875
FXUS63 KIWX 141054
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
654 AM EDT Mon Jul 14 2025

.KEY MESSAGES...

- Patchy dense fog this morning, especially across areas west
  of US Route 31 in northern Indiana and possibly into portions
  of SW Lower Michigan.

- Remaining hot today but less humid. Humidity levels will
  build for Tuesday and Wednesday with afternoon heat indices
  back into the 90s.

- Chances of rain return for later Tuesday, but greatest chances of
  showers and thunderstorms for Wednesday and Thursday.

&&

.DISCUSSION...
Issued at 350 AM EDT Mon Jul 14 2025

A sheared upper level wave from the Lower MS Valley will
continue to depart to the east this morning, allowing axis of
higher PWATS to sink southeast of the local area. Clouds and any
lingering scattered rain showers across the far southeast
should diminish through the mid to late morning hours.
Otherwise, for the near term, the combination of yesterday`s
rainfall, light winds, and partial clearing has led to fog
formation, particularly across southwest locations which
received more rainfall yesterday, and where crossover temps are
running higher. A Dense Fog Advisory was issued earlier this
morning for White/Cass/Fulton/Pulaski IN counties. Satellite
imagery/sfc obs do suggest some of this dense fog may be trying
to shift eastward into southwest portions of Kosciusko County
this morning, with additional patches of dense fog in sfc obs
across far NW IN/SW Lower MI where radiational cooling has been
optimized. May pad the Dense Fog Advisory with an SPS shortly,
but a small areal extension of the Dense Fog advisory may be
needed over the next hour or two.

For the rest of the day, drier low level air should persist across
the bulk of the area with mid/upper level low amplitude ridge
building back across the Great Lakes and Ohio Valley into tonight.
Broad subsidence regime, good deal of sun today, and moderation
of weak low level thermal trough should support above normal
highs today in the mid to upper 80s. Low level flow will also
be very weak today under the influence of a broad sfc
anticyclone. A lake breeze is expected to develop under this
weak flow regime but unseasonably warm southeast Lake Michigan
waters may temper lake breeze penetration/strength.

For Monday night through Tuesday night, attention will turn to
the gradual northeast advance of another vort max in the weak
mid/upper level steering flow across the Lower MS Valley. This
vort max should tend to shear as it begins to encounter slightly
stronger westerlies across the Great Lakes. Shearing nature of
this feature would appear to take best low level moisture
transport from the Ohio River Valley into west central Ohio by
late Tuesday night/early Wednesday. Weak low level southwesterlies
associated with this feature will allow the low level theta-e
gradient displaced just south of the local area to return back
north resulting in increased humidity, particularly by late
Tuesday into Wednesday. Precip chances on Wednesday may be
maximized across NE IN/NW Ohio early in the day as this vort
max lifts northeast. Did consider some downward adjustment to
afternoon PoPs Wednesday given what could be a lull in forcing
between departing sheared vort max, and the onset of a more
active series of eastern Pacific waves later Wednesday into
Thursday. Guidance consensus at this time would suggest best
chance for more organized convection late Wednesday into
Thursday as the upper ridge is temporarily suppressed allowing
stronger frontal forcing to drop into the southern Great Lakes
by this time. There should be plenty of moisture availability in
this synoptic setup so have maintained the ramp up to higher
PoPs again by Thursday PM.

Heat indices will likely reach the mid to possibly upper 90s on
Wednesday, but could be limited by greater cloud cover/precip
chances, particularly east of I-69. Confidence in heat index
forecast decreases post-Wednesday due to potential increased
convective activity. Any associated frontal passages do not appear
to have much opportunity for much southward progress in this pattern
given low amplitude nature. This may place the local area in a
favored instability gradient zone for additional periodic convective
clusters for the weekend into early next week. Given this synoptic
setup, forecast temps near climo seem appropriate for much of the
longer term periods.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 644 AM EDT Mon Jul 14 2025

A weak front extended across northwest Ohio into northeast
Indiana. Fog was becoming more widespread but still had not
formed at either terminal (although SMD was 3SM BR). Continued
to leave fog out of TAFs, although a brief intrusion of fog is
possible before 15Z. Ground fog is likely to be near or in the
vicinity of the terminals, but should lift before 14Z. As for
thunderstorms, the activity has moved well southeast out of the
area. Mid level lapse rates continue to be very stable and
should inhibit deeper convection. A relatively small area of dry
air with slightly lower surface dew points has spread across
northern Indiana behind the front and should help keep storms
from forming today. Otherwise, winds should remain light.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Dense Fog Advisory until 9 AM EDT this morning for INZ013-015-
     020-022.
OH...None.
MI...Air Quality Alert until midnight EDT tonight for MIZ078>081-
     177-277.
MARINE...None.

&&

$$

DISCUSSION...Marsili
AVIATION...Skipper