690
FXUS63 KIWX 190654
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
254 AM EDT Thu Jun 19 2025

.KEY MESSAGES...

- Showers and isolated storms will exit the area late this morning.

- Heat and humidity will steadily build Friday through Sunday.
  Heat indices Sunday and Monday will be around 100F.

- Mainly dry conditions are expected from this afternoon through
  Monday.

&&

.DISCUSSION...
Issued at 254 AM EDT Thu Jun 19 2025

Midlevel trough axis remains just upstream per early morning water
vapor imagery. Resultant CVA and some elevated deformation/fgen
(mainly over MI) will continue to support SCT showers over the area
through the morning. While far better moisture/instability is
shunted well to our east by now, models suggest cool midlevel temps
and some marginal surface heating by mid-morning will be enough to
support some non-zero CAPE and a few isolated storms. Will therefore
add an isolated thunder mention but no strong or severe storms are
anticipated. Any appreciable rainfall rates within the isolated
storms will likely be insufficient to cause any flooding concerns
given quick storm motion and overall low coverage. Trough axis exits
our eastern zones around 18Z and will signal the end of precip
chances. Should see a fair amount of sun by late afternoon but highs
will only recover into the mid/upper 70s.

The big story in the long term remains the excessive heat. As
today`s trough exits, a very strong and large upper ridge (500mb
heights very near 600 dam) will take shape over the eastern CONUS.
Highs steadily climb over the region from Fri-Sun as this ridge
takes shape and SW flow develops from the Southern Plains to the
Great Lakes. Most of this period is expected to be dry though will
have to keep an eye on Fri night as a few showers/storms could clip
our far north as the primary warm front lifts through MI. Dry
conditions are assured Sat-Mon as this ridge builds. Sun and Mon
currently appear to be the hottest days with highs in the mid 90s
and dewpoints in the 70s yielding heat indices around 100F. There is
some concern that, due to the cool spring/delayed start, the local
crops may not be quite mature enough to support solid low-mid 70s
dewpoints necessary to yield heat indices over 100F. However, the
widespread 0.5-1" of rain that fell will certainly help in this
regard. Held close to NBM initialization for now but the 72-75F
dewpoints may need to be adjusted down slightly in future forecasts.
Given this uncertainty, it remains too early for an excessive heat
watch.

The NBM (heavily influenced by the convection-loving GFS and its
ensembles) suggests relief by the middle of next week in the form of
a weak cold front and SCT-NUM storms. The ECMWF paints a much
bleaker picture suggesting the "cold front" remains draped over
central MI and precip never quite reaches our area (perhaps just
scraping our northern zones). Looking at the overall pattern, the
ECMWF may be correct. Even on the deterministic GFS there is very
little mid/upper support for a front to push far enough south to
support all of that convection throughout the Ohio Valley. There is
still plenty of uncertainty this far out though and didn`t mess with
NBM PoP`s too much. Of course the uncertainty in PoP`s spills over
into uncertainty with max temps and the potential extension of early-
week heat wave. Still plenty of time to nail down those details
though.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1236 AM EDT Thu Jun 19 2025

A deep surface low was over Lower Michigan near GRR. This system
was spreading showers and low clouds into northern Indiana and
northeast IL. The low will move east out of the area by late
today and allow clearing skies. IFR clouds are likely to persist
until mid morning. Used NAM BUFKIT favoring showers ending by
late morning followed by clearing close to 18Z.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.

&&

$$

DISCUSSION...AGD
AVIATION...Skipper