944
FXUS63 KIND 271857
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
257 PM EDT Mon Jul 27 2026

.KEY MESSAGES...

- SEVERE THUNDERSTORM WATCH UNTIL 9PM

- HEAT ADVISORY UNTIL 9PM

- Thunderstorms this afternoon and evening with severe weather
  likely. Damaging winds are the primary hazard. Secondary hazards
  of large hail, tornadoes, and flooding also possible.

- Rain free Tuesday-Thursday amid near to slightly below normal
  temperatures/humidity...with northerly breezes Tuesday, Wednesday

&&

.DISCUSSION (This evening through Monday)...
Issued at 256 PM EDT Mon Jul 27 2026

Satellite and radar imagery shows a large complex of showers and
thunderstorms over the Chicago area as of 2pm. This cluster of
storms is likely going to impact our area to some extent this
afternoon and evening. At the surface, a distinct axis of greater
instability (3000-4000 J/Kg MLCAPE) extends NW to SE through most of
central Indiana. Surface winds are generally southwesterly to the
west of this boundary. Along it, light and variable conditions are
noted. To the east, a southeasterly wind is observed.

Aloft, strong southeasterly shear between 45-55kt extends over most
of Illinois, Indiana and Ohio. This mean shear vector is almost
exactly parallel to the instability axis. Further to the north, a
potent mid-level vort max is shown which was the catalyst to ongoing
convection. Now that storms have initiated, the immediate mesoscale
concern is how storms evolve coming into our CWA in the next few
hours.

One scenario is that the storms develop a strong cold pool and begin
propagating southeastward along the instability axis. This is
plausible since the shear vector points southeastward along this
axis, and cold pool shear balance will be easier to achieve. In this
scenario, severe winds will be the primary hazard. However, embedded
supercells, as have been seen over Chicago this afternoon, would be
capable of all hazards including large hail and tornadoes.
Additionally, a QLCS tornado threat may develop if the low-level jet
ramps up significantly this evening.

A second scenario is similar to the one above, but the low-level jet
ramps up a bit earlier and storms propagate more southward owing to
greater upshear growth. This would send the storm cluster over our
western CWA with similar hazards to scenario one. All in all, the
main difference is timing and influence from the low-level jet.
Guidance shows the low-level jet increasing substantially around 02z
to between 30-40kt at 925mb. However, the storms may already be
through our area by that point. Renewed development on the western
edge could occur if a residual cold pool lingers over the area.
Flooding could occur if storms begin redeveloping over the same
areas as the initial round of activity.

After tonight, the vort max and associated surface low depart
eastward with a cold front sweeping through by dawn. Northern winds
usher in cooler and drier air with temperatures falling towards
normal for the remainder of the week. Another vort max may arrive
this weekend, embedded within weak westerlies aloft, bringing
precipitation chances back by Friday. Given the weak flow and
likewise weak vort max it would seem prudent to keep precipitation
chances capped at chance (40 percent). Model uncertainty is high, and
such weak/subtle features can be hard to pin point this far out.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 122 PM EDT Mon Jul 27 2026

Impacts:

- Strong to severe thunderstorms possible at all sites late
  afternoon into the evening

- Wind gusts around 18-21KT during the day on Tuesday

- Potential for fog or low ceilings near daybreak Tuesday

Discussion:

Strong to severe thunderstorms have developed along the western
shore of Lake Michigan, and are likely to shift southward along the
instability gradient into the region later this afternoon into this
evening. Upscale growth will likely result in a bowing complex,
though uncertainty in its latitudinal extent and exact timing still
exists. Will carry a PROB30 group at all sites as early as 20Z at
LAF and as late as 03Z at BMG. Additional activity cannot be ruled
out in the wake of the storms, but is too uncertain to include at
the moment.

Depending upon the degree of clearing late tonight, some fog and/or
low ceilings will be possible near daybreak Tuesday, but is again
too uncertain to include at this time. This will be refined as able
in future packages.

Winds will shift from the west/southwest to the north/northwest with
frontal passage late tonight into Tuesday, with gusts during the
daytime hours to around 18-21KT.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM EDT this evening for INZ021-028>030-
035>037-039-043>048-051>056-060>064-067>071.

&&

$$

AVIATION...Nield
DISCUSSION...Eckhoff