563
FXUS63 KGRB 231748
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1248 PM CDT Sat Aug 23 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- First glimpse of early fall expected this weekend into early
  next week with cooler temperatures.

- Some waterspouts are possible Sunday into Monday across the bay
  of Green Bay and the Lake Michigan waters.

&&

.DISCUSSION...
Issued at 256 AM CDT Sat Aug 23 2025

A cold front located over northwest Wisconsin will track through
northern Wisconsin early this morning, bringing a colder airmass
to the western Great Lakes region. Despite a fairly decent line of
showers and thunderstorms associated with the cold front, CAMs
models dissipate the activity as it dives southeast as the storms
move into a more unfavorable environment marked by higher CIN
values. North-central Wisconsin has the highest potential for
seeing showers and thunderstorms before the line dies out.

Behind the cold front the region will remain in cyclonic flow with
an upper level trough slowly moving through southern Canada.
Several shortwaves embedded in the flow will bring opportunities
for showers at times through Monday with the best overall chances
across northern Wisconsin closer to the upper level low with a
boost in moisture from the Great Lakes and the best opportunity
for the entire region to receive rain Sunday afternoon when a
shortwave dives south and tracks through northern Wisconsin.
Temperatures during this stretch will be a solid 10 degrees below
normal with highs Sunday and Monday only ranging from around 60
across the north to the upper 60s across east-central and
northeast Wisconsin.

The cold air moving in across the region will create steep low
level lapse rates and some modest instability inland. This could
bring some thunderstorms with the showers at times on Sunday. The
cool air over the warm waters of Lake Michigan will bring the
potential for waterspouts from Sunday through Monday across the
bay and lake as delta T values soar into the middle 20s with the
convective cloud depth increasing to around 20k ft.

The upper level trough will then push off to the east, allowing a
surface high to build in across the upper Mississippi Valley and
eventually slide southeast towards the Ohio Valley. This will
bring a period of dry weather from Tuesday through the end of the
work week. There continues to be signs that a back door cold front
could sag south through the area Wednesday night into Thursday,
which could bring some showers to the region. Temperatures will
slowly moderate back into the 70s by the middle part of the week,
but still be a solid 5 degrees below normal for this time of year.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1243 PM CDT Sat Aug 23 2025

Widespread stratocumulus clouds have developed across the region,
with most sites reporting VFR ceilings. This will continue
through evening, along with a few light showers in far NC WI.

Partial clearing occurs this evening, but low clouds (MVFR)
are expected to return to northern and parts of central WI late
tonight. Expect the rest of the forecast area to become cloudy
Sunday morning, with scattered light showers possible in most
areas, but especially over NC WI and Door County.

Gusty NW winds will subside early this evening, then increase
again Sunday morning.

&&

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

&&

$$

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