226
FXUS63 KLOT 280815
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
315 AM CDT Thu Aug 28 2025

.KEY MESSAGES...

- Widely scattered showers and a isolated T-storms will end this
  morning, before another round this afternoon.

- Another period of dangerous rip currents and swimming
  conditions expected for Lake Michigan beaches late Thursday
  into Friday morning.

&&

.DISCUSSION...
Issued at 315 AM CDT Thu Aug 28 2025

Through Friday:

Scattered showers and a couple of isolated thunderstorms are
moving across the area early this morning in response shortwave
trough combined with warm air advection associated with a
modest westerly low level jet. This activity is expected to push
east of our CWA early this morning with a break in the precip
mid-late morning into the early afternoon along with some
partial clearing.

Cold front currently over the Upper Great Lakes will continue
pushing south into our northern CWA and near the lake early this
afternoon, likely clearing our southern CWA by early this
evening. The break in the precip and clearing should allow temps
to warm into the 70s ahead of the front midday, though temps
will fall a bit in the wake of the front, particularly closer
to the lake. Well inland, where the front isn`t expected to
arrive until late this afternoon or early this evening, highs
should be able to make a run at 80 degrees.

Dewpoints across the region early this morning are mostly in the
upper 50s with some lower 60s over eastern IA. Guidance is in
good agreement depicting an axis of dewpoints in the lower 60s,
if not mid 60s, pooling ahead of the front today. Mid level
temps are unseasonably cold, generally -13C to -15C, especially
across our eastern CWA. These cold mid level temps juxtaposed
over top the 60F+ dewpoints should result in SBCAPE of 500-1000
J/kg ahead of the front. Forecast wind shear profiles are
actually quite favorable for severe weather this afternoon,
with long straight hodographs. If any sustained deep convection
does occur this afternoon, wouldn`t be surprising to see some
supercellular structures and perhaps even a threat of some hail.
This would be contingent on there being thunderstorms this
afternoon and there are some limiting factors to discuss...

The biggest limiting factor today is the depth of the forcing
which will be pretty shallow with the cold front. In fact, the
primary 500mb shortwave trough axis is progged to pass south of
the area prior to the sfc cold front. Forecast soundings aren`t
showing much subsidence in the wake of the mid level trough,
but it is possible that there could be a "CAPE robber"
subsidence inversion ahead of the front even though guidance
isn`t depicting one. Even without that, the cold front will be
fairly shallow and likely moving at a good clip, so the front
may struggle to push parcels to the LFC or result in updrafts
quickly being undercut by the front. Given these limiting
factors, not planning to advertise any type of concerning
convective threat today, but today is one of those days to
monitor trends for the potential for a sneaky mini-supercell
threat with any sustained thunderstorms that do develop.

Brisk northerly winds down the full fetch of the lake will
resulting in building waves and hazardous swim conditions
developing again later this afternoon and continuing into at
least Friday morning. Current beach hazard statement runs
through late Friday afternoon, which could be a bit on the long
side, but not uncommon for waves to hold on longer than
forecast, so no changes planned going headlines.

- Izzi


Friday Night through Wednesday:

High pressure will remain nearly stationary across the eastern
Great Lakes over the weekend. This will allow for dry conditions
for the local area with a slow warming trend back toward normal
temps, though they`ll likely still be a few degrees below
normal. The dry conditions are likely to continue Monday into
Tuesday though there is a bit more uncertainty by Tuesday and
especially Tuesday night as a large upper trough and strong
cold front is expected to move across the area midweek. This
will bring the next chance of showers and perhaps a few
thunderstorms. Another cool airmass is than expected to settle
across the region for the end of next week. cms

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1233 AM CDT Thu Aug 28 2025

Forecast concerns include...

Scattered showers/chance of thunderstorms early this morning.
Wind shift to northeast early this afternoon.
Chance of showers this afternoon.
Possible mvfr cigs this afternoon/evening.

Showers continue to develop across northwest IL and southwest WI
early this morning and these will develop further and spread
southeast across the terminals early this morning. There will
remain the potential for a few thunderstorms through daybreak
and prob thunder mention remains on track. A few lingering
showers may continue through mid/late morning, but the bulk of
the precip is expected to be southeast of the area by mid/late
morning. A cold front will move across the area this afternoon
and there is a low chance for showers with this front and have
include prob mention with this forecast. There is small chance
for an isolated thunderstorm this afternoon but confidence is
too low for mention at this time.

Southwest winds under 10kt will become more westerly after
daybreak, shift north/northwest ahead of the front and then to
the northeast as the cold front moves across the area. Still
some minor timing differences among guidance but in general, the
timing appears to be 18z-19z for ORD/MDW and maintained the
previous 19z timing until the front emerges later this morning.
Northeast winds 10-15kt behind the front will continue into
early this evening with speeds diminishing under 10kt mid/late
evening.

Generally vfr cigs are expected until this afternoon and then a
period of mvfr cigs is possible from mid afternoon through mid
evening, mainly for the Chicago terminals with northeast wind
off the lake. Only medium confidence and for now have maintained
few/sct mvfr level cloud mention. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from this afternoon through Friday
     afternoon for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement from this afternoon through Friday
     afternoon for INZ001-INZ002.

LM...Small Craft Advisory from 4 PM this afternoon to 1 PM CDT
     Friday for the IL nearshore waters.

     Small Craft Advisory from 4 PM this afternoon to 10 AM CDT
     Friday for the IN nearshore waters.

&&

$$

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