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FXUS63 KIND 062253
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
653 PM EDT Mon May 6 2024

.KEY MESSAGES...

- Scattered howers with a few thunderstorms through early evening

- Severe storms expected Tuesday especially during the afternoon and
  evening. All forms of severe hazards are possible.

- Additional severe storms are possible Wednesday afternoon and
  evening. All forms of severe hazards are again possible.

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

&&

.SHORT TERM (This Evening through Tuesday)...
Issued at 305 PM EDT Mon May 6 2024

Convection has become more scattered this afternoon while the
thicker clouds this morning have mixed out a bit and enabled some
sunshine to filter through. This has introduced a weakly unstable
environment over much of the area as low pressure passes by to the
south. 18Z temperatures were in the 70s.

While some time will be spent on the scattered convective potential
into the early evening...the primary focus for the short term will
be on the initial severe weather risk focused on Tuesday afternoon
and evening as a series of waves aloft kick out from a deep upper
level low that will position itself over the northern Plains on
Tuesday.

Rest of This Afternoon and Tonight

Weak surface wave near the Ohio River passing by just south of the
forecast area this afternoon. Despite the lull in precip coverage
referenced above over the last few hours...starting to note an
uptick in convection across southern counties currently...likely
being aided by the weak instability. Broader area of rainfall just
northeast of KSDF may pivot into the far southeast counties over the
next few hours before kicking out to the east of the region.

Will continue to see isolated to scattered convection into the early
evening as the low shifts into northeast Kentucky. The presence of
near 1000 j/kg CAPE values should be enough for a few rumbles of
thunder as well. Showers will diminish shortly after sunset with the
loss of heating and a stabilizing atmosphere. Have held onto low
pops through mid to late evening but then expect dry conditions
thereafter.

The rest of the overnight will see low clouds gradually increase
with a focus turning to the west as the elongated robust convective
line slated to develop over the central Plains later this afternoon
steadily approaches the region from the west overnight. A strong
50+kt low level jet will help drive that convective line all night
with the likelihood that the storms will be nearing the Wabash River
shortly after 12Z Tuesday in a weakening state.

Tuesday Convective Round #1

Convection will be in the process of outrunning the better low level
jet dynamics by daybreak and the jet will weaken even further during
the morning as the storm line arrives into western Indiana.
Depending on cold pool depth from the overnight storms...convection
is likely to be in a subsevere state by the time it arrives in
western counties Tuesday morning. While overall instability profiles
will be minimal across the forecast area in advance of the
storms...an axis of stronger storm relative helicity within the 0-
1km range to enable the convection to maintain some level of
intensity as it tracks across the forecast area through midday.

Storms are likely to have hail and gusty winds associated with them
but model soundings do hint at the remnant of a nocturnal inversion
which should mitigate some of the wind transport to the surface.
Even while the instability is weak as mentioned above...the CAPE
profile is skinny and throughout the depth of the column with
likely presence in the hail growth zone as well. To sum
up...storms Tuesday morning will disrupt outdoor activities with
brief heavy rainfall and lightning diminishing and at least some
potential for small hail and gusty winds. But overall...the severe
potential looks low through midday Tuesday.

Tuesday Convective Round #2

The remnants of the morning convective line will be moving away by
early afternoon...leaving behind the warm front which will surge
north into north central Indiana and potentially leftover outflow
boundaries from the morning activity. With strengthening southerly
flow and an approaching surface wave along an occluded
boundary...the airmass will quickly moisten and destabilize with a
rapid advection of theta-e into the region by mid afternoon. This
will set the stage for renewed convective development after 18Z over
Illinois and eventually migrating into central Indiana.

All signs are coming into form for severe weather from mid afternoon
into the evening. CAPE values will rise to above 2000 j/kg with BL
shear and 0-1 km SRH values remaining more than sufficient for
robust convection initiation and development through the second half
of the afternoon. Diffluent flow aloft on the lee side of the deep
upper low over the Dakotas and the passage of an upper level wave
through the region will further aid convective development and
expansion. Model soundings become quickly favorable for all forms of
severe weather with directional shear within the boundary layer
present along with large right-turning hodographs.

While all of the above is strongly supportive of severe convection
and supercell development as well...the eventual position of the
warm front will become the wild card and could serve as a focal
point for the best threat for severe and perhaps rotating storms
carrying a tornado risk as well. At this point...that appears most
likely to align across far northern portions of the forecast area
during the late afternoon. With the strongest SRH values setting up
just to the northeast of the region...expect the primary tornado
risk late day Tuesday will be across northeast counties. Other than
the tornado threat...large hail will be a big concern with an
abundance of instability and stronger winds aloft within the hail
growth zone. Stronger cores will also carry a damaging wind risk with
drier air aloft and a near dry adiabatic flow through the boundary
layer.

Have highlighted the severe risk through graphics and products
shared on our social media platforms. Storms will shift east of the
area by late evening Tuesday as the front pushes back south and weak
ridging reestablishes. This is a temporary break in the storms with
another round of severe weather slated for late Wednesday and
Wednesday evening as the frontal boundary surges back north. More on
this in the Long Term Discussion below.

Temps...expect lows into the upper 50s far north with 60s elsewhere
tonight. Low level thermals support highs in the upper 70s and low
80s for much of the area Tuesday with a noticed uptick in humidity
as well.

&&

.LONG TERM (Tuesday Night through Monday)...
Issued at 305 PM EDT Mon May 6 2024

Late Tuesday night through Wednesday night...

A break in convection is expected to start late Tuesday night, with
even weak ridging building into central Indiana from the subtropical
surface high pressure to our southeast.  Despite clearing skies,
lighter southwesterly breezes will hold dewpoints in the upper
50s...resulting in low temperatures around 60F across the region.

Wednesday will bring another favorable set-up for convection and
perhaps widespread severe weather with a warm frontal type boundary
likely slowly advancing northward near our southern counties ahead
of a strengthening surface low slowly approaching over the Middle
Mississippi Valley.  Much of the day Wednesday may be the quiet
before the storm as the narrow ridging between the two systems
continues to cross the CWA...albeit eventually self-destructive with
the bright skies bringing low 80s and light southerly winds holding
dewpoints in the 55-65F range.  Resultant CAPE by 21Z should range
from 1000-3000 J/kg from north-south...including moderately strong 7-
8 deg/km lapse rates over most of the area.  Widespread 40-55 kt 0-6
km shear will also support arriving/developing convection.

So far appears most likely storm pattern will be a mesoscale
convective system initiating in the afternoon somewhere in the
central/eastern Illinois region...before tracking eastward into
Indiana during the late day/early evening hours.  This would likely
transition into more of a heavy rain/flooding threat later in the
evening and into overnight hours, especially south of I-70 amid the
system`s warm sector`s anomalous precipitable water values
approaching 2.00 inches.  While the environment would support
discrete cells ahead of a later MCS arrival...organized severe
weather`s location would be dependent on warm frontal position, with
timing likely determined by where/when storms begin to fire to our
west.

All severe hazards are on the table for PM hours Wednesday with
damaging winds and large hail the greatest threats during the
afternoon/evening...and flooding the greatest concern for the
evening/overnight.  Although it is only early May, the set-up and
potential are perhaps more indicative of a June pattern with the
synoptic set-up able to effortlessly fuel ample deep moisture into
central and especially southern Indiana.  Rain chances will drop
from west to east late Wednesday night as the supporting surface low
crosses the state.  Total 24-hour rainfall potential for Wed-Wed
night will be 1.00-2.50 inches along/south of the I-70 corridor,
with less than 1.00 inch expected for most locations north of I-70.

Temperatures will be above normal amid the S/SW flow and overall
warm sector of the passing/approaching systems.  Expect low 80s
ahead of convection Wednesday...while lows Wednesday night amid
decreasing chances of rain ranging from the upper 50s near Lafayette
to the mid 60s south of the I-70 corridor.

Thursday through Monday...

The last five days of the long term will then trend to at least a
couple northern stream, positively-tilted short waves cycling from
the northern Plains into the Midwest.  Not the greatest certainty
with this pattern, with some guidance members originally hinting at
the second wave plunging and inducing a strong baroclinic
circulation near the Ohio Valley around the Sunday/Monday timeframe
...however, latest data now suggests amplification will be more
modest, which should keep the pattern more progressive over the
region thru the end of the long term.

This should translate to near to slightly below temperatures amid
west-northwesterly breezes.  Thursday will be marked by robust to
gusty breezes as the gradient from the combination of departing low
pressure and the passage mid-level supporting vort.  The 5-day
period will include several chances for at least stray showers under
the troughy flow...with more organized showers expected both
Thursday and Saturday per corresponding short waves.  Widespread
and/or heavy rainfall could be possible early next week should the
weekend wave plunge and phase, although currently low chances in
this set-up coming to fruition.  The normal max/min at Indianapolis
through the long term is 72/52.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 652 PM EDT Mon May 6 2024

Impacts:

- MVFR conditions developing overnight and persisting into Tuesday
  morning. Potential for IFR.

- Line of convection will move through on Tuesday morning

- Winds become south and gusty on Tuesday

Discussion:

Isolated showers near some TAF sites will diminish early. With
lingering low level moisture, MVFR conditions will develop
overnight. There is a potential for IFR conditions in stratus in fog
late tonight, but for now confidence is not high enough to include.

A line of convection will move east into the area around 13Z and
will march east across the sites. MVFR conditions and worse are
possible in that. Improvement will occur by Tuesday afternoon, but
additional convection may develop.

&&

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

$$

SHORT TERM...Ryan
LONG TERM...AGM
AVIATION...50