103
FXUS63 KLOT 162339
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
639 PM CDT Thu Oct 16 2025

.KEY MESSAGES...

- Periods of showers and possible thunderstorms expected late
  Friday night through Sunday morning.

- Windy and much cooler Sunday.

- Another period of rain possible towards the middle of next
  week.

&&

.DISCUSSION...
Issued at 308 PM CDT Thu Oct 16 2025

Through Friday:

A surface high continues to reside over the Great Lakes this
afternoon which has maintained a warm and partly sunny day for
us. However, there has been an area of showers moving across
northeast IA and southern WI associated with a plume of warm
advection and mid-level moisture. While these showers are
expected to meander across south-central WI this evening and
overnight, some modest moisture may ooze into far northern and
northeast IL and result in a brief period of light showers
and/or sprinkles this evening and overnight. For now have opted
to maintain the 20% POPs for areas near the IL-WI line and near
the IL lake shore but suspect most will remain dry.

The surface high and the associated mid-level ridge will begin
to get pushed eastward on Friday as the broad trough currently
over the Rockies ejects into the Midwest. Though, the lingering
subsidence will support one more dry and warm afternoon for us
with highs forecast to top out in the mid to upper 70s areawide
(some spots could even tag 80 near I-39). Winds will be breezy
however, as the tightening pressure gradient generates some
20-25 mph gusts Friday afternoon.

Friday night through Thursday:

The weather will turn more active as we head into the weekend
as the aforementioned broad trough continues to move east and
phase with a secondary shortwave (currently off the coast of the
Pacific Northwest) on Saturday. At the same time, a cold front
is expected to be draped from the northern Great Lakes to the
south-central Plains and begin to get pushed east by the trough
Friday night. Locally the front should begin to arrive after
midnight Friday night and then slowly meander across northern IL
and northwest IN on Saturday. Therefore, showers and perhaps
even a few thunderstorms are expected to develop across the area
Friday night through Saturday. While forecast soundings
continue to show very limited instability present on Saturday
(around 300-500 J/kg), the strong forcing with the front and
trough in addition to the 35-45 kts of effective shear may be
sufficient to support a stronger storm or two mainly across
eastern IL and northwest IN Saturday afternoon/evening where the
greatest instability is forecast. If a stronger storm does
materialize it seems the main threat would be gusty winds, but
there is some indication that perhaps an isolated spin-up could
occur. That said, the Storm Prediction Center does have portions
of our south and southeast CWA in a marginal (level 1 of 5)
risk for Saturday but given the limited instability still think
the severe threat is rather low at this time.

Heading into Saturday night, a surface low is forecast to
develop somewhere in the Great Lakes region as the phasing
trough pivots into the region. Initially it looked as if this
developing surface low would occur over northeast IL and
northwest IN, but guidance has trended away from that solution
and now has the low forming over WI and Lower MI. While the
overall result from the surface low will be more or less the
same for our area (continuing rain chances Saturday night into
Sunday morning), the low track will ultimately dictate where the
heaviest rainfall axis occurs and how strong the winds are.
That said, guidance remains in fairly good agreement that
northern IL and northwest IN should see around an inch or so of
rainfall in total (from Friday night through Sunday morning)
with some spots possibly picking up close to 2 inches if they
get under the heavier axis. Since these rain amounts should fall
over a 36-48 hour period the risk for flooding appears lows
especially given the antecedent dry conditions. Though, if a
stronger storm trains over an area than some localized ponding
could be seen. In addition to the rain, winds will become gusty
on Sunday as the low deepens with gusts in the 30-35 mph range
likely and localized gusts near 40 mph a possibility if the
deeper low solutions verify.

The low and associated trough are forecast to pivot east of the
area Sunday afternoon which should allow drier conditions to
close out the weekend and kick off next week. Though,
temperatures behind this system will be more typical for late
October with highs in the upper 50s to lower 60s forecast for
Sunday and low to mid-60s for Monday. Another storm system looks
to pivot through the area during the Monday night into
Wednesday time frame but uncertainty remains as to how strong
the system will be and its exact track. For now have maintained
the 20-40% POPs offered by the NBM but suspect further
refinement will be needed over the coming days. Regardless, it
does look as if more seasonable October temperatures will
persist through much of next week.

Yack

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 639 PM CDT Thu Oct 16 2025

VFR conditions are forecast through the TAF period.

ESE winds will gradually turn SSE through the evening remaining
generally light (around 5-10 kt). Winds are then expected to
continue veering to the SSW Friday morning, though confidence
on the exact timing remains on the lower-end and could occur as
early as 12-13Z. Opted to hang on to the inherited 14Z timing
for now. Winds will then steadily increase through the rest of
the morning hours with gusts in the lower 20kt range expected by
the afternoon.

Petr

&&

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

&&

$$

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