752
FXUS63 KIND 271423
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1023 AM EDT Mon Jul 27 2026

.KEY MESSAGES...

- Hot and humid conditions today; heat index values above 105 over
  western central Indiana

- A thunderstorm complex is possible this afternoon with damaging
  winds and heavy rainfall the primary threats. Additional
  thunderstorms are possible overnight but confidence is low

- Rain free Tuesday-Thursday amid near to slightly below normal
  temperatures/humidity.

&&

.FORECAST UPDATE...
Issued at 1023 AM EDT Mon Jul 27 2026

Only minor updates this morning mainly concerning fog coverage and
cloud cover. Also trimmed PoPs back a bit as upstream convection has
weakened somewhat. Satellite still shows some unstable altocumulus
northwest of Lafayette, which some high-res guidance wants to
develop further. Will need to monitor this area over the next few
hours as atmospheric instability is high and sufficient shear is
present for strong thunderstorm potential. Actually getting
convection to initiate is the biggest hurdle through the morning.
CAM guidance can struggle greatly in low forcing situations with
high instability. Therefore, run-to-run consistency is likely to be
very poor and model uncertainty will be high. Take individual model
runs with a grain of salt through this afternoon. Confidence is
likely to improve this evening as a more defined area of forcing
arrives from the north in the form of a potent short wave. This
short wave is expected to bring additional convective chances into
tonight.

&&

.DISCUSSION (Today through Sunday)...
Issued at 225 AM EDT Mon Jul 27 2026

Today through Tonight

An upper level ridge will continue to build eastward within modest
westerly WAA. This WAA within the lower levels will continue to push
temperatures and dew points well above normal building deep
instability across the region. MUCAPE values will exceed 3000 J/kg
by noon, with values likely pushing above 4000 J/KG towards the
middle of the afternoon through the evening. Shear will also be
plentiful as the jet stream remains aloft, with 35-50kt of effective
shear. The combination of high instability and plentiful bulk shear
will lead to a potent airmass, but the source of upward motion to
initiate these thunderstorms is still a bit of an enigma. There is
building confidence on a convective complex initiating along a weak
shortwave early this morning over the upper Great Lakes region, with
a majority of the CAMs pushing this complex southward into the Ohio
Valley this afternoon. The primary threat with this thunderstorm
complex will be wind gusts of 60-80MPH, but small hail and an
isolated tornado cannot be completely ruled out.

Even with this additional confidence in general timing, specifics on
timing and location remain fairly uncertain within the previously
mentioned window due to somewhat ambiguous storm motions. Unlike
strongly forced events, storm motion will greatly depend on the
placement of any developing cold pools and its relation to the
ongoing thermodynamic parameters. This could lead to a storm motion
range from 340 degrees to potentially 20 degrees over the course of
this event. Also, CAMs notoriously struggle with translation speed
and longevity of these thermodynamically induced convective
complexes due to underestimating cold pool density and interaction
within the ongoing environment. This is a lot of information to say,
be very hesitant on taking any CAM reflectivity output verbatim this
afternoon, and thus confidence in thunderstorm passage for any
specific location will likely have to wait until 3-6 hours ahead of
arrival.

After this first convective threat this afternoon, additional
thunderstorms are expected to develop along and ahead of a diffuse
frontal boundary between 01-08Z. As with the first round, confidence
is fairly low on any specifics, but the overall atmospheric
parameters will remain potent enough for an additional severe threat
with wind once again being the primary threat. This time, greatest
confidence will shift towards NE portions of the area, as this
portion looks to have slightly greater surface confluence and
therefor a greater confidence in convective forcing.

The temperature forecast today will also be fickle and will greatly
depend on thunderstorm timing and location. The WAA previously
mentioned will push a very humid airmass into the region with dew
points likely nearing 80 and temperatures pushing into the low 90s.
This combination will likely lead to a prolonged period of heat
index values above 100 and a few hours between 105-110. For this
reason, a Heat Advisory has been issued. The current ending time for
the advisory will be 01Z, but this could be canceled early depending
on cooling impacts from afternoon convection. As stated, a frontal
passage is expected overnight into tuesday morning. The front is not
strong, but will still push temperatures back towards seasonal for
the coming week.

Tuesday through Sunday...

Strengthening hot and humid upper subtropical ridge over western
North America...will be offset partially by progression of smaller
weaknesses plunging from north-central CONUS to Ohio Valley...which
will likely result in slightly below-normal warmth and humidity
across central Indiana through at least Thursday morning.  First
cool front progged to push south across the region around dawn
Tuesday, with northerly gusts actually up to 20-25 mph for many
locations...only allowing low to mid-80s for central/northern
counties, and noticeably lower humidity for all by late evening.

Tuesday night to Wednesday night to host most pleasant conditions,
as weak but amplified surface high pressure builds south from James
Bay into much of the Midwest...and ridge axis` alignment near the
Wabash Valley maintaining lower dewpoints and readings for most of
the region into early Thursday...with highs Wednesday around 80-85F
amid more September-like breezes...flanked by consecutive overnights
with lows around 60F.

Late work week to transition warmer and touch more humid as upper
ridge tries to build east across central US...which will at least
push the surface high out of the region, returning light southerly
breezes and perhaps a few afternoon showers/t-storms for Friday-
Saturday. Low confidence in any 90s returning late in the period as
next northern mini-wave plunges/slows down across the Midwest during
the weekend, with accompanying clouds...and what should eventually
be a flip back to northerly winds and only low-chances of convective
showers by the very end of the long term, with near normal ranges in
the 60s/80s.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 623 AM EDT Mon Jul 27 2026

Impacts:

- Fog could linger for the first hour of the TAF. Prevailing MVFR
  with tempo IFR to LIFR

- Storm complexes may impact the area this afternoon and again
  late this evening into the overnight.

- Non-thunderstorm gusts out of the south this afternoon up to 18kt

Discussion:

Low lying fog is expected for the first hour at KLAF and KHUF,
this should clear quickly after 13Z. Some lingering MVFR clouds
are possible early, but should become scattered by 15Z, with
occasional wind gusts to 15-18kt this afternoon.

Still a fairly uncertain thunderstorm forecast ahead, but
confidence is growing is a organized line arriving this afternoon
between 18-22Z. Additional thunderstorms are possible overnight at
KLAF and KIND, but confidence in occurrence is low. A frontal
passage overnight will shift winds from the SW to NW with winds
remaining below 10kt.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM EDT this evening for INZ028-029-035>037-
043>047-051>055-060>064-067>071.

&&

$$

UPDATE...Eckhoff
AVIATION...Updike
DISCUSSION...Updike/AGM