120
FXUS63 KIWX 111806
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
206 PM EDT Mon Aug 11 2025

.KEY MESSAGES...

- There is a Moderate Swim Risk for Lake Michigan beaches in
  Berrien County today.

- Remaining hot and humid into Tuesday.

- There are low chances (20-30%) for showers and storms this
  afternoon into Tuesday morning, mainly north of US 24.

- Better chances (50-70%) for showers and storms arrive mid
  afternoon Tuesday through Tuesday evening. Any storms will
  carry a threat for locally heavy rainfall and gusty winds.

- Heat and humidity returns this weekend with peak afternoon
  heat indices well into the 90s.

&&

.DISCUSSION...
Issued at 206 PM EDT Mon Aug 11 2025

Muggy southwesterly flow will persist through at least Tuesday
evening in advance of a frontal zone draped from the Western Great
Lakes to the Southern Plains. A leftover moisture axis and subtle
convergence zone from a shortwave now exiting the northern Great
Lakes may be the focus for isolated showers/storms this afternoon
into early this evening, best chances (20-30%) along and north of
the US 24 corridor. Brief downpours will accompany more robust
showers.

Another convectively induced shortwave likely lifts north-northeast
through IA, northwest IL and WI tonight into Tuesday morning. Shot
of warm/moist advection on its eastern flank, within a developing 20-
30 kt low level jet, may allow convection to clip our northwest IN
and southwest MI zones, best chances (20-40%) later tonight.

The best opportunity for showers and storms (50-70%) will arrive mid
afternoon Tuesday into Tuesday evening as the upstream frontal zone
finally gets a push east in response to an upper trough releasing
east through the Upper Midwest and Great Lakes. A moist and unstable
airmass will be in place with embedded convectively induced impulses
along and in advance of the frontal boundary ultimately determining
the coverage and timing of convection through the area. These
details remain a little hazy at this range as models tend to
struggle in resolving these smaller scale waves. Deep moisture and
potential for training suggests the potential  for locally heavy
rainfall and flooding, with gusts up to 40 mph possible in stronger
water loaded cores.

Cold front may get hung up near the US 24 corridor on Wednesday with
lingering humidity and low chances (20-30%) for renewed convection
if the boundary layer sufficiently recovers. A break from the heat
and humidity remains on track post-frontal into Thursday and Friday.
This will unfortunately be brief as subtropical ridging returns this
weekend with highs back near 90F.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 126 PM EDT Mon Aug 11 2025

Remnant outflow boundaries and weak areas of vorticity moved through
our northwestern areas this morning and there is some chance of an
eastward push of this forcing for the afternoon. Hi-Res models did
not catch onto morning convection within advancement of higher theta-
e airmass that caused weak showers and storms, but these did die on
our western edge of the forecast area. Within weak area of
instability, there could be growth to this area, but extent of
upscale growth is uncertain in any direction especially given extent
of ridging overhead and lingering dry air from recent extended
period of dry air. Warm advection precip appears to be creating MVFR
flight conditions underneath it, but still, it`s uncertain if that
ends up hitting SBN or FWA. At this point, feel it`s most prudent to
keep groups for this out of the TAFs until something allows for more
confidence. Amendments will likely be necessary. Another area of
rain and perhaps some thunderstorms arrives between 00z and 06z as
theta-e axis slides northward. This could provide another
opportunity for lower flight conditions given coverage of rain and
possible intensity of showers/storms, but it`s uncertain if it will
hit SBN or stay north of it. Feel it is most prudent to use PROB30
group for that. Moist axis then advances eastward later Tuesday
night into Wednesday morning which still provides more opportunities
for rain at SBN. However, flight conditions do not appear to be
affected in a prevailing threat and don`t have enough confidence
given model uncertainty to put this threat in either. Still expect
southwest wind trajectories with periods of around 10 kts sustained
during peak heating times.

&&

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

&&

$$

DISCUSSION...Steinwedel
AVIATION...Roller