408
FXUS63 KIWX 301021
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
621 AM EDT Sun Aug 30 2026

.KEY MESSAGES...

- Scattered showers are expected today from northwest Indiana
  extending northeast into south central Lower Michigan.
  Isolated thunderstorms are possible, but severe weather is not
  expected.

- Heat and humidity will build early this week with peak
  afternoon heat indices expected to reach around 100 for
  Tuesday and Wednesday afternoons.

- Slightly better chances for showers and thunderstorms (20-40%)
  arrive for the second half of the upcoming week.

&&

.DISCUSSION...
Issued at 330 AM EDT Sun Aug 30 2026

Scattered showers continue to develop this morning from northern
Illinois extending east across southern Lake Michigan into much of
central Lower Michigan. This showers are developing along an axis of
strengthening low/mid level theta-e advection and coincident
with strengthening isentropic upglide. Some respectable
elevated moisture advection should provide some 100-300 J/kg
MUCAPEs in a relatively narrow axis from northern Illinois into
central Lower Michigan this morning where moisture transport
appears to be maximized this morning. A subtle, weak mid level
short wave also appears to be kicking out of northeast
Iowa/southeast Minnesota which should further enhance isentropic
forcing closer to 12Z this morning. Will maintain an isolated
thunder mention and scattered rain shower PoPs across these
locations. Outside of this narrow MUCAPE axis, low level
moisture transport is somewhat more limited across the remainder
of the forecast area, so some question as to southeast extent
of isolated thunder potential and higher PoPs. Otherwise, warm
advection today should promote warmer conditions with highs in
the lower to middle 80s. Scattered showers/cloud cover do make
this a below normal confidence temperature forecast today for
northwest half of the area where showers should be more
numerous.

By later this afternoon into this evening guidance generally agrees
that stronger isentropic lift in the 310-315k layer should become
focused across northwest Ohio and approaching the eastern Great
Lakes, with another zone of stronger advective forcing taking shape
from SE MN into southwest WI as a low level jet refocuses. It is
possible some low PoPs will need to be extended through tonight
across northern locations, but given this weakening trend in
advective forcing will keep PoPs below mentionable levels for most
areas.

For late tonight into Monday, mid level ridge axis will shift across
the southern Great Lakes allowing more pronounced mid level WAA and
warm 700 mb temps of +10 to +14 deg C to overspread local area.
It is possible some isoalted showers/storms could develop at
the nose of this stronger mid level WAA but confidence is low
given lack of deeper mid/upper level forcing. Heat concerns
start to increase for Monday due to the persistent low level
warm/moist advection with peak afternoon heat indices expected
to reach the mid 90s.

By late Monday night into Tuesday low level flow is expected to veer
more west-southwest as longwave upper ridging gets somewhat
dampened by larger scale upper low across US/Canadian border.
This westerly flow regime will allow low level theta-e ridge to
the west to become more firmly entrenched locally and may
result in heat indices around 100 degrees both Tuesday and
Wednesday afternoons. An associated cold front with the southern
Canadian negative height anomaly is expected to drop across the
southern Great Lakes late Wed into Thu. A conservative approach
to PoPs still seems in order for late Wednesday given stronger
dynamic forcing should be located well to the north of the local
area and likely persistence of warm mid level thermal profiles
and possible moderate surface based CIN.

Medium range guidance still suggests a transition to more
amplification of longwave pattern late this work week into next
weekend with position of mean upper ridge axis across central
CONUS. This should prevent additional significant heat concerns
but would likely result in episodes of higher PoPs as some
northwest flow waves interact with a potential instability
gradient across the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 618 AM EDT Sun Aug 30 2026

A veering low level jet and accompanying strong elevated warm/moist
advection will continue to allow for scattered shower
development this morning. An upstream upper speed max and a
weak, subtle mid level short wave ejecting out of the Corn Belt
will allow for continued strengthening of isentropic lift
across northern Illinois/southern Great Lakes over the next
several hours. This advective forcing should result in greatest
coverage of rain showers at KSBN from mid morning through mid
afternoon, with a period of rain showers also expected to affect
KFWA again this afternoon. Stronger low level moisture
transport is expected to remain confined along an axis from
north central IL into central Lower MI today which should keep
most pronounced moisture axis and greatest potential of isolated
thunder just west to northwest of KSBN. It is possible some
thunder mention may be needed at KSBN given weak elevated CAPE
however. Coverage of rain showers should diminish later this
afternoon but a refocusing of low level jet across northern
Illinois this evening could allow for some more showers to spill
into northern Indiana tonight. Otherwise, westward displacement
of stronger low level moisture transport today should allow for
continuation of VFR conditions with primarily mid level cigs
through the period.

&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...Marsili