129
FXUS63 KGRB 030353
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1053 PM CDT Wed Sep 2 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Multiple rounds of thunderstorms are possible late tonight
  through Thursday. A few strong to severe thunderstorms are
  possible with damaging winds and large hail being the main
  threats.

- Above normal temperatures and periodic rain/storm chances will
  continue through the weekend.

&&

.DISCUSSION...
Issued at 213 PM CDT Wed Sep 2 2026

Dry conditions will prevail for the remainder of the day as a weak
ridge builds over the region. Tonight areas of patchy fog will again
be possible with light winds and a moist boundary layer. A round of
showers/thunderstorms is expected to develop overnight/early
Thursday morning across IA and southwest WI along the noise of a
strengthening LLJ. There is still a lot of spread amounts the latest
CAMs as to how morning convection will play out exactly, but a
parameter space of ~1500 J/kg and 40-45kt 0-6km shear along and just
north of I-90 does point to at least a low (10-20% chance) for
strong to severe storms with up to 1 inch hail and 40-60 mph wind
gusts as these storms move northeastward through central and east-
central WI. A second round of thunderstorms is possible Thursday
afternoon/evening as a compact mid-level shortwave moves across the
region. CAMs suggest initially discrete cells develop over ND/MN with
the potential to grow upscale into an eastward propagating MCS
during the afternoon. If an organized MCS is able to develop would
expect it to track along the instability gradient from east central
WI toward northern IL. This would put parts of the forecast area,
south of a Merrill to Green Bay line in play, however, there is still
a lot of uncertainty with how convection will evolve through the
afternoon and evening.

The warm and humid airmass will continue to linger over the area
Friday through this weekend keeping on and off chances for showers
and storms each day. However, confidence in the timing of any
precipitation is low as forcing remains rather nebulous due to the
lack of stronger synoptic features.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1053 PM CDT Wed Sep 2 2026

A rather complex TAF period with uncertainty regarding fog, low
clouds and shower/storm chances overnight into Thursday. The
simple part is late this evening where VFR conditions will
prevail as mainly mid/high clouds drift across the region. The
light winds, clear skies will allow for some fog to form, but
guidance not very bullish on anything widespread or dense, with
the higher chances (under 30% for under 3 mile vsby) over eastern
WI. Have included mainly MVFR BR for now and will monitor fog
trends. Low clouds are also possible early Thursday morning, with
some guidance showing a 700-2000 ft deck, but again, not much
agreement to have much confidence this will occur.

Finally, the shower/storm threat is quite muddled, but latest
guidance is increasing the coverage of with elevated convection
possible as early as 07-09z across central and east-central WI,
with a larger area possible after 12-13z Thursday. Depending on
what occurs with those area, another round of showers and storms
may or may not occur Thursday afternoon and evening. The end
result will be plenty of TEMPO and PROB30 groups to account for
the more likely periods of storms, but adjustments will be needed
as the picture will hopefully become a little clearer. There
remains a low-end ~20% chance that a storm becomes strong to
severe with strong wind gusts and hail being the main impacts
along with heavy downpours. Wind will remain fairly light away
from any storm.

&&

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

&&

$$

DISCUSSION.....GK
AVIATION.......Bersch

NWS GRB Office Area Forecast Discussion