569
FXUS63 KIWX 182312
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
712 PM EDT Fri Jul 18 2025

.KEY MESSAGES...

- A line of strong to severe thunderstorms is expected Saturday
  afternoon and evening, with damaging winds as the primary
  threat.

- Locally heavy rainfall from Saturday`s storms could lead to
  isolated instances of flooding, though the progressive nature
  of the storms may limit a more widespread threat.

- A significant a prolonged period of dangerous heat and
  humidity is expected to build in from the middle to the end of
  next week, with heat indices in excess of 100 degrees
  anticipated.

&&

.DISCUSSION...
Issued at 115 PM EDT Fri Jul 18 2025

A quiet and pleasant day is on tap for the CWA today as high
pressure provides us with dry conditions and a touch lower
humidity. This will be short-lived, however, as southerly flow
develops tonight, advecting much warmer/humid airmass that will
set the stage for an active Saturday.

The primary challenge in the near term is a multi-hazard event
on Saturday, as the area will reside under a very unstable and
moisture- rich environment out ahead of an approaching cold
front. SPC has placed the entire area under a Slight Risk (Level
2 of 5) for severe thunderstorms. The main time to watch is
from 12 to 6pm, but storms may occur an hour or two on either
side of that. Ample instability is forecast, with HREF
suggesting CAPE values around 2,000 J/kg. This will combine
with marginally sufficient wind shear to support an organized
line of strong to severe storms moving through the area during
the PM hours. The main threat will be damaging winds, but
secondary threats include small hail and a low-end chance for
line- embedded tornadoes.

In addition to the severe threat, very high moisture content
characterized by PWATs approaching 2in will lead to a threat of
heavy rainfall. Consequently, we have also been placed under a
Slight Risk for Excessive Rainfall by WPC. Storms will be
capable of producing torrential downpours that could lead to
isolated flooding. However, the expected progressive storm mode
should help limit a more widespread flooding threat.
Significant uncertainty remains regarding the impact of any
potential morning convection. If widespread showers and storms
form in the morning, they could stabilize the atmosphere and
limit the afternoon storm potential, a common forecast problem
in the Midwest.

Cooler and drier air will filter in behind the front for
Sun/Mon, providing a brief break from the active weather. During
this Sunday through Tuesday timeframe, trends suggest that any
organized complexes of storms will remain just to the south and
west of our region, although this will need to be monitored -
especially for Sunday where confidence in northern extent of
precipitation is still a bit uncertain.

The focus then shifts to a major pattern change for the middle
and end of next week. There is high confidence that a strong
upper-level ridge will build across the Central US and take hold
over our region. This will bring a prolonged period of
dangerous heat and humidity, likely from Wednesday through next
weekend. High temperatures are expected to be near or above 90
degrees with dewpoints in the 70s, leading to potentially
dangerous heat indices in excess of 100 degrees. This heat dome
pattern will establish a Ring of Fire convective regime with
storm complexes riding along the northern edge of the ridge,
bringing periodic rain chances back into the forecast for the
latter part of the week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 707 PM EDT Fri Jul 18 2025

High pressure over the eastern Great Lakes overnight provides
tranquil conditions but also the chance for ground fog. KFWA and
its southeasterly wind (albeit weak) will permit some moisture
advection from the Ohio Valley. Forecast soundings depict an
ample inversion for BR/FG overnight. This signal is weaker at
KSBN. Given I inherited BR at KFWA, I`ve kept that going but the
trend will need to be monitored at KSBN.

In the afternoon, a line of thunderstorms is anticipated.
Timing of the storms offers medium confidence. The line will
move in from the northwest, thus a wind from 300-330 is probable
as the line moves through.

&&

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

&&

$$

DISCUSSION...Norman
AVIATION...Brown