158
FXUS63 KIND 120730
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
330 AM EDT Mon May 12 2025

.KEY MESSAGES...

- Scattered showers this morning with thunderstorms possible in the
  afternoon. Severe weather is not anticipated.

- Periodic shower and thunderstorm chances expected much of this
  week...risk of strong/severe storms late Thursday

- Warmest air of the year so far expected for the late workweek...with
  record highs possible Thursday-Thursday night

&&

.SHORT TERM (Today and tonight)...
Issued at 328 AM EDT Mon May 12 2025

A large mid/upper-level low is lifting northward out of the lower
Mississippi Valley. The system is largely cut off from the polar
jet, which resides well to our north over the US Canada border. With
such weak steering flow, the system will move quite slowly and be
the region for a could of days this week.

Rich low-level moisture is advecting northward ahead of the
approaching system. The low-humidity weather we`ve seen for the past
few days will soon be a thing of the past as dew points steadily
rise into the 60s today. The muggy air mass then persists through at
least Thursday. Thankfully, abundant cloud cover and occasional rain
showers should prevent temperatures and heat indices from becoming
too high. Highs today should climb into the low to mid 70s.

Speaking of rain showers, showers should arrive as early as sunrise
this morning. Surface forcing is quite weak, so activity looks to be
scattered in nature and fairly weak given minimal convective
instability. Instability is weak, to start, but guidance shows CAPE
increasing to about 1500 J/Kg by the afternoon. As such, some
thunderstorms may develop as the day progresses. Model soundings
show fairly uniform flow through the column resulting in minimal
effective shear (under 20kt). Storms may be pulse-like or congeal
into loosely organized clusters. Severe potential is low.

Surface heating is lost at sunset and convective instability should
wane, leading to any residual showers or storms dissipating during
the night. A few isolated showers may persist but these will be far
and few between. Overall, the night will be mild with thick low-
level clouds hanging around. Lows should drop only into the 60s.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 328 AM EDT Mon May 12 2025

Tuesday and Wednesday...

The decaying yet broad upper trough will continue to slowly track
its western portions over Indiana...as its center spins from near
Tennessee early Tuesday to around Lake Erie by late Wednesday.
Overall resultant conditions for the local region will be above
normal warmth and humidity as light southerly breezes maintain
dewpoints in the low 60s...while providing afternoon highs in the
upper 70s to lower 80s.

Diurnally driven rain showers and a few non-severe thunderstorms
will be most pronounced Tuesday afternoon...when the weak steering
will allow locally heavier rain rates to possible promote isolated,
at least moderate rainfall over the region`s southern third where a
marginal risk of Excessive Rainfall is present.  Lesser chances of
widely scattered downpours on Wednesday with the axis of forcing
drifting across Ohio, yet a non-zero chance of excessive rainfall
should exist for eastern/northeastern zones.  Can not rule out
ponding of low-lying areas either day if caught under a stronger
shower/long-lasting t-storm, but flash flooding is not expected.
Most locations can expect a couple passing showers...outside of the
Tuesday afternoon timeframe which should feature numerous,
occasionally moderate showers.

Thursday through Sunday...

A taste of summer will be in store for the Midwest on at least
Thursday when this week`s warm trend reaches its peak...courtesy of
cyclogenesis over Minnesota coupling with an upper subtropical ridge
building northward into at least the Ohio Valley...boosting readings
to near-record levels in likely the upper 80s along with dewpoints
approaching 70F.  At least the southerly flow bringing this Gulf
juice will be on robust gusts around 15-25 mph which will provide
some relief to the tropical air.

A conditional strong/severe storm threat is on the table for late
Thursday into Thursday night as the relatively high theta-E boundary
layer air will produce high instability relative to the decreasing
mid-level heights amid the approaching northern system...along with
ample vertical wind shear arriving from the west.  Big question is
if the capped thermal profile can be overcome...which may be
determined by subtle changes in forcing aloft.  SHould convection
get going, a few severe storms could be possible especially during
the late day hours.  Details here will be refined through further
updates this week.

A more zonal upper pattern this weekend will follow the occluded
system lingering near Ontario.  Overall flat flow amid the rather
weak cool frontal zone that should drag/stall near the CWA, under
H500 heights near/above 570 dm...will promote more reasonable above
normal warmth, perhaps following one more warmer day in the 80s
Friday.  Chances for occasional convection should linger through the
long term`s final three days, especially around the late Friday/
early Saturday timeframe should a less-organized disturbance try to
scoot from the southern Plains to the Ohio Valley.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 146 AM EDT Mon May 12 2025

Impacts:

- MVFR ceilings much of the day Monday for most sites

- Scattered showers move north Monday morning. Isolated thunder
  possible mainly Monday afternoon. Rain chances diminish around 00z.

- MVFR/IFR ceilings possible tonight.

Discussion:

An upper level low will move north overnight into Monday, bringing
lowering ceilings and scattered showers and isolated storms.

VFR conditions are expected through the night, with MVFR ceilings
spreading south to north after 12Z. These will then mix out late
Monday afternoon into early evening.

Scattered showers will move north into the area mainly after 12Z.
Isolated thunderstorms will develop with instability in the
afternoon. Some uncertainty remains on just how much coverage of
rain there will be though.

Rain chances diminish this evening around 00z, though an isolated
shower is still possible afterwards. Guidance is hinting at MVFR/IFR
ceilings developing overnight, though based on observations further
south this may be a bit pessimistic. Will not explicitly forecast
IFR for now but trends upstream will need to be monitored closely.

Winds generally retain an easterly component early becoming
southeasterly later this morning. A few gusts up to 20kt are
possible during the afternoon hours.

&&

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

$$

SHORT TERM...Eckhoff
LONG TERM...AGM
AVIATION...50/Eckhoff