994
FXUS63 KGRB 022305
AFDGRB

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

Updated aviation portion for 00Z 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 00Z TAF Issuance
Issued at 605 PM CDT Tue Sep 2 2025

Precipitation trends and low ceilings continue to be the main
aviation concerns for the 00z TAFS.

Multiple rounds of showers are expected over the next 24 hours,
beginning early this evening across north-central WI as an MCV
tracks across the western Upper Peninsula. Showers will likely
remain more scattered or widely scattered in nature over central
WI and there may even be an isolated storm. Guidance generally
shows these showers fizzling as they move into eastern WI. Brief
reductions of visibilities to MVFR will be possible in the heavier
downpours.

Another round of showers and isolated storms is expected after
midnight through Wednesday morning along a strong cold front. This
round will likely be more widespread (60-80% chance). 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 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.

Steady but light southwest winds will persist this 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.......MPC