Lake Station, Indiana Weather Forecast Discussion

246
FXUS63 KLOT 230749
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
249 AM CDT Tue Sep 23 2025
.KEY MESSAGES...
- Scattered showers and some storms possible this afternoon.
  Additional areas of showers and embedded storms tonight, but
  the greatest potential currently looks to focus mainly south
  of the forecast area.
- Intermittent showers may linger across the region Wednesday
  and overnight, but a trend towards drier conditions is
  expected through the end of the week and upcoming weekend.
&&
.DISCUSSION...
Issued at 249 AM CDT Tue Sep 23 2025
Through early this morning: ongoing disorganized convective
clusters currently across McHenry/Lake counties in northeast
Illinois, and any additional spotty convection that develops
along incoming outflows should gradually weaken and diminish
through daybreak. In an unperturbed environment, fog development
appears likely given weak near-surface flow and low/minimal
dewpoint depressions. However, the presence the aforementioned
outflows/gravity waves and debris cloud cover may end up
shunting the greatest fog threat south and east of the region.
At the current time, the main fog corridor looks to be east of
about a Gibson City to Valparaiso line. If the cirrus canopy
diminishes across northern Illinois, the fog threat would
increase commensurately there as well.
Things looks generally quiet this morning. The one exception
might be along and lingering outflow which may continue pushing
east towards the I-57/65 corridors. Additionally, this may serve
as a mesoscale focus for isolated/widely scattered midday and
afternoon convection.
This afternoon and evening, a cold front will shift south out of
Wisconsin and down the lake. Dewpoints ahead of this boundary
are forecast to remain in the low to mid 60s, with temperatures
slated to rise through the upper 70s/near 80 degrees (assuming
ongoing convective debris cloud cover thins through the
morning). Forecast soundings reveal minimal inhibition to
surface-based parcels with a fairly deep (~200 mb) thick low-
level moist layer in place. Interestingly, most model guidance
fails to convect along this convergent axis, potentially owing
to lingering subsidence in the wake of the ongoing convection
and generally limited large scale forcing mechanisms upstairs.
Still, given the progged instability, elected to maintain 30-40
percent chances for showers/storms along the southward-advancing
boundary this afternoon (the ECMWF in particular depicts quite
a bit more coverage of afternoon convection). Finally, while 0-6
km shear is forecast to remain under 20-25 kts (owing to weak
500 mb flow), winds will increase towards 400 mb as a jet streak
intensifies overhead. Based on forecast parcel profiles and ELs
generally under 10 km, this flow should remain immaterial
today, but if warmer temperatures/more instability is realized,
we`d need to keep an eye on the threat for some stronger and
more organized cores.
This evening and overnight, forcing will increase atop the
near-surface frontal zone. This should lead to a general
increase in the coverage of showers and embedded thunderstorms.
As has been the case in this stretch, continue to see
significant run-to-run changes in the handling of the pertinent
larger scale features. A recent signal additionally shows a
compact and potentially fairly deep surface low developing
tonight into early Wednesday morning across downstate Illinois
into southern Indiana. Latest ensemble output indicates this
potential low track remaining south of the region, which would
tend to focus the greatest precipitation chances across central
Illinois and Indiana. Based on all of this, ended up confining
the highest PoPs (low-end likelies) mainly well south of the
Kankakee River. If a solution like the current 00z NAM, UKMET,
ECMWF materializes, a locally heavy rain threat could be
realized immediately to the north of the surface low track into
early Wednesday morning as a coupled upper jet interacts with a
compact zone of low-mid level convergence/f-gen. Presently, the
most concerning signal for this remains just south of the
forecast area.
Carlaw
Our region will be solidly post-frontal on Wednesday, with
breezy north to northeast winds in place. Aloft, several
shortwaves will transit the region, embedded within broad
cyclonic flow in place across the Great Lakes. The broad forcing
generated by these features in combination with ample moisture
will allow scattered showers and perhaps a few thunderstorms to
persist through the day on Wednesday with the highest coverage
(30-40%) focused generally of I-80/east of I-55. While the
highest rain chances will gradually shift southward with the
cold front Wednesday night, the cooler air associated with the
upper-low over the Great Lakes does look to develop some modest
lake induced instability. Thus allowing some lake effect showers
(and perhaps a storm or two) to linger into Thursday along the
northeast IL and northwest IN shores before the low pivots east
of the area Thursday night.
Temperatures on Wednesday and Thursday are forecast to be the
coolest of the week due to the expected cloud cover and
lingering rain chances. Therefore, expect highs during this
period to top out in the low to mid-70s areawide with lows in
the lower to mid-50s.
Heading into Friday, upper ridging is forecast to develop back
into the Great Lakes region which will set up another period of
dry and above average temperatures to close out September. While
another cold front is forecast to dive through our area on
Saturday/Sunday, the cold air reservoir behind the front does
not appear to be sufficient enough to alter temperatures
significantly, except perhaps near the lake. Thus highs should
remain in the upper 70s to lower 80s through the weekend with
overnight lows in the mid-50s. However, conditions will become
more favorable for daily lake breezes towards the later half of
the weekend which should keep temperatures cooler (low to
mid-70s) at the lakeshore.
Yack/Carlaw
&&
.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1236 AM CDT Tue Sep 23 2025
Key Aviation Messages for the current TAF period:
- Scattered thunderstorms through 10Z with a brief window of
  breezy northwest winds.
- West-southwest winds switch to the northeast tomorrow
  afternoon
- Chances for showers late in the TAF period, though better
  coverage expected to the south in Central Illinois
- Potential for MVFR cigs developing tomorrow evening
A broken line of thunderstorms in southern Wisconsin is slowly
sinking southward into northern Illinois. Racing out ahead of it
is a gust front that will switch the winds to the northwest with
gusts up to 25 knots. Behind that wind gust will be chances for
thunder to pass by the Chicago terminals. There`s lower
confidence in how far south the thunder develops if the outflow
races out ahead of it, so it was decided to keep only -SHRA
mentioned in the KGYY TAF. Most thunder should have passed
terminals by around 10Z, though there is a chance for lingering
showers to fester through daybreak.
Behind the showers and storms, winds will weaken but gradually
return to the west-southwest. They will increase to around 10
knots through the early afternoon. As a cold front moves south
out of Wisconsin and is reinforced by a lake breeze, winds will
switch around to the northeast but remain around 10 knots.
Stratus will move down behind the front with increasing chances
for MVFR cigs into Tuesday evening.
With northeast winds meeting southwest winds, there will likely
be a convergent axis that develops late tomorrow where new
showers and storms can bloom. Confidence in where that axis
will develop is low, though models are showing decent agreement
in it developing after 00Z and closer to Central Illinois. There
is a chance that showers crop up in the afternoon, but kept the
TAFs dry at this range. With lower confidence in exact location
and timing, MVFR VCSH was added at the end of the TAF, with a
TEMPO at KGYY being closer to the convergent axis.
DK
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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NWS LOT Office Area Forecast Discussion