714
FXUS63 KIWX 301831
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
231 PM EDT Wed Jul 30 2025

.KEY MESSAGES...

- Showers and thunderstorms expected this afternoon into
  Thursday morning. Locally heavy rainfall and flooding the
  primary threat into Thursday morning. A strong storm could
  still cause gusty to damaging winds into the evening.

- Cooler and less humid weather Friday into this weekend.

- Hazardous swim conditions are possible for the beaches of
  LaPorte and Berrien counties starting later today and
  persisting into Saturday. Waves 1 to 3 feet with the
  occasional 4 foot wave possible during this time.

&&

.DISCUSSION...
Issued at 221 PM EDT Wed Jul 30 2025

With an area of surface high pressure to the north in Canada and to
the south of the Gulf and shortwaves rotating around a mid level
ridge over the Southern Plains/Lower Mississippi Valley, we`re
watching thunderstorms for this afternoon and overnight. There are
some model discrepancies with timing and ingredients that play a
role in thunderstorm severity. With a cold front sauntering
southward, those shortwaves will try to set off those thunderstorms
in an environment with 1000 to 3000 J/kg of MUCAPE up to around
10pm. The NAM maintains the instability of the environment during
the afternoon whereas the HRRR and the ECMWF seem to drop it down to
less than 1000 J/kg by 00z. This is as the first squall line and its
cloud shield approaches from the west, this does enough to stunt sfc
instability for thunderstorms. Additionally, with squall lines, it`s
a nice thing to have around 50 kts winds in the low level jet,
however, this weak low level jet only supplies around 30 kts. So
while models are calculating 30 to 40 kts of effective shear,
maintaining a squall line may be difficult. Perhaps getting a few
thunderstorms to sprout out in front of the line is a possibility
especially with lingering outflow boundaries around the area that
could create differential heating zones, but those may be stunted by
the lingering debris clouds from this early afternoon`s squall line
remnants.

Out in front the cold front, there`s also plenty of moisture to work
with. 850 mb dew points are around 15C and sfc dew points are above
70 degrees while PWATs are well above normal at around 2 inches.
There is a little better model consensus on what appears to be a
heavy rain scenario as the southward moving cold front slows down
over the area and shortwaves continue to move through likely 0.5 to
1.5 hour after the severe chances wane. This may allow a training of
storms scenario, but MBE vectors appear to be strong enough to not
allow backbuilding storms and motion appears to be quick enough to
keep rain chances progressive enough. We`ll have to watch and see if
the morning squall line storm track is southeasterly enough to be
able to shunt the moisture axis south of the area and starve us of
better moisture. Over the last 48 hours, most storms have stayed
north of US-30, however, looking back to 7 days, most of the 2 inch
above normal precipitation anomalies appear to reside south of US-
30. 00z HREF/NBM precipitation probabilities and PMM output point to
along and north of US-30 being the main target zone for
precipitation (along the main front). Whereas the RRFS/REFS seems to
point towards more south of MI, which could have some truth behind
it if those outflow boundaries are able to restrict rain to
along/south of them. We still have Cosperville in action stage and
the latest model runs from the RFC indicate NVLI3 may also make a
run at action stage with additional rain from this event. So,
while we have been wet and the atmosphere is conducive to
flooding, the lack of a better low level jet and not enough
confidence in actually observing flooding, have decided to stand
down on a flood watch.

Rain lingers Thursday morning and probably lingers at least in areas
south of US-30/US-24 in the afternoon as well, if not farther north
even, with how slow this front is moving. As the upper low in Canada
sends a vort max towards the fingers of Lower Michigan 18z, this is
probably enough to finally push the front farther south by the end
of the day Thursday. Behind the front, 60 degree dew points are
expected to be observed in Michigan Thursday morning and 50 degree
dew points are expected to be observed on Friday. Additionally, our
warm highs in the 80s and 90s that we`ve had will be much cooler on
Thursday with highs in the 70s and those continue through Saturday.
Given east winds, but with high pressure east of the area on Sunday,
attempts will be made to reach 80 degrees in some spots between
Sunday and the next work week as 14 and 15C at 850 mb straddles
the area. It may take until we to early next week to finally get
our next chance for rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 216 PM EDT Wed Jul 30 2025

Uptick in storms in ne IL associated with MCV over srn WI will
overspread the terminals later this aftn. Additional
showers/storms are likely overnight in response to additional
upper wave disturbance tracking out of NE. Net result is VFR
giving way to MVFR in time.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...Air Quality Alert until midnight EDT Thursday night for
     MIZ078>081-177-277.
MARINE...None.

&&

$$

DISCUSSION...Roller
AVIATION...T