539
FXUS63 KIND 082340
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
740 PM EDT Wed May 8 2024

.KEY MESSAGES...

- Diminishing severe weather threat. Main threat will be to the far
SW and S Central Indiana.

- Heavy rain is possible at times through through tonight across
the far southeast.

- Periodic chances for showers and a few storms late week into early
next week.

- Normal to slightly below normal temperatures Thursday through
Saturday with warmer temperatures next week.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 307 PM EDT Wed May 8 2024

Quite a few changes made to the forecast for the rest of the evening
with this afternoon`s forecast package as the severe weather threat
across much of Central Indiana has diminished. Still watching far
southwest and southern Indiana for severe weather potential tonight;
however the threat significantly diminishes northward into Central
Indiana.

For most of the day, Central Indiana has been positioned within a
weak low level ridge, but also within strong upstream forcing and
moisture return. The ridge overhead and numerous convective activity
along the front has kept it from surging northward into Indiana as
guidance previously suggested over the past few days. Strong daytime
heating of the boundary layer has resulted in temperatures rising
into the 70s and low 80s in Central Indiana; however deep mixing has
brought down significantly drier air to the surface. Latest IND
ACARs sounding continues to show significant dry air through the
column with mixing heights over 1 km agl. Observations at KIND have
reported dew points falling into the mid to upper 40s at times this
afternoon creating a strong north to south dew point gradient across
the state with dew points ranging from the the 40s north of I-70 to
mid 60s in South Central and SW Indiana. Satellite imagery clearly
depicts a strong instability gradient south of the region with
billowing cumulus clouds from Central Missouri to Southern Illinois
and across Southern Kentucky. North of that instability gradient,
strong low level capping, observed on the Louisville ACARs sounding,
has prevented cu development, even in areas in South Central Indiana
with better moisture return and higher dew points. Once that cap
breaks, short term hi-re models do show convection developing along
and south of this dew point gradient in far SW and South Central
Indiana. Confidence is increasing that the severe weather threat
will likely stay along and south of this line from around Sullivan
Co IN to Columbus to Greensburg, IN. Even then, confidence is low in
severe weather making it much further north than the Ohio River, but
this will be something closely monitored over the next few hours.
Confidence is also increasing that areas north of that line,
including the I-70 corridor and Indy Metro area and points north
will likely escape the severe weather this evening and tonight.

For areas that do see pop up convection this evening, main severe
weather threats will be damaging winds, large hail, and possible
flooding in areas the received high rainfall amounts yesterday.
Timing for potential severe weather is around 4pm to 9pm.

As far as the atmospheric set up, the discussion from this morning
sums it up very well. The wind profile looks much differently than
yesterday, with winds in the lower 3km much weaker due to the
aforementioned ridge. However, winds aloft will remain rather robust
with a westerly 500mb to 300mb jet placed direction aloft. This will
likely lead to a variety of storm modes including multicell clusters
and lines as well as a few supercells. Any supercells that due
develop will have the tendency to split.

Within the initial evening threat. Tornadoes look unlikely given the
lack of low level winds, and high LCLs, but a strongly deviant right
movers in far southern central Indiana where dew points are elevated
could have enough streamwise vorticity ingestion for isolated
tornadoes. Hail and wind on the other hand will pose the main threat
for Southern and SW Indiana. Deep CAPE profiles with strong flow
through the Hail Growth Zone will promote a large hail threat, and
dry mid-level air and DCAPE values over 1000J/kg should create a
environment capable of efficient downward momentum transfer and a
damaging wind threat. These threats will be greatest in any
supercells that form (especially hail within left movers).

There is a flooding threat across portions of SE Indiana where 1.5
to 3 inches of rain fell from yesterdays storms. There is a Flood
Watch out for the SE Indiana counties from 6PM to 3AM as any heavy
rain from potential storms will easily be able to cause flooding on
local streams and low lying areas.

.Tonight...

As mentioned above, the main warm front and instability/moisture
gradients continue to remain further south than what previous
guidance has depicted. Today`s guidance has picked up on that trend
and keeps any overnight convection along these boundaries, keeping
much of Central and North Central Indiana drier. Rainfall under the
anvil of a developing convective complex along the front will likely
make it into Central Indiana later this evening and tonight, but
amounts will be very light.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 307 PM EDT Wed May 8 2024

Numerous upper waves will be moving through during the long term
period bringing multiple chances for showers and thunderstorms,
especially for the latter half of the period. Temperatures will
start out slightly below to near normal and warm back to above
normal for next week.

Friday will start off with the first upper wave passing overhead but
there doesn`t appear to be much moisture with it. While a few
isolated sprinkles can`t be ruled out, it appears more likely that
conditions will remain largely dry enough Friday to keep PoPs near
10% per guidance. The next wave will bring a better chance of precip
as the associated surface low tracks across the Great Lakes Friday
through Saturday. This wave has led to PoPs for much of central
Indiana from Friday night through Saturday. Multiple models
currently have the showers and possible thunderstorms moving off to
the east by mid to late Saturday morning but another model is slower
to move the precip out. While exact timing is not quite narrowed
down, there is a consensus of minimal rainfall amounts expected with
this system. Outside of the rain, Saturday will also be breezy with
gusts up to 35 mph possible.

A surface high is then expected to progress just to the south of the
forecast area allowing for quiet weather Sunday and the start of a
warming trend for the new week. Models then vary and become noisy
with their solutions for next week leading to less confidence in at
least the precipitation forecast. There is general agreement in a
troughing system moving in with overall westerly to southwesterly
upper flow ahead of it but timing and strength of the trough is
unclear at this time. Going to keep with slight to chance PoPs over
several days that guidance provided.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 740 PM EDT Wed May 8 2024

Impacts:

- SHRA and a few sub-severe t-storms this evening
- CIGs deteriorating to MVFR late this evening

Discussion:

Organized thunderstorms/severe threat will continue to remain to the
south of central Indiana this evening along the Ohio Valley/Kentucky.
However, scattered to numerous showers with embedded thunder and
isolated stronger gusts are possible near terminals, especially at
KHUF/KBMG through 06z.  Ceilings are expected to deteriorate quickly
to MVFR/possible IFR late this evening from southwest to northeast...
with MVFR maintained through Thursday morning.

Notably light surface flow will increase/back slightly to southerly
this evening, with sustained winds of 7-10KT expected through the
late overnight across the region...with gusty conditions possible
in/near any stronger cells, although confidence is too low to include
in any TAF.  More pronounce veering Thursday morning will yield west
winds by 18Z, with increasing winds gusting up to 20-25KT in the
afternoon. Scattered showers/storms are possible Thursday, with
lower certainty regarding coverage/timing of any convection.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 3 AM EDT Thursday for INZ056-064-065-071-072.

&&

$$

SHORT TERM...CM
LONG TERM...KF
AVIATION...AGM