IND issues Area Forecast Discussion (AFD) at Sep 12, 2:09 AM EDT366
FXUS63 KIND 120609
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
209 AM EDT Sat Sep 12 2026
.KEY MESSAGES...
- Showers and embedded thunderstorms early this morning, especially
across the southeast half of central Indiana
- Additional isolated to scattered storms this afternoon
- Scattered storms Sunday afternoon and evening
- Heat returning Tuesday and Wednesday
&&
.DISCUSSION (Today through Friday)...
Issued at 209 AM EDT Sat Sep 12 2026
An upper level wave will bring scattered showers and embedded
thunderstorms this morning focused mainly across the southeast half
of central Indiana. Additional isolated storms are possible this
afternoon before weak high pressure builds in tonight. After a brief
cooldown Monday...upper ridging will expand north into the region
through the middle of next week with hot temperatures returning. A
cold front will become nearly stationary across the lower Great
Lakes before gradually sliding into the Ohio Valley during the
second half of next week with increasing chances for showers and
thunderstorms.
Today through Monday Night
Clouds were increasing from the southwest early this morning in
response to an approaching upper level wave. Convection has been
ongoing across the western Tennessee and lower Ohio Valleys since
Friday evening and had now advanced into the lower Wabash Valley.
06Z temperatures ranged from the mid 60s north to the mid 70s south.
The upper wave is the primary feature of interest in the near term
as it pivots across the region through this afternoon. An organized
area of convection will continue to track northeast across the
forecast area through daybreak. While storms have had a history of
stronger winds across far southwest Indiana...anticipate a gradual
decrease in intensity as it lifts northeast through the forecast
area with less instability present. The main concern from the storms
will be the potential for locally heavy rainfall as PWATS near 2
inches advect into the area and the airmass below 500mb is
exceptionally moist. High rainfall rates have already been noted
west of KEVV earlier and while a downtrend in convective intensity
should lead to diminishing rates...there are likely to be some
locations over the lower Wabash Valley and southern parts of the
forecast area that see a quick 1 to 2 inches of rain.
The weakening area of convection will move east of the region during
the first half of the morning with scattered lighter showers and an
expansion of lower stratus enveloping much of the forecast area
through midday. As the stratus mixes out into a cu field this
afternoon and heating commences...potential is there for isolated
convection developing across primarily the eastern half of the
forecast area on the back side of the departing upper wave. MUCAPE
levels increase to 1000-2000 j/kg with abundant moisture lingering.
The convection will shift east by early evening as the upper wave
moves away to the east.
Weak high pressure builds in tonight in the wake of the upper wave
with cloud coverage diminishing. Could again see patchy fog near
daybreak Sunday within the muggy airmass. Sunday will begin dry but
the approach of a cold front from the northwest will spread the risk
for scattered convection back into the forecast area for the
afternoon and evening. A surge of cooler and much drier air will
follow in the wake of the frontal passage Sunday night as a strong
high pressure builds into the upper Midwest. The high will pivot
across the Great Lakes on Monday with an axis of deep subsidence
swinging across the area. Return southerly flow will begin to draw
moisture back into the region as soon as Monday night with the high
shifting into New England. The upper ridge will also progress
towards the Ohio Valley setting the stage for a return to a hotter
regime for Tuesday and Wednesday.
Temps...Highs today will range from around 80 in eastern parts of
the forecast area where clouds and the threat for rain will last much
of the day...to the mid 80s in the Wabash Valley. Low level thermals
support highs in the low to mid 80s Sunday as well. With the Sunday
night frontal passage...MOnday temperatures will pleasant ranging
from the mid 70s in the northeast to the lower 80s in the Wabash
Valley.
Tuesday through Friday
Return southerly flow will develop on the back side of the departing
high quickly on Tuesday as mid level heights rise across the Ohio
Valley. Highs will likely warm back into the lower and possibly mid
90s Tuesday and Wednesday as the upper ridge centers over the
Tennessee Valley. With a frontal boundary stalled to the north over
the Great Lakes...convective risks will be isolated and diurnally
driven at best.
A retrogression of the ridge into the Southern Plains by late week
will finally enable the front to press south into the region with an
increasing threat for scattered convection across the forecast area.
The heat will be pushed back south as well with temperatures sliding
into the lower and mid 80s by Friday then into the upper 70s next
weekend. Extended model guidance has backed off on the arrival of a
much cooler airmass into the region perhaps not until the 10 to 14
day range as a more chaotic quasi-zonal flow aloft remains across
much of the northern half of the country by next weekend.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1235 AM EDT Sat Sep 12 2026
Impacts:
- Scattered to numerous showers with embedded thunder predawn hours
to near daybreak, especially at KBMG and KIND
- Patchy fog possible predawn hours
- MVFR ceilings developing through midday
- A few thunderstorms will develop mid to late afternoon
Discussion:
A convective cluster over the lower Ohio Valley will lift northeast
into the region over the next several hours. Should see lightning
strikes diminish from current levels as it lifts into southern
Indiana but still feel short TSRA tempo groups are warranted at KBMG
and KIND between 08Z and 11Z. MVFR ceilings will accompany the
showers and settle over all but KLAF around or shortly after
daybreak as the area of rain shifts away to the northeast. Patchy
fog may develop at KLAF in the predawn as well.
Lower clouds will linger into the early afternoon before lifting
into a broken VFR cu field. Enough instability will remain for
isolated convective development this afternoon on the back side of
the departing upper level wave...focused primarily over the eastern
half of central Indiana. Any rain threat will end by early evening
with skies clearing as weak high pressure builds in tonight.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
AVIATION...Ryan
DISCUSSION...Ryan
Source:
IND issues Area Forecast Discussion (AFD) at Sep 12, 2:09 AM EDT---------------
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