469
FXUS63 KIWX 131029
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
629 AM EDT Sun Jul 13 2025

.KEY MESSAGES...

- Some renewed low chances of showers (20-40%) and a slight
  chance of thunderstorms (10-20%) for later today into tonight,
  mainly along and south of US Route 24.

- Brief relief from higher humidity today into Monday but peak afternoon
  heat indices return into the 90s for Tuesday and Wednesday.

- Some smoke aloft from Canadian wildfires is expected to spread
  across the region today, particularly across the Great Lakes.

- Chances of showers and a few storms return Tuesday, but
  greater chances expected by midweek.

&&

.DISCUSSION...
Issued at 356 AM EDT Sun Jul 13 2025

A couple of weak sfc troughs/cool fronts persist across the
region this morning. The first of these troughs is shifting
across northwest Ohio and far northeast Indiana, roughly
extending from Defiance OH to Marion IN as of 07Z. A few light
showers appear to be trying to develop along this weak
convergence zone. A second reinforcing sfc trough, appearing to
mark more of a low level moisture gradient, is positioned back
across northwest Indiana/SW Lower Michigan. Instability profiles
are more limited with this area of convergence however. Have
kept in "silent" 10 PoPs across NE IN/NW OH for next few hours
as expected coverage will likely be below mentionable levels.

Otherwise today, primarily low level theta-e gradient is
expected to set up across central Indiana and will be watching
the northeast evolution of a mid/upper level trough across
northern Missouri. A portion of this vort max should get
ingested by a broader northern stream trough working across the
Upper Midwest/northern Great Lakes. As this occurs, some renewed
low level moisture transport will work back northward across
the Ohio River Valley and into portions of northern
Indiana/northwest Ohio, especially along and south of the US 24
corridor into this evening. Given shearing nature of the
forcing, forecast confidence was low in the northward extent of
higher chance PoPs later this afternoon into this evening. How
quickly these features phase may dictate northward extent of
mentionable PoPs. However, given this renewed moisture
transport, sheared vorticity lifting across the area, and some
support in right entrance region of larger scale upper jet, did
maintain low-mid range chance PoPs across the south later today
PM into early Monday. A few storms are possible particularly
late afternoon into this evening with some indications in
guidance of 500-1000 J/kg sfc/near sfc based CAPE. Best coverage
may end up being late evening/early overnight, when weak low
level moisture convergence at nose of weak low level jet is
maximized. Otherwise today, some increase in clouds is expected
as low/mid level moisture transport returns, with smoke aloft
from Canadian wildfires shifting across the Great Lakes. An Air
Quality Alert remains in effect for Michigan today through
Monday morning.

Isolated shower potential could persist across the far
south/southeast into early Monday, but otherwise dry conditions
and decreasing clouds are expected in the afternoon as the
sheared positively tilted trough shifts east of the area. Large
scale mid/upper level ridging will build back into the region
Monday night. Guidance is in agreement that another cut off vort
max across the southern Plains will enter this weak steering
flow and slowly lift north to the Mid MS River Valley Tuesday
evening. This should allow a northward return of the richer low
level moisture back into the local area later Tuesday/Tuesday
night. Previous forecast already included low chance PoPs
Tuesday into early Wednesday morning which appears appropriate.
Heat and humidity will be on the increase Tuesday/Wednesday with
some low-mid 90s heat indices possible during this time.

Overall medium range guidance consensus has been consistent with
an active eastern Pacific pattern for midweek, which will
eventually allow longwave ridge to dampen, and another fropa
some time in the late Wednesday/Thursday period. This could
result in more organized convective potential heading into this
period.

The main short wave track will remain across northern tier of
states for Thursday into next weekend, which would conceptually
keep local area in fairly strong baroclinic zone resulting in
some susceptibility to additional shower/storm chances. For
this reason, have accepted the blended guidance broadbrush PoP
inclusion for much of the long term period with difficult in
timing any higher probability chances at this forecast distance.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 611 AM EDT Sun Jul 13 2025

An upstream trof was approaching from the west and was helping
to temporarily build the weak ridging into northern Indiana.
Given weak subsidence and extremely stable mid level lapse rates
near 5C/Km, have kept showers and storms out of TAFs.
Precipitable water values were anomalously high (around 2.0")
and with daytime heating and very weak subsidence these
conditions could allow a stray shower or storm. Otherwise,
winds will be light and conditions VFR. Scattered cumulus is
possible by late afternoon, but should not be operationally
significant.


&&

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

&&

$$

DISCUSSION...Marsili
AVIATION...Skipper