808
FXUS63 KIND 211918
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
318 PM EDT Fri Aug 21 2026

.KEY MESSAGES...

- Isolated/scattered showers and a few t-storms are possible late
  Friday night...and again Saturday afternoon, mainly east.

- Cooler and less humid weather expected Sunday through Tuesday with
  highs mainly in the 70s to near 80.

- Areas of late night/early morning fog will occur Saturday and
  Sunday nights.

- Dry weather expected Monday and Tuesday with increasing chances
  for rain and storms mid-late next week.

&&

.DISCUSSION (This evening through Friday)...
Issued at 318 PM EDT Fri Aug 21 2026

Late this Afternoon...

Elevated showers over northern Indiana are indicative of a weak lead
shortwave. An instability axis extends across far eastern portions
of the forecast area northward into NE Indiana. Recent convective
development in NE Indiana was occurring in a zone of modest low
level convergence. There is a small chance that an isolated shower
or TS will develop in extreme northeastern zones before activity
weakens around sunset.

Tonight and Saturday...

Vigorous convective development will continue to the northwest of
central Indiana across parts of southern WI/far northern IL and
eastern IA the remainder of the afternoon into the evening. This
activity is forming in a broad convergence zone ahead of a
seasonably strong shortwave trough and within a moderate to strong
instability axis with MLCAPE values from 2000-3000 J/KG. TS activity
in several lines will develop develop S-SE towards central Indiana
overnight. However, instability decreases markedly with SE extent,
with MUCAPE under 1000 J/KG across all of central Indiana overnight.
Time of day combined with minimal instability suggests that the
severe weather threat is close to zero across the forecast area.
Well south of any precip and/or convective clouds overnight, patchy
fog is expected across southern portions of central Indiana where
light winds and mostly clear skies will prevail.

The weak cold front associated with this progressive system will
push across the region Saturday morning. There is some indications
that a secondary shear induced mid level vorticity max will move
through the region on Saturday afternoon. With residual instability,
a few lower topped showers/TS will be possible behind the main cold
front but ahead of this mid level feature/surface convergence
boundary during the afternoon, mainly over eastern zones. Have
maintained pops in these regions. Would not be overly surprised
with some renegade showers across western zones where some
instability remains, but for the sake of consistency will leave
out of the forecast.

Saturday night through Sunday...

In the wake of the shortwave/cold front Saturday surface high
pressure will gradually build southward through the northern/central
plains into the upper MS valley. Broad NW low level flow will
support some lake enhanced clouds and showers Saturday evening and
again during Sunday afternoon in far northern areas mainly during
the period when daytime heating/convective overturning is
maximized. A stout mid level inversion noted on forecast
soundings should limit convective cloud depth and only a slight
chance of showers is currently forecast.

Sunday night through Tuesday...

Broad area of surface high pressure will push SE into the Ohio
Valley through the period, providing for much drier conditions, with
dewpts falling into the 50s. As a result most areas will see low
temperatures in the 50s Sunday night. Light winds and mostly clear
skies will lead to another night with areas of fog Sunday night. A
weak system in the NW flow aloft is expected to move across the
MO/mid-MS valleys Monday into Tuesday. At present the only
expected effect from this system will be increasing mid-high
clouds. This should limit fog chances Monday night and keep high
temperatures in the 70s most areas Monday and Tuesday.

Wednesday through Friday...

Another upper wave/surface cold front will move through during the
period. Confidence in timing is very low considering the system is
currently off the west coast, so for now will only have some low
PoPs. Seasonable temperatures are expected with increasing humidity
with increasing SW flow in the low levels.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 116 PM EDT Fri Aug 21 2026

Impacts:

- Isolated to scattered showers and storms late tonight into
  Saturday morning
- Low chance for brief fog at outlying sites Saturday morning

Discussion:

Diurnal cu field has formed across much of central Indiana early
this afternoon and will linger through late day. An axis of mid
level clouds drifting out of northern Illinois should expand into
the area by early evening...with increasing cloud cover overnight in
advance of an upper level wave and associated cold front. Scattered
convection will move across central Indiana mainly after 06Z with
additional showers possible in the immediate vicinity of the frontal
boundary Saturday morning. Will handle with PROB30s at all terminals
late tonight and early Saturday considering the scattered coverage
and low to medium confidence on impacts. Clouds will scatter once
the front passes by midday Saturday.

Generally light and variable flow is expected through the first half
of tonight then becoming southwest in the predawn hours as the front
approaches. Once the front passes Saturday morning...winds will veer
to northwest and increase to around 10kts. A few gusts at 15 to
20kts will be possible as well.


&&

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

$$

AVIATION...Ryan
DISCUSSION...Crosbie