893
FXUS63 KIND 121738
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
138 PM EDT Sat Sep 12 2026

.KEY MESSAGES...

- Isolated to scattered storms through the evening

- Additional scattered storms Sunday afternoon and evening

- Heat returning Tuesday and Wednesday, highs in the low 90s

&&

.DISCUSSION (This evening through Saturday)...
Issued at 138 PM EDT Sat Sep 12 2026

Overview.

A cold front passing through Central Indiana tonight with rain
chances decreasing through the evening. This front won`t make much
of a difference in temperatures with highs climbing into the low to
mid 80s for Sunday. High pressure will keep conditions calm and mild
through early next week. Rain and thunderstorm chances return
Wednesday night into Thursday as another storm system approaches
from the west, followed by cooler air on Friday.

Tonight Through Sunday Night.

A broad upper-level trough over the Upper Midwest will pivot
eastward into the Great Lakes overnight, driving an attendant
surface cold front southeastward across Central Indiana between 03Z
and 10Z. HREF guidance shows a narrow plume of moisture transport
preceding the boundary, pushing PWAT values near 1.3 to 1.5 inches.
Despite limited elevated instability, moderate PVA aloft combined
with 30-35 kt of 850mb jet dynamics will support a organized band of
rain showers and embedded thunderstorms through the evening hours
with rain chances gradually dropping ahead of the frontal passage.
HREF ensemble members maintain peak MLCAPE values below 500 J/kg,
limiting severe convective potential, though brief heavy downpours
and wind gusts up to 30 kt remain possible with the strongest cells.

Post-frontal cold advection aloft will increase through Sunday
morning in the 925-850mb layer as the surface trough exits.
Deepening boundary layer mixing under steep low-level lapse rates
will allow momentum transfer down to the surface, resulting in
sustained northwest winds of 15 to 20 mph with gusts up to 25 to 30
mph. Lingering boundary layer moisture trapped beneath a 850mb
subsidence inversion will maintain a broken stratocumulus deck
through midday Sunday before large-scale anticyclonic flow and dry
air advection scour out remaining cloud cover. As surface high
pressure builds eastward into the middle Mississippi Valley Sunday
night, clearing skies and decoupling surface winds will foster
efficient radiational cooling, dropping low temperatures into the
upper 40s to lower 50s across the forecast area.

Monday Through Friday.

Surface high pressure centered over the Ohio Valley on Monday will
shift off the Mid-Atlantic coast by Tuesday. Mid-level height rises
across the Midwest under building ridge flow will maintain strong
broad-scale subsidence across Central Indiana. The combination of
dry atmospheric profiles and gentle southerly return flow on the
backside of the surface high will allow high temperatures to
moderate from the upper 70s to low 80s on Monday with much warmer
temperatures arriving Tuesday into Wednesday.

The synoptic pattern transitions to a more active configuration by
mid to late week. Both operational GFS and ECMWF, supported by their
respective GEFS and EPS ensemble means, depict a deep mid-level
trough ejecting out of the Southern Rockies into the Central Plains
on Wednesday. Strong warm advection and an intensifying 45 to 55 kt
850mb low-level jet will direct a surge of Gulf moisture northward
into the region, pushing PWAT values above 1.60 inches by Wednesday
night. Enhanced upper-level jet dynamics and increasing PVA ahead of
the advancing cold front will support widespread rain showers and
embedded thunder late Wednesday night into Thursday. While shear
profiles appear sufficient for organized convection, the overall
magnitude of instability will depend heavily on cloud cover and
diurnal timing. The cold front completes its passage by Friday
morning, returning the region to northwest flow aloft, post-frontal
CAA, and drier, cooler conditions heading into the weekend.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 138 PM EDT Sat Sep 12 2026

Impacts:

- Scattered showers at BMG and IND through the early evening
- MVFR to briefly IFR cigs through 00Z
- Areas of fog tonight, mainly after 08Z

Discussion:

Scattered showers with a low chance for thunder will continue
through around 21Z at IND and BMG before coverage drops low enough
to not warrant a mention in the TAF. Cigs have generally risen to
MVFR but can`t rule out brief IFR through 21Z. As skies clear during
the overnight hours and winds drop to near calm, areas of fog are
expected to form with the main question being how dense the fog will
be. Winds will generally remain southerly to southwesterly through
06Z at 5-10kts before becoming northwesterly at 2-5kts.

&&

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

$$

AVIATION...White
DISCUSSION...White