249
FXUS63 KIWX 170707
AFDIWX

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

.KEY MESSAGES...

- Thunderstorms possible today and tonight. Severe weather is
  not expected during this time.

- Severe storms likely Wednesday with damaging winds the
  greatest threat. Tornadoes are possible

- Hot this weekend through Monday with highs around 90 to 95
  with heat indices around 100 to 105 degrees.

&&

.DISCUSSION...
Issued at 135 AM EDT Tue Jun 17 2025

A very active scenario is unfolding that will extend through
the weekend. This pattern includes a good chance for severe
thunderstorms Wednesday followed later by hot and humid weather
arriving Saturday and persisting through Monday. Afternoon heat
indices during this latter time will be in the 90s to locally
as high as 105 degrees.

At the onset early this morning, lingering showers were draped
along the southern part of the forecast area from Marion to
Portland (Indiana). These showers were associated with a weak
short wave trof that was approaching from the west per EMC RAP
analysis. Diurnal conditions had stabilized since yesterday
afternoon helping to limit thunderstorm activity. More showers
and storms will spread back over the area today and tonight as
numerous impulses reach the area in fairly high zonal flow.
There will be a large diurnal "flare" in the activity which is
characteristically favored in the 19Z to 01Z window for this
time of year, especially near the solstice. GFS BUFKIT indicates
CAPEs at this time will range from 1000 to 1500 J/Kg.

There is a good chance for severe storms Wednesday, especially
late in the day and through the evening. The stage will become
set Wednesday for a very good chance for thunderstorms as a
strong impulse reaches the area in tandem with a surface
tracking northeast across Wisconsin and over Lower Michigan. A
band of anomalously strong 700 winds over 60 knots will arrive
Wednesday causing speed shear to increase. An early 2-3C lower
cap will erode with afternoon CAPEs approaching 2000 J/Kg.
Morning convection is highly questionable given this cap. Gut
feeling storms early Wednesday will be limited and not have much
of an effect on evening development. Prefer the GFS holding
back convection until close to 03Z. There should be explosive
convective development on a line across northern Indiana and
northwest Ohio. The line should move southeast just ahead of the
front. BUFKIT has the front passage by 01Z at SBN, 03Z at FWA
and later in the morning at AOH (Lima).

Lastly, hot and humid conditions will arrive this weekend as a
vast upper level high develops over nearly the entire east
CONUS. Center 500 mb heights are close to 6000 meters. High
temperatures will soar in the the 90s. Prefer the ECMWF with
high temperatures reaching 95 degrees. Given dew points of 70 to
75, corresponding max heat index vales will become widespread at
close to 100 degrees. There is a good chance heat headlines will
be issued as this event nears.

&&

.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...Skipper
AVIATION...Roller