257
FXUS63 KGRB 022038
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
338 PM CDT Tue Sep 2 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Showers and a few embedded thunderstorms expected tonight into
  Wednesday morning. No severe storms are expected.

- Turning much colder for the mid to late part of the week. Record
  to near-record cold high temperatures remain likely for Thursday
  and possible for Friday. Below normal temperatures to continue
  through the weekend.

- Another round of rain arrives Thursday night and lingers into
  early Friday.

&&

.DISCUSSION...
Issued at 337 PM CDT Tue Sep 2 2025

Precipitation Trends: A well-developed MCV over southwest Lake
Superior will bring an initial band of showers into NC/C WI this
afternoon. MUCAPE is expected to gradually build to 300-700 j/kg
late this afternoon/early evening, so an uptick in shower
activity and a few embedded storms will be possible. Given the
very modest instability and weak deep layer shear (less than 20
kts), do not anticipate any strong to severe storms. These
showers are expected to gradually weaken as they shift east later
this evening, but a strong cold front will bring additional
showers and isolated storms to the western part of the forecast
area late evening, and to the rest of the area overnight. Even as
this frontal precipitation heads east around daybreak, additional
scattered showers will form as a short-wave trough moves through
Wednesday morning. Most of the forecast area dries out by
mid-day Wednesday, but cold northwest flow and additional short-
wave energy brings lake-enhanced rain showers to north central WI
Wednesday afternoon and Wednesday night.

Another strong short-wave and associated low pressure system track
through the region Thursday night into early Friday morning,
bringing widespread shower activity. Much quieter weather returns
for the weekend, with high pressure arriving Saturday night into
Sunday.

Temperatures: A big cool down arrives for the mid to late part of
the week, in the wake of tonight`s cold frontal passage. As has
been advertised for the past few days, record low high temperatures
are likely on Thursday, and possible on Friday. Frost and freeze
potential at night will be mitigated by winds and clouds off Lake
Superior, but a window of opportunity for headlines may emerge at
some point.

.Marine...
Have trimmed back on waterspout potential, limiting the chances to
Wednesday morning, when the cold front moves through. Although
instability will be sufficient Wednesday afternoon and Wednesday
night, an inversion is expected to limit convective cloud
heights, resulting in less potential for those periods. We will
need to monitor the potential Thursday night into early Friday as
a low pressure system tracks through the area

Periods of gusty westerly winds are possible from Wednesday
through Saturday, which may result in hazardous conditions for
boaters at times. Right now, the greatest potential for Small
Craft Advisories would appear to be on Friday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1237 PM CDT Tue Sep 2 2025

Precipitation trends and low ceilings will be the main aviation
concerns for this set of TAFs.

SCT-BKN cumulus clouds had developed early this afternoon. A band
of showers associated with an MCV were gradually weakening as they
approached the forecast area.

Precipitation trends will be tricky, as three separate forcing
mechanisms; the MCV, a strong cold front and a short-wave trough,
move through the region ((at different times) during the TAF
period. The initial weakening band of showers could perk up a bit
as instability slowly builds this afternoon, and this could result
in a few thunderstorms in NC/C WI late this afternoon and early
evening. As this initial activity shifts east and weakens, the
frontal precipitation will arrive later this evening and spread
east through the overnight hours. Additional scattered showers
could develop late tonight into Wednesday morning as a short-wave
moves through. Have attempted to provide some timing of these
features, but this may need to be adjusted a bit.

Ceilings will quickly lower as the cold front moves through
overnight, with most locations lowering to MVFR/IFR. In addition,
there may be some minor vsby restrictions due to showers and fog.
A slow improvement in flight conditions is expected during the
mid to late morning hours on Wednesday, but most places will
probably not reach VFR before 18z/Wed.

Steady but light southwest winds will persist this afternoon and
evening, then become gusty from the west to northwest in the wake
of the frontal passage late tonight into Wednesday morning.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......Kieckbusch