453
FXUS63 KIWX 190814
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
414 AM EDT Tue Aug 19 2025

.KEY MESSAGES...

- Showers with some embedded thunderstorms will track across the region
  this morning. Some minor flooding concerns persist with
  additional rainfall across portions of northwest Indiana that
  received heavy rainfall over the past 24 hours.

- Additional scattered showers and thunderstorms are expected
  this afternoon with the greatest coverage expected generally
  south of US Route 24 across northern Indiana and northwest
  Ohio. A few strong storms are possible with localized heavy
  rainfall and isolated wind gusts to around 50 mph possible.

- Remaining hot and humid today, but cold frontal passage later
  today will bring less humid conditions for the remainder of
  the week.

- Much cooler conditions arrive for late weekend into early next
  week.

&&

.DISCUSSION...
Issued at 406 AM EDT Tue Aug 19 2025

An active convective pattern continues this morning with a renewed
round of showers and thunderstorms moving into northern Indiana and
southern Lower Michigan. This area appears to be developing
downstream of a mid/upper level trough and lift appears to be
aided by a rather extensive area of low/mid level frontogenesis
forcing from northwest Illinois into southeast Wisconsin. This
activity early this morning should be primarily elevated in
nature with less of a wind threat in comparison to earlier
storms. Main concern for the morning hours will be potential of
any hydro issues as these showers and storms are developing in a
zone of return positive theta-e advection and a region of PWATs
around 2 inches. A few pockets of heavy rainfall have occurred
over the past 24 hours, particularly across portions of north
central La Porte County in western St. Joseph County. This will
need to be watched as any additional moderate to heavy rainfall
will likely lead to at least some minor flooding issues this
morning. Coverage of these showers and storms should tend to
diminish heading to midday as the zone of stronger advective
forcing shifts east of the area.

A lagging mid level trough and southeast advancing sfc cold front
will likely be focal points for scattered convection again this
afternoon, but a good deal of uncertainty exists with coverage. It
is possible composite boundary and differential heating zone could
develop from residuals of morning convection. This could take
effective front/sfc convergence, just south/southeast of the local
area which would keep more vigorous afternoon convection just
outside of the local area to the east/southeast. However, with
lagging mid level trough and some larger scale frontal response,
still feel mid to high chance PoPs across NW Ohio and portions
of far northeast Indiana are still in order. The greatest
concern for isolated strong storms is primarily along and south
of US Route 24 corridor as HREF guidance depicts a moderate 2000
J/kg west-east oriented sfc based instability axis shifting
across these areas this afternoon. This better instability will
be a little southward displaced from the better westerly shear
across the southern Great Lakes into the eastern Great Lakes,
with deep layer shear generally 20 knots or less in the zone of
max instability. Guidance does indicate some drier mid/upper
tropospheric air punching into northern Indiana later today, and
this drier air overlaid with high near sfc moisture could
provide some favorability for isolated wet microburst setup.
This continues to be a low confidence isolated strong storm risk
given uncertainty in near sfc thermodynamics and effective
frontal placement this afternoon.

It will be warm and humid today, particularly across southern
locations. Peak afternoon heat indices should be limited to the low-
mid 90s however given what should be good deal of cloud cover
lingering and eventual transition to low level cold advection from
north to south.

The remainder of the work week still appears to be relatively
tranquil with broad northerly flow on southern periphery of Great
Lakes anticyclone. High should still be in the upper 70s to lower
80s, but humidity levels will be much lower.

Medium range guidance is still in reasonable agreement in a fairly
large shift in synoptic pattern as a stable wave pattern develops by
the weekend (western CONUS ridging, eastern CONUS troughing). A
reinforcing low level trough will likely mark the leading edge of
cooler air Saturday/Saturday night as it pivots through the region.
This will set up a period early next week with highs likely only
reaching low-mid 70s. Some small rain chance was left in on Saturday
as this reinforcing low level trough moves through.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 151 AM EDT Tue Aug 19 2025

VFR conditions to start the TAF period, deteriorating to
MVFR/IFR, particularly at KSBN overnight into Tuesday. A
decaying line of storms is moving towards KFWA this evening,
with the outflow moving through as of this writing. Light winds
may temporarily shift north/be variable for a bit before
shifting back to the southeast. Additional storms are on Lake MI
right now and will move through KSBN around 8z-12z, with
IFR/MVFR visibilities and ceilings possible. Behind that as the
front and winds shift to the W-NW, we could see some drizzle or
light rain persist through 17z or so-with ceilings around
700-1500ft. Expect improvement to MVFR by the afternoon. KFWA
will see rain pass between 13-17z, with showers and storms
lingering in the vicinity until around 20z. VFR conditions will
then persist through the end of the TAF Period.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...MCD