Merrillville, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

615
FXUS63 KLOT 132323
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
623 PM CDT Wed Aug 13 2025

.KEY MESSAGES...

- Uncomfortable heat and humidity returns this weekend with
  heat indices 95 to 105 degrees.

- Shower and storm chances return on Sunday and continue early
  next week.

&&

.DISCUSSION...
Issued at 249 PM CDT Wed Aug 13 2025

Expect primarily dry weather for the remainder of the day, with
only a small chance (15%) for an isolated sprinkle or two in
the vicinity of the lake breeze boundary. This small threat will
end quickly with sunset this evening as the boundary layer
quickly cools and stabilizes. Light winds and mainly clear skies
will allow temperatures to drop back through the 60s tonight,
with even a few mid to upper 50s possible in the typical cool
spots by early Thursday morning. Lingering low-level moisture
may again foster some patchy fog development towards daybreak,
particularly across interior sections of northern IL, back into
and central IL and IN.

Quiet and dry weather will persist through the remainder of the
week as upper-level ridging begins to build back over the Midwest
into the western Great Lakes. The main weather story with this
pattern will be the quick return to hot and increasingly humid
conditions Friday, and especially on Saturday. Temperatures will
be warming back to around 90 on Friday, then into the low to mid
90s on Saturday. These temperatures, in combination with
increasing humidity will yield heat indices into the mid to
upper 90s Friday afternoon, and likely to 100 to 105 by Saturday
afternoon.

These hot and humid conditions look to persist on Sunday.
However, attention will be focused on the evolution of a cold
front shifting southward into the Upper Midwest and Upper Great
Lakes Saturday into early Sunday. With this front likely to become
a focus for strong convection to our north through the weekend,
waves of enhanced storm outflow may act to drive the effective
cold front far enough south to briefly enter northern parts of our
area as early as Sunday afternoon. Confidence on this occurring
remains low at this time. However, if this occurs some heat relief
would be possible along with an increased threat of storms Sunday
afternoon.

The threat of storms will continue early next week (Monday and
Tuesday), though the best chances will likely be tied to the
timing of another cold frontal passage associated with an area of
low pressure expected to track through the Upper Midwest. Due to
continued uncertainty in the finer scale details, we made no
changes to the NBM output, which generally broad brushes 20-30%
chances for storms both days. Conditions are also likely to remain
very warm and humid for a period early next week, though there
are signs that cooler weather will shift into the area behind this
next cold front for the second half of next week.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 623 PM CDT Wed Aug 13 2025

Only forecast concern is fog potential overnight/Thursday
morning outside the Chicago terminals.

A lake breeze will continuing move west until it dissipates with
sunset this evening. Winds will become light and variable for
much of the area tonight. Where directions persist, they will
likely be light north/northwest. Winds will become northeast
Thursday morning and then more easterly with a lake breeze for
the Chicago terminals Thursday afternoon. Further inland, winds
may trend more southeasterly.

Patchy fog is expected overnight into early Thursday morning,
mainly south and west of the Chicago terminals. Confidence is
low for how widespread the fog may become. For now have included
mvfr tempo mention at only RFD. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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