Merrillville, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

116
FXUS63 KLOT 150813
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
313 AM CDT Wed Oct 15 2025

.KEY MESSAGES...

- Some scattered showers expected this morning, mainly north of
  I-80.

- A period of showers and possible thunderstorms expected late
  Friday night or Saturday.

&&

.DISCUSSION...
Issued at 313 AM CDT Wed Oct 15 2025

Scattered showers are ongoing across southern WI southward into
portions of northern IL early this morning. This is occurring
within a rather broad region of isentropic upglide to the north
of a surface frontal boundary draped across the lower Missouri
Valley eastward through the Ohio Valley. This activity continues
this morning, at least on a widely scattered basis across
northern and northeastern parts of IL and northwest IN. Then, as
we head into the afternoon, any lingering shower activity will
become more isolated in nature, and likely focused more to our
northwest.

Outside of the shower chances, temperatures will be notably
cooler today, owing to persistent cloud cover and an overall
cooler low-level airmass advecting into the area on northeast
winds. Accordingly, temperatures are unlikely to warm much above
the low 60s today, save for areas well south of I-80, where
some mid to upper 60s are possible.

The weather pattern will turn more active across the central
CONUS later this week and especially this weekend. While there
continues to be uncertainties with the smaller scale details of
this pattern, particularly with regards to the exact timing of
precipitation, more frequent rain chances and some typical
autumnal temperature swings can be expected into next week.

The primarily driver of this active weekend weather is a long
wave closed off mid/upper trough currently residing across the
west coast. Model and ensemble guidance all support a
significant impulse ejecting northeastward from the base of the
trough and setting the stage for lee cyclogenesis and a
northward moving surface cyclone into the northern Plains and
southern Canada Thursday into Friday. As this occurs, a large
and expansive warm sector east of this strong cyclone will
foster a southerly feed of warmer air into our region, thus
supporting a rather quick recovery in temperatures for the end
of the week. As a result, we will see temperatures back into the
upper 60s near the lake, and into the low to mid 70s across
interior sections of IL on Thursday. Thereafter, mid to upper
70s are slatted for Friday, albeit with breezy south winds.
While we cannot totally rule out the possibility for a few warm
air advection driven showers or storms Thursday night into
Friday as the surface warm front approaches, it appears much of
the more widespread precipitation chances will hold off until
sometime late Friday night or Saturday as the systems cold front
begins to shift towards the area.

Over the past 24 hours, the main change in the guidance for
this weekend has been a trend towards a slower cold frontal
timing (later Saturday), and an associated trend towards the
development of another surface low along the surface cold front
in our area Saturday afternoon and evening. This secondary
surface low development appears to be tied to another impulse
emanating from the Gulf of Alaska, that digs southeastward into
the central CONUS along the western periphery of the larger
scale trough. At this time, confidence in the details with this
possibility remain low at this time, owing to the complex
interactions that are likely to occur with the individual
systems over the next few days and are difficult for the models
to handle at this timescale. Nevertheless, we will have to keep
an eye on this period, as showers and thunderstorms look likely,
and a slower evolution could result in some heavier rainfall
potential.

As the trough and accompanying cold front finally move across
the area expect a much cooler (though fairly seasonable) air
mass to filter into the area early next week.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1230 AM CDT Wed Oct 15 2025

Forecast concerns include...

Scattered showers through late morning.
Gusty northeast winds early this morning.
Possible mvfr cigs mid morning to mid afternoon.

Scattered, mainly vfr showers are expected through the overnight
hours. Eventually, toward daybreak, the shower coverage may
increase with brief mvfr visibilities possible. These showers
will slowly dissipate through the mid/late morning with vicinity
mention still looking reasonable through midday. Cigs are
expected to remain generally vfr through daybreak and then there
is some guidance showing the potential for mvfr cigs later this
morning into early this afternoon, especially across far
northern IL. Confidence is low for prevailing mvfr cigs and have
maintained scattered mention for now. Low vfr cigs will likely
continue into this evening and then are expected to scatter out
into early Thursday morning.

Northeast winds will continue through this evening with gusts
into the 15-20kt range through daybreak this morning. Winds will
turn more easterly tonight into early Thursday morning with
speeds becoming light. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CDT this morning for the IN
     nearshore waters.

&&

$$

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