313
FXUS63 KGRB 030329
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1029 PM CDT Tue Sep 2 2025

Updated aviation portion for 06Z TAF 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 06Z TAF Issuance
Issued at 1029 PM CDT Tue Sep 2 2025

One area of showers is exiting far northeast Wisconsin late this
evening. Meanwhile, a more potent line of showers and storms is
progressing southeast over northwest WI at about 25 kts and will
reach RHI at about 05z at its current speed and heading. Some
weakening is expected by the time this line reaches RHI, which
should continue as it moves into northeast WI. Confidence is low
that this line will reach central WI and the Fox Valley.

Another round of showers is expected to moved across the region
between 10-16z Wednesday. This round will likely be more
widespread (60-80% chance). Ceilings will quickly lower as these
showers and associated cold front move through, with most
locations lowering to MVFR/IFR. In addition, there may be some
minor vsby restrictions due to the showers. A slow improvement in
flight conditions is expected during the late morning or early
afternoon hours on Wednesday, but most places will probably not
reach VFR before 18z Wednesday. North- central WI may remain MVFR
through much of the afternoon.

Widely scattered shower activity is expected to redevelop over
central and north-central WI on late Wednesday afternoon as a
potent upper low draws near and end by mid-evening. Clearing is
then expected to arrive from west to east by late evening.

Steady but light southwest winds will persist into the early
overnight, then become gusty from the west to northwest in the
wake of the frontal passage Wednesday morning. Winds will remain
gusty through the rest of the TAF period.

&&

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

&&

$$

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