978
FXUS63 KIND 021313
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
913 AM EDT Tue Sep 2 2025

.KEY MESSAGES...

- A cold front with showers and thunderstorms expected to arrive
  on Wednesday

- Another round of cooler/drier air late week into next weekend.

&&

.FORECAST UPDATE...
Issued at 913 AM EDT Tue Sep 2 2025

No major changes needed to the ongoing forecast with conditions
generally evolving as expected. Morning temperatures are rapidly
rising into the low to mid 60s with dew points running 2-3 degrees
above the forecast, so adjusted those upwards through noon but don`t
plan on making additional upward adjustments into the afternoon as
mixing out of moisture should begin over the next few hours as the
boundary layer deepens.

Afternoon highs in the low 80s look reasonable with the expected
plentiful sunshine but generally cooler temperatures aloft helping
to limit the higher-end temperatures. Diurnal cu should be a bit
more widespread today compared to recent days with latest hi
resolution soundings showing saturation at the top of the boundary
layer by mid to late afternoon.

&&

.SHORT TERM (Today and tonight)...
Issued at 300 AM EDT Tue Sep 2 2025

Quiet and generally clear weather is expected through the short-term
period despite deep troughing overhead. At the surface, high
pressure is giving way to an inverted trough which extends along the
Ohio River from about Evansville southward. Guidance shows a plume
of moist near-surface air slowly lifting northward in conjunction
with this trough. Most guidance keeps it just south of our CWA
border across southern Indiana and into Kentucky. However, a few
members do bring moisture into our far south.

The primary result of this increased moisture will simply be a
muggier day for those affected. However, some guidance hints at a
pop-up shower or storm due to increased convective instability
produced by the moisture and warm air. The best chance of this would
be where the moisture is present, which is across our far south. The
overall chance seems low, 20 percent or less, but it cannot be ruled
out.

Elsewhere, a mainly sunny day with light and variable winds is
expected. Temperatures should rise into the low 80s for most.

Tonight will be similarly quiet. Fog is not expected due to mainly
dry air in place. However, the aforementioned moisture plume across
our south may allow for some patchy ground fog to develop by
Wednesday morning. Another subtle change is surface winds becoming
southwesterly by sunrise Wednesday in response to an approaching
cold front. The cold front and its effects will be discussed in the
Long Term section.

&&

.LONG TERM (Wednesday through Monday)...
Issued at 300 AM EDT Tue Sep 2 2025

Upper-level analysis shows large-scale troughing over the Midwest
and northeastern US. Ensemble guidance is in good agreement showing
this pattern holding steady through remainder of the week. Troughing
deepens significantly Thursday into Friday before flattening
somewhat this weekend.

The next decent chance of rain looks to be in the Wednesday/Thursday
timeframe. Guidance is showing low pressure strengthening and
occluding to our north, with a cold front passing through the area
as well. Surface moisture could creep further north in response to
the deepening system.

The cold front mentioned above looks to arrive late in the day on
Wednesday. Therefore, most of the day prior will be like today with
warm and sunny conditions. However, guidance is in very good
agreement showing showers and thunderstorms developing along the
approaching boundary over Illinois. These gradually work their way
into Indiana around mid afternoon continuing through the evening and
into the overnight. Shower and storm activity may persist until
Thursday morning over southern portions of our area. Storm mode
should be quasi-linear since shear vectors aren`t exactly parallel
to the front. However, given the strong forcing present along the
boundary itself, storms should gradually grow into a line as cold
pools develop and congeal. Severe weather is not anticipated due to
modest CAPE and weak shear. However, an isolated strong wind gust
cannot be ruled out especially in any bowing line segments.

Another chance of rain may occur Friday into Saturday as a shortwave
embedded in the deeper trough drops southward. Guidance diverges
significantly with this feature so confidence on any impacts is low.

Regardless of rainfall, an unseasonably cool air mass looks to drop
southward behind the front. ECMWF/GFS deterministic guidance shows
850mb temps between 3-6 degrees C, which could allow for low
temperatures potentially into the upper 30s assuming ideal
radiational cooling (clear skies and light winds). Blended guidance
has low to mid 40s this weekend, which seems reasonable for now
given the uncertainty in strength/position/timing of the occluding
low. The blend, however, shows highs in the mid to upper 60s
Thursday through Sunday. This may be a bit pessimistic, since the
sun angle is still quite high and we have recently been running
warmer than guidance under optimal boundary layer mixing conditions.

Uncertainty in the larger-scale pattern returns early next week, as
the ECMWF and GFS diverge regarding the longevity of deep troughing.
Both models at one point showed troughing breaking down with modest
ridging taking hold...but that no longer appears the case (GFS shows
ridging and ECMWF retains troughing). The signal for prolonged
troughing, albeit weaker, is now present within guidance once again.
As such, temperatures in the long range have trended downward from
previous forecast issuance.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 628 AM EDT Tue Sep 2 2025

Impacts:

- None

Discussion:

VFR conditions are expected through the TAF period.

A light northeasterly wind is expected to become light and
variable this afternoon and through tonight. Winds pick up a bit
and become southwesterly on Wednesday ahead of a cold front. That
front is expected to bring showers and thunderstorms later
Wednesday but after the end of the current TAF period.

Clouds will be limited to diurnal cumulus and high cirrus at
times.


&&

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

$$

UPDATE...White
SHORT TERM...Eckhoff
LONG TERM...Eckhoff
AVIATION...Eckhoff