446
FXUS63 KIWX 170530
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
130 AM EDT Tue Jun 17 2025

.KEY MESSAGES...

- Isolated showers and storms possible (20-30%) along and
  southeast of US 24 this afternoon into Tuesday morning.

- Additional chances (20-40%) for storms Tuesday afternoon-evening
  into areas mainly west of Interstate 69 in IN and MI.

- Thunderstorms likely (50-80%) on Wednesday, particularly mid
  afternoon through the evening when severe storms and heavy
  rainfall will be possible.

- PM peak heat indices may near 100 degrees this weekend into early
  next week.

&&

.DISCUSSION...
Issued at 234 PM EDT Mon Jun 16 2025

Mid level shear axis may activate a weak low level trough and
moisture axis for a few showers/storms later this afternoon through
Tuesday morning, mainly along and south of the US 24 corridor.
Meager shear and instability profiles should limit any isolated
storms to brief downpours and a few lightning strikes at worst late
this afternoon into early this evening.

For Tuesday afternoon and evening, convection potentially develops
over IA/nrn IL and makes eastward progress into western zones later
in the afternoon and evening. Airmass will be unstable, but any
convective activity will be outrunning more favorable flow/forcing
hinting at outflow dominant and weakening convection into mainly
western portions of the forecast area. Still could see some gusty
winds, especially if a MCV emerges with a slightly stronger wind
field than modeled.

On Wednesday, moist 70F sfc dewpoint and 1.7-2" PWAT air becomes
better established within increasing low-mid level southwest flow
preceding an approaching mid level trough and associated sfc frontal
wave. This may make for an active day locally with any lead MCS
activity and associated composite outflows supporting AM
shower/storm chances. It will be the the evolution of this activity
(cloud debris/outflow boundaries) that dictates if and when strong
to severe convection becomes a concern mid afternoon through the
evening. Low-mid level southwest flow ramps up resulting in more
favorable shear profiles by this time, with any heating leading to a
moderately unstable boundary layer along and south of any pre-
frontal features, and possibly the primary cold Wed night. Mesoscale
details are obviously uncertain 3 days out, but definitely will
continue to closely monitor as we approach this potential
severe/hydro event.

Post-frontal air mass will provide brief relief from the humidity on
Thursday with any renewed, diurnally driven, convection likely
focused off to the north with a trailing secondary mid level
impulse. Thereafter, deterministic and ensemble guidance have
remained consistent in upper ridging expanding northeast into the
Great Lakes with the warmest and most humid airmass of the season
building in this weekend into early next week. Low chances (10-20%)
that some convection could sneak in on the leading edge of the
building riding around the Friday night-Saturday periods, better
chances north.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 130 AM EDT Tue Jun 17 2025

An area of vorticity slowly meandering northward overnight into
Tuesday morning allows for a resurgence of showers and
thunderstorms. Severe weather is not expected with these given a
lack of shear. However, the chance is there to receive some MVFR
flight conditions (probably lowered visibility from storms) between
13z and 16z so will go with a prob30 group to highlight this
possibility. Otherwise, expect VFR conditions to prevail through the
first 18 hours of the period. Some chance of showers and storms is
also possible after 00z this evening near SBN, but not enough
confidence is there to insert it for this issuance. Winds are
expected to veer from southeasterly to more southwesterly by the end
of the period.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078-177-
     277.
MARINE...None.

&&

$$

DISCUSSION...Steinwedel
AVIATION...Roller