326
FXUS63 KIWX 110502
AFDIWX

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

.KEY MESSAGES...

- Several rounds of rain/storms are possible over the next few
  days, mainly Friday morning and then again late Saturday into
  Sunday morning.

- A few storms could be strong to severe over the weekend, with a
  Marginal Risk for severe weather.

- Isolated instances of flooding are possible Saturday night
  into Sunday morning.

- Hot and humid Friday and Saturday with heat indices in the
  mid to upper 90s.

- Mainly dry with continued heat and humidity into early next
  week.

&&

.UPDATE...
Issued at 1001 PM EDT Thu Jul 10 2025

A cluster of convection had developed over northern IL earlier
this evening and is currently moving eastward at about 15 mph.
This convection has been for the most part been weakening and
the expectation is for it to weaken further before entering our
the western portions of our CWA just a tad bit earlier than the
previous forecast in the form of showers with perhaps a few
rumbles of thunder. Have adjusted the pops/wx to reflect this
earlier arrival time (around 04-05z).

&&

.DISCUSSION...
Issued at 255 PM EDT Thu Jul 10 2025

Several rounds of showers and storms will be possible through the
weekend. Confidence is low to medium in how the pattern evolves in
the next 12-24 hours due to several factors. An MCS will move
through and decay across Iowa and Illinois overnight into early
Friday morning. CAMs are split on how this convection evolves; the
atmosphere should remain capped but it is possible some of this
remnant convection survives and makes it into our area Friday
morning, especially across northwest Indiana and southwest Lower
Michigan. How the morning MCS evolves will influence how the rest of
Friday goes...CAMs try to reinvigorate convection in Illinois along
any remnant outflow boundaries, but exactly where and when
convection will develop remains highly dependent on if/where any
outflows set up. The cap should hold over our area Friday, but I
can`t rule out a few isolated showers or storms tomorrow
afternoon/evening. Because tomorrow`s forecast is of low confidence,
have left PoPs capped at 40% for the morning and 20% for the
afternoon. Subsequent shifts can adjust as needed if confidence were
to increase for a particular timeframe (especially the
afternoon/evening timeframe). SPC did upgrade areas north of US 30
into a Slight Risk (level 2 of 5) for Friday although confidence is
very low in any storms reaching severe criteria, unless storms are
able to develop along a remnant outflow boundary.

Heat and humidity build on Friday into Saturday, setting the
stage for another round of rain/storms over the weekend as a
cold front comes through. Increasing southerly low level flow
and WAA will result in high temperatures in the upper 80s to low
90s and dewpoints in the mid 70s by Saturday, which will lead
to peak heat indices in the mid to upper 90s. A cold front,
aided by a 500 mb shortwave pivoting through, will bring chances
for rain/storms to the area late Saturday afternoon through
Sunday morning. The cap will likely hold until the latter half
of the day, but hot and humid conditions should allow for
destabilization to occur by the afternoon and evening. With
ample instability (2500-3000 J/kg SB CAPE) but unidirectional
flow at the surface and aloft, a few storms may be strong to
severe but widespread severe weather is not expected over the
weekend at this time. Once again, SPC has the area in a Marginal
Risk (level 1 of 5) on Saturday. NAM soundings show inverted v
profiles, which would suggest gusty to damaging winds would be
the main hazard. Signals for heavy rainfall are also there for
Saturday evening into Sunday morning. Given that the heaviest
rain/storms may move through overnight with weak southwest flow
parallel to the front and PWATs around 2", flooding potential
may need to be monitored Saturday night into Sunday. WPC does
have much of our forecast area in a Marginal Risk (level 1 of 4)
for isolated instances of flash flooding on Saturday and
Sunday.

A weakly amplified upper level ridge and surface high pressure build
across the Great Lakes region into early next week, bringing dry
conditions later Sunday through Tuesday. Chances for diurnally
driven showers and storms will persist each day, but chances are
fairly low (20% or less). Hot and humid conditions persist under the
upper level ridge with highs near 90 degrees until midweek.

&&

.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.

&&

$$

UPDATE...
DISCUSSION...Johnson
AVIATION...AGD