129
FXUS63 KIND 031247
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
847 AM EDT Fri Jul 3 2026

.KEY MESSAGES...

- Extreme Heat Warning in effect through 8 PM today, Heat
  Advisory afterwards through 9PM Saturday

- Thunderstorm chances will increase after 7PM today with downbursts
  possible

- Greater storm coverage for Saturday with a lower threat for severe
  weather

&&

.FORECAST UPDATE...
Issued at 847 AM EDT Fri Jul 3 2026

Surface analysis late this morning shows strong high pressure in
place over WVA. Low pressure was found over western KS. A weak
outflow boundary from yesterday/s convection was found south of MIE
and toward Greenfield. Aloft, water vapor showed a strong area of
high pressure over the Carolinas and VA, and a tropical plume of
moisture was streaming north across TX and OK toward the upper
midwest. Indiana was still under the influence of of this strong
high pressure system, allowing a stagnant air mass, with very warm
temperatures.

As the previous discussion states, forecast soundings suggest a very
unstable column today, but warm temperatures within the mid levels
and a lack of forcing should limit convection potential this
afternoon. Some CU development is suggested, but HRRR shows any
convection, albeit very isolated remaining across northern Indiana
through the afternoon hours. Thus precipitation will not be expected
through this afternoon. Given the little change in the overall air
mass, high temperatures and heat index values will be similar to
persistence. Overall, ongoing forecast remains in good shape.

&&

.DISCUSSION (Today through Thursday)...
Issued at 131 AM EDT Fri Jul 3 2026

Overview.

Patchy fog early this morning will give way to another day of
high heat and humidity, with heat indices above 105 degrees.
Thunderstorms are expected to develop during the late afternoon
and evening hours both today and tomorrow, presenting a severe
localized downburst and damaging wind threat. A slow cooling trend
begins Sunday, though daily chances for scattered showers and
storms will persist through mid-week.

Today through Saturday.

Near-surface saturation from residual boundary layer moisture and
light to calm winds beneath a lingering low-level inversion will
support patchy radiation fog development early this morning. This
will primarily impact river valleys and low-lying areas before
rapidly dissipating by 13Z with the onset of diurnal mixing.

Thereafter, focus shifts to both the heat and storm chances today.
While the anomalous sub-tropical ridge across the Ohio Valley begins
to subtly deamplify and suppress southward, 850mb temperatures
around +22C to +24C and intense diabatic heating will act on a
high theta-e airmass. With surface dew points forecast in the mid
to upper 70s, convective temperatures will quickly be breached in
the low 90s, driving peak afternoon heat indices between 105 and
110 degrees both Friday and Saturday.

Weakening large-scale subsidence will allow the capping inversion
near 700 mb to erode, clearing the way for convective initiation
during the peak diurnal heating windows. For Friday, timing for
isolated to scattered convective development is centered between 23Z
and 04Z, focusing along subtle mesoscale convergence zones or
differential heating boundaries. On Saturday, a weak, low-amplitude
shortwave traversing the flattening ridge periphery will provide
slightly stronger synoptic forcing, shifting the initiation window
slightly earlier to 19Z to 03Z and yielding higher storm coverage.

Thermodynamics both days are exceptionally potent, with MLCAPE
values progged to exceed 3500-4000 J/kg. While weak deep-layer
vertical wind shear of less than 20kts will limit organized, long-
lived updrafts or supercellular structures, the environment is
classic for severe pulse convection and microbursts. Model soundings
display an ideal profile for severe downburst generation: PWAT
values near 2.1 inches maximizing precipitation loading aloft,
combined with steep low-level lapse rates with 0-3 km lapse rates
exceeding 7.5 C/km and a dry mid-level layer creating DCAPE values
over 1300 J/kg. Updrafts will rapidly accelerate, load heavy water
cores, and subsequently collapse as intense negative buoyancy and
evaporative cooling accelerate air downward. This may result in
localized, significant straight-line downburst winds capable of
exceeding 60-70 mph. The severe weather threat for today looks
higher than Saturday with storm coverage on Saturday looking greater
compared to today.

With the heat indices expected to top out in the low 100s again
today, opted to issue a Heat Advisory with the known uncertainty as
to storms bringing earlier relief than the current 9 PM endtime.
With the extended stretch of heat already combined with the
holiday weekend, felt the headline was warranted even as we remain
just under typical criteria.

Sunday through Thursday.

The synoptic pattern undergoes a more noticeable transition by
Sunday as the sub-tropical ridge is forced further into the Gulf
Coast states, positioning central Indiana on the southern periphery
of an active, progressive northwest flow regime aloft. This will
open the door for a series of low-amplitude shortwave troughs and
embedded convective impulses to traverse the Great Lakes and Ohio
Valley through the mid-term period. While the extreme, warning-level
heat will subside as 850mb temperatures drop back toward +18C, a
warm, moist, and moderately unstable airmass will linger,
maintaining daily opportunities for scattered showers and
thunderstorms.

Convection during the Sunday through Monday timeframe will remain
largely diurnal and mesoscale-dependent, focusing along residual
outflow boundaries. Pulse severe hazards, specifically localized
downbursts, will remain a secondary threat but with lower overall
coverage as thermodynamics become less extreme.

By Tuesday into Wednesday, long-range ensemble guidance indicates a
deeper, more cohesive northern stream shortwave digging out of south-
central Canada. This feature will propel a distinct surface cold
front southward through the state, serving as a robust linear
forcing mechanism for more organized shower and thunderstorm
development. In the wake of this frontal passage, strong high-
pressure of Canadian origin will overspread the Midwest, inducing
robust cold air advection and dropping a much drier, cooler airmass
into the region. This will effectively suppress temperatures and
humidity back to slightly below seasonal averages by next Thursday.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 605 AM EDT Fri Jul 3 2026

Impacts:

- Isolated TSRA, mainly from 23Z to 04Z.

Discussion:

VFR conditions through much of the day outside of the low chances
for convection later today. Diurnal cu will become more prevalent
after 16Z with storm chances increasing as early as 22Z and coverage
being greatest from 00Z to 03Z. Storms look to be isolated with the
best chances towards LAF, but any storm could produce downbursts
capable of briefly strong wind gusts. Outside of convection, winds
are expected to maintain a generally southwesterly component through
the forecast period at 8-12kts outside of a period of near calm
winds through 13Z.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning until 8 PM EDT this evening for INZ021-
028>031-035>049-051>057-060>065-067>072.

Heat Advisory from 8 PM this evening to 9 PM EDT Saturday for
INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

UPDATE...Puma
AVIATION...White
DISCUSSION...White