852
FXUS63 KIWX 040112
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
912 PM EDT Thu Jul 3 2025

.KEY MESSAGES...

- Hot and humid Friday through this weekend.

- Better chances (30-50%) for scattered showers and storms
  arrive Sunday afternoon into Sunday night.

&&

.UPDATE...
Issued at 905 PM EDT Thu Jul 3 2025

No major changes to previous forecast anticipated at this time.
A small cluster of showers and storms rode along a residual
outflow boundary from south central Lower Michigan, but these
storms continue to diminish in intensity as they depart far
northwest Ohio. Otherwise, best near sfc convergence in wind
field remains anchored from southern suburbs of Chicago into
portions of LaPorte County where a rogue shower is possible over
the next hour or two as diurnal instability wanes. Otherwise,
expecting a mainly dry forecast for the overnight hours. As main
discussion mentioned, may eventually have to watch for some
residual convective activity to possibly survive into SW Lower
MI/NW Indiana Friday morning. Still a good deal of uncertainty
in this scenario with some indications in near term guidance
that some upwind propagation may be favored across S WI/N IL
late tonight/early Friday that could take favored propagation
south into N IL as opposed to the local area. Inherited slight
chance PoPs by 15Z timeframe Friday still seem appropriate given
these inherent uncertainties in this pattern.

&&

.DISCUSSION...
Issued at 217 PM EDT Thu Jul 3 2025

Convection should be very limited again late this afternoon into
early this evening in the vicinity of a lake shadow/breeze given
limited boundary layer moisture and warm/dry mid-levels. Attention
later tonight into Friday morning will turn to how upstream
convection across WI evolves on the leading edge of a building ~592
dam 500 mb ridge. This activity should struggle to survive east-
southeast as it outpaces its LLJ and associated moisture
transport/convergence. Whether a MCV, cloud debris, or a more robust
outflow boundary folds into portions of our area on Friday
remains uncertain and could hold temperatures down a bit with
non-zero shower/storm chances. At this point, this kind of
impact locally appears less likely (only a 10-20% PoP) with the
upper ridge rather aggressive to build in with dry conditions
and highs making a run at 90F likely for most locations.

Upper ridge axis will be overhead on Saturday with hot and dry
conditions prevailing. This ridge breaks down into Sunday as a
dampening shortwave tracks east into the Great Lakes and forces a
slow moving cold front through Sunday afternoon-night. Pronounced
moisture pooling per ~2" precipitable water values, and moderate
boundary layer destabilization pre-frontal Sunday afternoon, while
overall flow/shear through the column is weak given the shearing
nature to the wave. Similar to previous events, threats appear to
locally heavy rainfall and gusty winds (wet downbursts) with
scattered thunderstorms during this time.

Ensembles continue to support broad upper level troughing across the
Midwest and Great Lakes next week with seasonable temps. Mainly dry
conditions should also win out in this regime, though did retain NBM
low PoPs given the non-zero potential for mainly diurnally driven
showers/storms with any weak embedded mid level impulses, and along
any outflow/lake boundaries.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 753 PM EDT Thu Jul 3 2025

A few showers and thunderstorms developed this afternoon in a
northwest flow regime downstream of an upper ridge axis
extending from the southern Plains into northwest Iowa. Subtle
mid level height rises are underway across much of northern
Indiana as the mid/upper level ridge axis slowly builds in
through the remainder of the night. Most favored area of
isolated shower/storm development through late evening should be
well north and east of the terminals given the mid level height
rises becoming established and residual outflow boundaries
confined mainly to extreme NE Indiana/NW Ohio. Still cannot
rule out a very low end probability of an isolated shower
developing along a lake enhanced trough axis/convergence zone
running from far NW Indiana to the KFWA vicinity through around
02Z, but any shower development will remain very isolated and
short-lived.

Later tonight, a weak low level jet nosing into the
Corn Belt from the southern Plains will likely aid in some
nocturnal convection with some propagation expected into the
Mid MS Valley and potentially far western Great Lakes early
Friday morning as low level jet veers. Downstream airmass
across N Indiana should be less favorable for maintenance of
this convection, but a non-zero chance of showers could develop
after 12Z Friday. However, given increasing influence of
upstream ridging and low confidence in this scenario will carry
dry terminal forecast through the period.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Air Quality Alert until midnight EDT Friday night for INZ020.
OH...None.
MI...Air Quality Alert until midnight EDT Friday night for MIZ177-
     277.
MARINE...None.

&&

$$

UPDATE...Marsili
DISCUSSION...Steinwedel
AVIATION...Marsili