430
FXUS63 KIND 260404
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1204 AM EDT Sun May 26 2024

.KEY MESSAGES...

- Dry and Mild Tonight
- Storms arrive on Sunday, mid-morning through mid-afternoon.
- Severe Thunderstorms storms will be likely Sunday; Tornadoes
possible

&&

.FORECAST UPDATE...
Issued at 915 PM EDT Sat May 25 2024

Surface high pressure, over Lake Michigan, along with a flat ridge
and dry column has lead to clear skies across central Indiana this
evening. Good confidence that it will remain dry overnight as well
with only perhaps some increase in high cloud debris from the
approaching Plains convection. Would not completely rule out fog
toward daybreak but an approaching upper trough will act to veer and
increase southeast winds overnight to 10 knots which should
discourage fog.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 213 PM EDT Sat May 25 2024

Synopsis:

Surface analysis early this afternoon shows strong high pressure in
place over western IL. Light but cool NW flow was in place across
Central Indiana. GOES16 shows some stratocu clouds across central
Indiana on the leading edge of the approaching high pressure system.
Clearing was building across northwest Indiana, pushing east. Water
vapor imagery shows an area of subsidence pushing across Indiana and
Illinois. Looking farther west, a moderate trough was found over the
inter-mountain west, with southwest flow and lift ahead of this
system over CO emerging into the high plains. Temperatures over
Central Indiana were in the mid to upper 70s with dew points in the
lower 60s, revealing relatively moist lower levels.

Tonight -

Models suggest the surface high pressure will push across Indiana
and reach the eastern Great Lakes overnight. Forecast soundings
across Indiana reveal a dry column through the night as weak
southerly flow on the backside of the high develops. A strong dry
layer looks to remain within the middle levels due to previous
subsidence. Thus mostly clear but mild weather will be expected
overnight. Look for lows in the upper 50s and lower 60s.

Meanwhile the trough to the west is expected to emerge over the
plains and generate a strong convective system, an MCS, and an
associated area of surface low pressure. These features are these
features are expected to propagate toward Central Indiana, but not
reach Indiana, setting the stage for storms on Sunday.

Sunday -

An active weather day will be expected.

High confidence for rain on Sunday.

Severe storms will be possible with damaging wind gusts, very heavy
rain, lightning and even an isolated tornado.

At 12Z a strong MCS is expected to be in place over IL, pushing east-
northeast within the moderate flow aloft. Models show the trough
axis pushing east to the plains with the left front nose of the
upper jet poised to push across Central Indiana through the day.
This will provide strong lift through the day. Furthermore a
favorable air mass will be in place ahead of the arriving MCS as
forecast soundings suggest over 1500 J/KG of CAPE by mid day and
favorable wind shear. Meanwhile within the lower levels, an
associated area of low pressure over the plains is expected to push
toward Wisconsin, allowing for a warm front to be pushed across
Central Indiana along with a warm and humid southwest flow. Dew
points are expected to rise into the mid to upper 60s. The MCS
should be arriving across Central Indiana at a time which is
typically the diurnal minimum for these type of systems. However as
discussed earlier, several elements favorable for continued
convection are expected. The HRRR suggests an area of showers and
storms from the MCS over the Wabash valley by 15Z, poised to push
across our area through 20Z-21Z. Thus will focus highest pops during
this time period.

The key to precise timing and strength will be development of the
system over the plains tonight along with the evolution of the
system as it pushes east overnight, so all eyes will be on that this
evening. Best forecasts on timing and strength will be more clear
overnight.

Overall, showers and storms will be expected on Sunday, with more
storms expected on Sunday night. Cloud cover should limit heating
and highs in the mid to upper 70s should be expected.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 213 PM EDT Sat May 25 2024

Sunday Night.

The second and likely more significant round of storms is expected
during the evening to early overnight hours Sunday into Sunday night
as storms initiate across Missouri during the afternoon and quickly
grow upscale into a mature MCS by 6-7PM. Details on the broader
system associated with this severe weather is above.  Models have
come into much closer alignment in the timing and track of this
mature MCS with highest confidence in impacts after 6PM towards
12AM. The majority of the impacts with this system will likely be
seen south of the I-74 corridor with the highest threat for
tornadoes across the far southwestern portions of the forecast area
if not further south towards the Ohio River.

Any tornado that forms would be of the lower end QLCS variety with
little risk of thunderstorms outside of the main complex of storms.
Depending on the maturity of the cold pool, significant wind gusts
in excess of 70 mph look probable in at least portions of Indiana.
This will be a progressive system with storms exiting shortly after
midnight and only small chances for scattered light rain on the
stratiform portion of the backside of the system.

Flooding may be a concern depending on the amount of rain from the
initial wave of thunderstorms during the afternoon, but the
progressive nature of this system should keep total amounts less
than 1.5 inches.

Monday Through Thursday.

There may be some wrap around light rain showers Monday into Tuesday
as the parent upper level low sits across the Great Lakes region and
a strong northwesterly jet pivots around the low. Outside of any
rain, there should be fairly frequent and widespread cloud cover
through early Tuesday with cooler than normal temperatures. A weaker
secondary low within the broader upper level jet is expected to move
across the northern portions of the forecast area Tuesday night into
early Wednesday with a period of light rain likely. High pressure
then looks to set in with gradually warming temperatures through
Thursday.

Friday and Saturday.

The pattern will begin to shift Friday into Saturday as the ridge
of high pressure begins to break down and the next system exits the
Rockies. There is a wide spread in model guidance on the strength of
this low pressure system, but there is at least good agreement in a
cold frontal passage during the weekend with rain likely and the
severe potential being dependent on the more intense low pressure
system scenario panning out but even that looks very unlikely at
this time.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1203 AM EDT Sun May 26 2024

Impacts:

- Low probability of MVFR stratus early-mid morning

- First round of storms 15-20z; second round 00-05z

- Southwest winds will gust to 25 knots Sunday; higher near storms

Discussion:

Winds will veer from northeasterly to southeasterly this morning and
increase in response to an upstream weather system. There are
uncertainties with timing of thunderstorms associated with this
system and some adjustments to TAFs via amendments can be expected,
but the current thinking is 15-16z onset for most TAF sites for
round 1. Round 2 would occur around 00z or after. Both rounds have
the capability of producing strong wind gusts higher than the
already elevated gradient winds expected.

&&

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

$$

UPDATE...MK
SHORT TERM...Puma
LONG TERM...White
AVIATION...BRB