Merrillville, Indiana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

876
FXUS63 KLOT 250520
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
Issued by National Weather Service Lincoln IL
1220 AM CDT Fri Apr 25 2025

.KEY MESSAGES...

- A Lake Breeze will continue to push inland late this afternoon
  and evening. Temperatures in the 70s/80s will fall through
  the 60s behind the boundary with 50s near the lake front.

- Scattered showers & storms (30-40%) will move across northern
  Illinois and northwest Indiana late this evening and overnight.
  Additional showers and storms are likely (60-90%) Friday.
  Severe weather is not anticipated at this time.

- A cold front will move across the region early next week that
  will be capable of producing strong to severe thunderstorms.
  There is a 15% risk of severe weather west of a Ottawa to
  Waukegan line Monday and Monday night, and to the east on
  Tuesday.

&&

.UPDATE...
Issued at 857 PM CDT Thu Apr 24 2025

Updates made for showers drifting a bit farther northeast than
expected so far this evening and moving into portions of
northwest/north-central IL ahead of an approaching
shortwave. These should should continue to spread slowly
eastward overnight. Otherwise, forecast is on track with lows in
the upper 40s and 50s, and diminishing northeast winds.

37

&&

.DISCUSSION...
Issued at 156 PM CDT Thu Apr 24 2025

REST OF TODAY...
This afternoon, an ill-defined warm front and a baggy pressure
gradient are in place across southern Iowa into northern
Illinois. Weak flow near the frontal trough has allowed a lake
breeze to form and push inland. Temperatures well into the 70s
and lower 80s will be replaced by temperatures in the 60s and
50s immediately near the lake as the lake cooled air spills
inland. Meanwhile, a shortwave trough lifting across the mid
Missouri Valley this afternoon is kicking off showers and storms
to our west. These showers and storms are expected to move
across northern Illinois and northwest Indiana late this evening
and overnight, some of which may develop along the remnants of
the lake breeze boundary as it settles over portions of east
central Illinois and northwest Indiana. Instability will be weak
with MLCAPE values less than 200 J/kg while suboptimal deep
layer shear of 20-25kt will not support severe storms.

FRIDAY...
Surface low will lift from southern Wisconsin Friday morning to
northern lower Michigan Friday afternoon with a trailing cold
front sweeping across northern Illinois and northwest Indiana
through the day. Favored low level trajectories from an open
Gulf will help push dew points up into the 60s for most of the
area Friday afternoon and will contribute to modest
destabilization Friday afternoon as MLCAPE values increase to
near 1000 J/kg. Deep layer shear will remain weak, however,
keeping the severe risk quite low. HREF LPMM indicates a few
isolated swaths of 0.75-1.00 inches of rain will be possible
with the heaviest showers and storms through HREF mean values
are only around a quarter inch QPF through Friday evening.

THIS WEEKEND...
High pressure will translate east across the Great Lakes over
the weekend. North to northeast flow ahead of the ridge axis
Saturday will result in a cool down across the region
particularly near the lake where onshore winds through the day
will result in temps struggling to reach the 50 degree mark.
Further inland temps will warm into the 50s to lower 60s under
sunny skies. Winds turn southeasterly behind the ridge axis
Sunday which will help temps to recover back into the upper 60s
to lower 70s except for the Illinois shores of Lake Michigan
where an onshore component to the winds will keep temps in the
50s near the lake.

NEXT WEEK...
Upper level pattern is progged to gradually amplify over the
weekend with a deep trough setting up over the Great Plains by
early next week. A deepening surface low is progged to lift from
the central/northern Great Plains into the Upper Midwest Monday
then to northern Quebec by Tuesday with a trailing cold front
moving across Illinois and Indiana. Warm air advection will
ramp up in response ahead of the low pushing temperatures for
much of the area including the lake shore into the 80s. More
summer- like dew points well into the 60s will accompany the
warmth and set the stage for moderately strong instability for
portions of the area both Monday and Tuesday. GFS indicates that
around 1500 to possibly 2000 J/kg MLCAPE will be in place
Monday across western portions of the state. The instability
axis will shift to east central Illinois and northwest Indiana
Tuesday. Meanwhile, a jet streak lifting through the lee side of
the deep upper trough will contribute to moderate deep layer
shear around 40 kt Monday and slightly stronger on Tuesday near
45-50kt. LREF joint probabilities for SBCAPE greater than 500
J/kg and bulk shear greater than 30 kt continue to creep up with
70-80% likelihood Monday (highest in the west) and similar
probabilities Tuesday (highest in the southeast). These
parameters are more than sufficient to support a severe weather
threat with passage of the cold front early next week, and this
period will need to be monitored as the forecast details
continue to come into better focus over the next few days.

Deubelbeiss / NWS Lincoln

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1207 AM CDT Fri Apr 25 2025

Persistent north/northeast flow will gradually result in
lowering ceilings Friday morning, with ensemble guidance
suggesting MVFR conditions at KRFD as early as 17-18Z. Chicago-
area terminals more likely to see this develop toward 22-23Z.
Concern remains with potential for IFR ceilings at KORD/KMDW
spreading in off the lake in the evening, with HREF guidance
projecting the probability around 50% and HRRR with the low
ceilings very close by. Will keep the forecast at low MVFR for
now and evaluate it a little further over the next few hours.

Much of the convective concerns from earlier forecasts look to
be setting up south of the TAF sites (though not too far from
KGYY), and thunder chances have been removed from the forecast.

Geelhart


&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 4 PM this afternoon to 7 PM CDT
     Saturday for the IL and IN nearshore waters.

&&

$$

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