432
FXUS63 KIND 181915
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
315 PM EDT Fri Apr 18 2025

.KEY MESSAGES...

- Scattered severe storms with heavy rain and localized flash
  flooding late this evening through early Saturday morning

- Multiple rounds of rain continue into the weekend with the
  potential for the return of minor river flooding

- Peak wind gusts to 40 mph through early this evening

&&

.SHORT TERM (This evening through Saturday)...
Issued at 315 PM EDT Fri Apr 18 2025

Warm and windy afternoon in progress as temperatures have soared to
around 80 as of 18Z. The region has enjoyed plenty of sunshine so
far today but cloud coverage is increasing into the Wabash Valley as
a cold front tracks into the Missouri and mid Mississippi Valleys.

After the warm weather of today...the aforementioned cold front will
drift into the region late tonight as low pressure moves into the
Great Lakes. The boundary will become increasingly parallel to the
upper level flow eventually stalling near the Ohio River on Saturday
as further forward progress is blocked by the upper ridge over the
southeast states. The result will be a transition back to a wetter
and more active regime commencing later this evening with multiple
waves of convection impacting the forecast area into the overnight
and Saturday morning. Periodic showers will then continue through
the day Saturday as the front stalls.

Rest of This Afternoon through Mid Evening

Quiet weather continues through sunset across central Indiana. Wind
gusts peaking around 40mph will continue into the early evening with
the well mixed boundary layer. Could see temps bump up another
degree or two from current readings which could make for the warmest
day of the year so far for much of the forecast area.

Cannot rule out a few showers slipping into the Wabash Valley this
evening prior to 02-03Z...but a stout mid level cap noted off the
12Z ILX sounding and the current ACARS sounding from KIND will shut
down any convective impacts over the region for the next several
hours. The arrival and expansion of a low level jet over the next
few hours will help to break that cap across the mid Mississippi
Valley with convection developing to our west over Missouri and
Illinois between 22 and 01Z. As the jet noses into the region this
evening...the cap will weaken and largely diminish by late evening.

Mid Evening through Saturday Morning

The primary focus for severe weather and localized flash flooding
will come late evening into early Saturday morning as multiple
rounds of convection traverse the forecast area. While some
questions still remain with respect to convective evolution...the
overall model suite has trended in the direction of a primary
convective cluster late evening into the early overnight potentially
impacting the northwest half of the forecast area...followed by a
gradual shift south to heaviest storms overnight and into the early
part of the morning as the front sags into the forecast area.

The initial convective cluster set to track into north central
Indiana in the 03-06Z window will carry the greatest threat for
severe storms as MLCAPE values will be at their highest and aligned
with an increase in 0-1km SRH and shear values that will be well
above threshold levels and support storms in supercellular form.
While the damaging winds remain the primary risk with the strong low
level jet over the area...the potential for a tornado or two is
there with right turning hodographs developing within the lowest
1km. What likely keeps that threat from being greater is the hint of
a veer-back-veer (VBV) setup on model soundings late this evening
into the overnight. MOdest instability within the hail growth zone
will support large hail within the most intense cores as well.

The severe risk becomes murkier after 06Z as additional convection
develops to the W/SW ahead of the front with the focus shifting to
localized flash flooding from training convection. There remains
ample amounts of low level SRH and shear along with an LLJ peaking
near 60kts that would support potential for additional severe
weather most likely in the form of damaging winds...but MLCAPE will
slowly diminish into the predawn hours with an overall less
favorable thermodynamic profile. A much deeper influx of moisture
ahead of the slowing front will develop as PWAT values surge above
1.5 inches. The orientation of the jet from the W/SW as the night
progresses brings it more parallel to the front and ultimately
increases concern for convective clusters training as they move E/NE
across the forecast area. Greatest potential for locally heavy
rainfall appears to line up near the I-70 corridor after 06Z and
continuing through near daybreak before shifting into south central
Indiana.

Rainfall amounts by Saturday morning will be upwards of an inch but
where storms can train...amounts over 2 inches are in play and
support the potential for localized flash flooding during the
predawn hours and into Saturday morning.

Saturday Afternoon

The strongest 850mb winds will shift south to near the Ohio River as
the morning progresses which should aid in nudging convection
further south and diminishing rainfall coverage and rates into the
afternoon. Showers will remain across the forecast area...focused
especially across all but far northern counties with plentiful lift
near and north of the boundary and within a baroclinic zone.

Temps...the arrival of the front into the region towards daybreak
will enable temperatures to slip back into the mid and upper 50s
over the northern Wabash Valley with temps remaining above 60
elsewhere. Expect a modest temperatures gradient on Saturday with
the front settling over southern Indiana. Highs only in the low 60s
over northern counties will rise into the low and mid 70s over south
central Indiana. Any adjustment in frontal boundary location would
lead to changes in potential highs.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 315 PM EDT Fri Apr 18 2025

The long term period will start off with continued chances for
showers and thunderstorms as a stalled upper boundary continues to
sit over the region. An upper short wave and associated low will
track across the area Sunday into Monday, along the upper
boundary/leading edge of the bigger trough. This will allow for a
chance of storms throughout Sunday, especially for the early morning
to morning hours as the warm front pushes northward. There will
likely then be a break later in the day with highs warming into the
70s for central and southern parts of the forecast area, before the
associated cold front, and storms along the front, move through
Sunday night into Monday. Flooding will be the main concern for the
end of the weekend from persist rain

High pressure will then move in behind that system to allow for some
quiet weather though at least midweek. Past midweek, model
solutions become more varied and it is unclear exactly how the
forecast will pan out. There is some agreement on another low or
two passing through the area at some time late week, so have
slight PoPs persisting for that time frame.

Temperatures will be warmer than normal through the long term with
highs generally in the upper 60s to 70s and lows in the 40s to 50s.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1251 PM EDT Fri Apr 18 2025

Impacts:

- Southwest wind gusts peaking at 30-35kts through late day
- Gusts continuing tonight
- Periodic convection developing after 03Z and continuing into early
  Saturday morning
- MVFR conditions with showers Saturday

Discussion:

Deep boundary layer mixing and a tight surface pressure gradient
were contributing to southwest sustained winds routinely over 20kts
with gusts peaking at 30 to 35kts. This will continue for much of
the rest of the day even as diurnal cu develops and high level cloud
cover increases from the west. Winds will drop back this evening but
remain gusty.

The arrival of a cold front from the west will bring rounds of
convection impacting KLAF first late this evening then gradually
impacting the other terminals overnight as the boundary sags into
the region. Within heavier convection...brief IFR restrictions
and stronger wind gusts are possible late tonight.

The cold front will settle over the southern half of central Indiana
on Saturday with periodic showers continuing and widespread MVFR
conditions developing. Wind gusts will diminish during the predawn
hours to around 10kts Saturday morning. Winds will veer to northwest
at KLAF further north of the warm front with W/SW winds at the other
terminals.


&&

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

$$

SHORT TERM...Ryan
LONG TERM...KF
AVIATION...Ryan