160
FXUS63 KIND 081744
AFDIND

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

.KEY MESSAGES...

- Severe storms possible today, especially during the late afternoon
  and evening. Hail and wind are the primary threats.

- Heavy rain is possible at times through Wednesday night. Localized
  flooding will also be possible.

- 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.

&&

.FORECAST UPDATE...
Issued at 1004 AM EDT Wed May 8 2024

Watching the forecast closely today as another round of severe
weather is expected later this evening and tonight. While the worst
of the severe weather is forecast to be south of the Ohio River,
there still is a severe threat for much of Central and Southern
Indiana.

Latest surface analysis depicts an area of low pressure over western
Kansas with a warm front extending eastward through Missouri and
then along the KY/TN border where storms are currently developing.
Despite being north of the warm front, low level inversion overnight
kept the boundary layer fairly saturated with dew points remaining
in the 60s into this morning. Subsidence under ridging ahead the
approaching system to the west has resulted in clear skies this
morning for all of Central Indiana. Latest ACARS sounding from IND
does show a very dry column aloft, so once boundary layer heating
and mixing begin, expect drier air aloft to mix down to the surface,
lowering dew points back into the 50s, with the driest conditions
expect north of I-70. Will be watching the northward progression of
the warm front closely today as this may be the focus for storms to
develop and move eastward along later this afternoon and evening. A
concern is that widespread convection across KY/TN this morning may
inhibit the northward movement of the front some, keeping the main
focus for storms further south. Confidence on how far north the warm
front makes it is lower than what is preferred for being the day of
the event. Higher confidence does exist in that boundary making it
into Southern Indiana later today, where a more moist, and unstable
environment will develop with the best potential for severe storms.

Currently watching a complex of storms in Central Missouri
developing and pushing eastward, just north of the main warm front
and along an MUCAPE and Theta-E gradient. Expect additional storms
to form with this cluster through the rest of the morning hours.
These storms will likely continue to push eastward or southeastward
along instability/moisture gradients. That is why tracking these
sharp boundaries and fronts are so important for determining where
the severe threat will be later today. If these boundaries remain
south, then the storms will likely remain south along the
boundaries. Inversely, if these boundaries shift northward into
Southern Indiana, which is what short term guidance suggests, then
some severe storms will be likely in that region. Main forecast
challenge will be tracking these boundaries and highlighting which
areas/counties will be at the greatest risk for storms and which
areas will escape most of the threats. Higher confidence does exist
in a lower threat north of the I-70 corridor in North Central
Indiana.

&&

.SHORT TERM (Today and tonight)...
Issued at 303 AM EDT Wed May 8 2024

Synoptic Overview:

Central Indiana is now on the cool side of a warm front, which will
likely end up somewhere along a Kansas City to Paducah line later
this morning. For now, this frontal boundary is over southern IN,
and has suppressed surface winds, keeping a large portion of central
Indiana under light and variable conditions. On a separate, non
thunderstorm related note, these light winds in combination with
elevated surface moisture from prior rainfall will likely result in
patchy, dense ground fog over this area. As daybreak occurs, surface
heating should quickly mix out any fog, with 10mi or greater
visibility by 9AM.

For most of the day, central Indiana will be positioned within a
weak low level ridge, but also within strong upstream forcing and
moisture return. This ridge will act to suppress warm frontal
progression some, but high amounts of theta-e advection will
counteract this eventually lifting the warm front into central
Indiana. All CAMs have the warm front lifting northward throughout
the day, but even just 12-18 hours out, there is still significant
variability in placement. Generally, this frontal boundary is
expected to reach a Sullivan to Bloomington to Columbus line. This
is important as a majority of convective initiation is expected to
occur south of the front.

The aforementioned ridge will still have some influence on the
environment, keeping low level winds marginal and drying out the
near surface layer north of the front. Still, the impacts of the
upper level trough will allow for steep mid level lapse rates deep
instability profiles across much of the region. Theta-e advection
within the warm sector will also act as a lifting mechanism helping
establish CI later this afternoon.

Severe Weather Hazards and Timing:

As stated, CI is expected to occur continuously this evening south
of the warm front once convective temperatures are reached. There
will also be a convective threat overnight, but that will be highly
depending on the location of MCS development.

For today, the wind profile will look 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 central 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).

The overnight threat will be primarily due to any MCS that
potentially forms west of central Indiana. This is currently highly
uncertain, due to substantial model inconsistency. However, if an
MCS does pass through overnight, a high wind threat will be
possible.  Given the west to east placement of the warm front and
the resulting upshear vectors, training thunderstorms will be
possible in this overnight regime. Because of this localized
flooding will be possible.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 303 AM EDT Wed May 8 2024

Thursday through Saturday...

A pair of upper waves and associated cold fronts in northwest flow
aloft will dive southeast across central Indiana and bring more
convection to mainly northeastern sections Thursday and again
Friday night and Saturday. Model agreement is good on the handling
of these features.

Temperatures will be noticeably cooler, especially Friday and
Saturday with below normal highs in the 60s.

Saturday night and Sunday...

Weak ridging and a fairly dry column will lead tranquil weather late
in the weekend along with temperatures moderating back to near
normal Sunday with afternoon highs in the upper 60s to middle 70s.

Sunday night through Wednesday...

Confidence is low on PoPs and temperatures next week as models agree
that split flow will develop over the Plains and a broad trough will
eventually move through the Ohio Valley. The question is when as
models and their ensembles are having trouble coming together with
big timing spreads. With these differences, did not make any changes
and left small convection chances in through the period along with a
warming trend due to the winds shifting to a southerly component.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 144 PM EDT Wed May 8 2024

Impacts:

- Severe weather threat shifting south of Central Indiana

- Expect showers and sub-severe storms pushing in this evening

- Potential for MVFR cigs late tonight


Discussion:

As with a lot of large severe weather events, things can change
rapidly depending on where boundaries set up and other smaller
mesoscale details. Latest indications are that the main severe
weather threat will be south of Central Indiana TAF sites this
evening and tonight.

With that said, latest satellite and radar imagery show a cluster of
storms in Missouri and Southern Illinois along a warm front. Latest
guidance does indicate this warm front remaining south of the TAF
sites, keeping the main severe weather threat south. However, sub-
severe storms and showers are still possible later this evening at
KHUF and KBMG. Lower confidence exists if KIND will even see
lightning with showers later on this evening. Currently, timing for
any convection in the area looks to be around 23z to 05z, with
lingering isolated showers and MVFR cigs after that.

Winds have been light and variable much of the day remaining under 7
kts at most sites. As the main low pressure pushes near the region
tonight, expect winds to become southerly at all locations, then
becoming west-southwest during the day tomorrow increasing to 10-15
kts. Additional chances for showers and thunderstorms are possible
tomorrow morning into tomorrow afternoon; however confidence remains
low on coverage of convection and exact timing.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 6 PM EDT this evening through late tonight for
INZ056-064-065-071-072.

&&

$$

UPDATE...CM
SHORT TERM...Updike
LONG TERM...MK
AVIATION...CM