary
from seeing any robust subsidence and maintain dewpoints in the
upper 50s to lower 60s. While there does appear to be some filtering
to the daytime heating, surface parcels should readily climb given
the slightly drier boundary layer conditions and change to heat
capacity. But if clouds become thicker earlier in the day this could
play a role in keeping temps in the lower 80s longer. Still appears
set that mid/upr 80s is in store for the afternoon, but with some
increased mid-lvl instability beginning to approach from the
west/southwest this could introduce additional cloud cover along
with an isolated showers/thunderstorm late in the afternoon.

Broad trough continues to slowly slide east, but appears for much of
the evening to remain displaced to the west. The southerly flow
moist layer will be advecting north across the Ohio Valley. Then the
question becomes when will precip overspread the area and what will
the precip footprint look like. Strong ascent to parcels upstream
this evening still looks to be probable, coupled with collision to
parcels as they steadily moisten and should help increase precip
shield late tonight. Guidance differs on coverage as well as timing,
so have not made many changes to the prior forecast of low chance
pops this evening, then increase in coverage and chances overnight.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 257 AM EDT Tue Jun 4 2024

Wednesday...

Main concern for the day will revolve around the convective
footprint and timing. The longwave pattern suggests a broad area of
southerly flow from the GOMEX streaming north through the Tenn
Valley into Ohio Valley. This allows the moist channel to stream
moist/ascending parcels through this area, continuing further
north/northwest with the low-lvl shortwave displaced across the
Upper Midwest. Upstream a 500mb trough will be sliding into the
Northern Plains, which should assist the ascending parcels further
in the downstream zones of the Ohio Valley. The question on whether
the surface will become unstable in the morning hours remains, but
the setup would suggest cloud cover shielding much of the solar
energy thus helping to limit how unstable the atmosphere becomes.

There does appear to be some organized convection developing
upstream early in the day and would further reinforce the northern
stream of cloud cover and eventual precip into Central Indiana by
midday/afternoon, but it is conceivable that some of this could get
more organized around daybreak. The trough axis will quickly pivot
east through Indiana in the afternoon, which should also push the
deeper layered moisture to the east along with convective elements.
But overall with lengthy ascent to already moist parcels what precip
that does fall will likely be from better collision coalescence of
parcels, coupled with the higher water content to the atmosphere and
any precip could easily produce more efficient downpours or pockets
of heavier rainfall.

Guidance has continued a progressive approach to the moist channel
steadily pushing east by the evening hours. It appears a secondary
trailing moist boundary will lag late Wed across the Western Great
Lakes stretching southwest through Iowa, and should push through
during the nocturnal hours. But there has been good agreement that
mid-lvl heights are leaning towards some weak diffluent flow which
should be enough subsidence to erode any lagging moisture. So feel
confident that precip will be done in the evening hours, then a dry
overnight progged for Indiana.

Thursday through Sunday... Generally the several days following Wed
appear primed to be incredible. Northwest flow will be the main
player, ushering in much cooler air to the region. Thur/Fri will
observe a pleasant thermal trough digging south that should help
keep afternoon temps in the 70s and overnight lows in the 50s. Sat
could feature enough mid-lvl moisture that some diurnally induced
sprinkles may develop. The steep lapse rates and perhaps some
surface destabilization during the afternoon could aid in an isolated
thunderstorm as well.

Sun guidance begins to deviate amongst ensembles members, as a
tropical remnant enters the far Southwest CONUS and appears to
introduce moisture to the southern Rockies. The deep trough should
be starting to relax marginally Sun, which likely will allow any
system to traverse the CONUS efficiently. While guidance is hinting
that a central CONUS precip footprint could develop, it would not
take much to introduce clouds and perhaps low chance precip to
Indiana by late Sun.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 108 PM EDT Tue Jun 4 2024

Impacts:

- Wind gusts to around 18KT out of the south, becoming westerly
tomorrow afternoon

- Scattered shower and storm after 20-23z continuing through
tomorrow afternoon.

- MVFR or worse conditions developing in showers and storms

Discussion:

Latest satellite and radar imagery shows an area of low pressure
moving NE into West Central Illinois with a boundary extending SE
into South Central Indiana. Showers and a few storms have already
been observed across far SW Indiana this afternoon. Expect
convection to increase in coverage from SW to NE through the
afternoon and evening hours. There will likely be a few rounds of
convection this evening and then again during portions of the late
evening and overnight hours. Expect cigs and vis to drop to MVFR or
worse under any convective activity this evening, then more
widespread MVFR cigs are likely to develop overnight and toward
sunrise. Potential is there for a break in convection sometime
during the morning hours Wednesday, before another line of showers
and storms develops and pushes east in the 15-20z timeframe
Wednesday. Confidence on exact timing of storms is low due to the
scattered nature of the storms and how dependent storm development
is on small mesoscale features which may not have formed yet. Higher
confidence exists in storm chances during peak heating of the day
later this evening.

Low level mixing and a tightening southerly gradient will result in
gusts of 15-20 kts this afternoon and evening. Winds will likely
remain elevated in the 8-12kt range overnight with higher gusts
under any convection.

&&

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

$$

UPDATE...CM
SHORT TERM...Beach
LONG TERM...Beach
AVIATION...CM