116
FXUS63 KIWX 110717
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
317 AM EDT Fri Jul 11 2025

.KEY MESSAGES...

- Several chances of storms through the weekend, with isolated
severe weather and locally heavy rainfall possible at times.

- Greatest risk of thunderstorms will come in multiple rounds, but
lower confidence in timing. Current indication suggest best chances
during the afternoon and evening hours through Sunday.

- Hot and humid conditions for the weekend, with highest heat
indices expected in the 95 to 100 degree range for Saturday
afternoon.

- Brief shot of dry and less humid weather Monday, but heat is
expected to return for Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 315 AM EDT Fri Jul 11 2025

A decaying MCS across northeast IL/northwest IN has sparked some
renewed convective activity over past hour across NW Indiana at the
leading edge of an associated MCV. Some elevated return low level
theta-e advection is occurring in advance of this disturbance which
is providing just enough elevated instability (MUCAPES 500-750 J/kg)
for a few narrow bands of thunderstorms. A pocket of 35 knot
effective shear appears to be localized to the vicinity of the MCV
this morning, but limited instability magnitudes should temper the
overall strength of convection this morning. Some brief heavy
downpours will be the most likely thing to watch with any isolated
storms this morning, and possibly some brief pea sized hail. These
showers and embedded storms will likely work across the rest of the
northern portions of the area this morning, but likely in a more
scattered fashion as this forcing continues to outpace the better
upstream elevated instability. Some diurnal upswing could occur
across far northeast Indiana/northwest Ohio/south central Lower
Michigan toward mid morning as this small scale wave departs.

Looking ahead to this afternoon, another convectively enhanced short
wave is likely to emanate out of the Corn Belt with a more
impressive ongoing convective complex early this morning. Mid
level steering flow would tend to favor the western/southern
Great Lakes for a favored track with this potential short wave,
which should approach during peak heating. However, this
potential small scale wave will likely be entering a larger
scale synoptic pattern that would tend to favor subtle mid level
height rises across the region, so some low confidence exists
with potential convective redevelopment this afternoon. The
environment would be characterized by moderate instability and
fairly low shear, with better shear profiles likely tied to more
favored track of MCV just northwest of the local area. Any
storms this afternoon would have a potential of some localized
heavy rainfall and isolated stronger wind gusts of 50+ mph.
Otherwise, it will be hot and humid today as reservoir of richer
moisture across the Mid MS Valley spreads east, but will be
tempered some with eastward extent as mid level ridging may be a
bit more stubborn to hold.

Greatest isolated severe threat could materialize this
evening/early overnight as a more substantial synoptic wave
(again likely convectively enhanced) ejects east/northeast out
of the Central Plains. HREF guidance continues to suggest best
instability axis sprawled from west central IL into NW Indiana
this evening in advance of this feature. Greater severe
potential may hang just west of local area with attendant better
shear profiles, but some isolated wind/hail threat is possible
this evening, particularly from northwest IN into SW Lower
Michigan. Warm cloud depths in excess of 11K ft, minimal
magnitudes to Corfidi vectors due to uniform deep SW flow, and
PWATs over 1.5 inches could support a locally heavy
rainfall/flood threat across these locations.

Forecast confidence in convective evolution inherently wanes for
Saturday and beyond due to the integrated uncertainty arising from
the dependence of upstream convective evolution. The
aforementionedwave from tonight, should be lifting across the
area and eventually to the eastern Great Lakes during the day
Saturday. A few focal points of thunderstorm development are
possible Saturday afternoon, one along and east of I-69 where
some better pre-frontal moisture convergence/pooling is possible
as the lead short wave departs. Further upstream, a larger
scale synoptic response is possible with low level troughing
building into the western Great Lakes downstream of a larger
scale upper trough across the upper Midwest. However,
instability magnitudes may be more tempered across western
portions of the area. The northeast quadrant of the local
remains in SWODY2 Slight Risk for severe storms as shear
profiles will likely be a bit more pronounced across south
central Lower Michigan/far NE Indiana which should give some
limited spatial overlap to best instability along and east of
I-69. This threat will be dependent on timing/strength of the
lead short wave Saturday. If convection is more delayed/lower
coverage Saturday, heat indices could make a run near the upper
90s to 100 across the far east in proximity of the better pooled
moisture.

Sunday will offer another chance of storms although evolution of the
larger scale upper trough Sunday could focus this threat across
southeast third of the area. Decent instability is a good
possibility Sunday PM ahead of the cold front, but shear profiles
are likely be on the marginal side again.

A break in the convective chances and less humid conditions
arrive for early week, but this break appears to be short-lived
as a more active northern stream pattern dampens weak upper
ridging across the Great Lakes once again. This should support
another period of several storm chances along with a potential
of more 90s heat indices in the Tue-Thu timeframe.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 102 AM EDT Fri Jul 11 2025

Convection over Chicago will eventually move eastward and impact
KSBN later this morning. Local environment is very stable and it
will take time for the nocturnal LLJ to ramp up and advect
sufficient moisture/instability into the area. Best chances for
storms at KSBN currently appear to be around 12Z though a few
showers may move in earlier. After that, another round is
possible around 00Z with diurnal destabilization but confidence
in timing and coverage is very low at this stage. Much lower
thunderstorm chances at KFWA given displacement from weak
frontal boundary/better moisture convergence. A stray storm
can`t be ruled out either during the late morning or Friday
evening but confidence is too low to mention in the TAF.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...AGD