550
FXUS63 KGRB 301130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Wed Sep 30 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Rain is expected to continue at times through Thursday. Total
  rainfall amounts between 0.5 and 1" are forecast for portions of
  central to east-central Wisconsin.

- Strong southerly winds will result in hazardous swimming and
  boating conditions on Lake Michigan through this evening.

- Patchy frost will be possible at times across northern Wisconsin
  later this week as a cooler and drier airmass settles in.

&&

.DISCUSSION...
Issued at 100 AM CDT Wed Sep 30 2026

Rain chances through Thursday... Radar currently shows a
northeast/southwest oriented band of scattered showers working
over portions of central and eastern Wisconsin on the nose of 850
mb jet max and broad area of isentropic ascent. This first round
of rain has struggled to make much of itself into the overnight
hours, with QPF totals thus far coming in slightly under forecast.
As it looks right now, subsidence behind this line of showers
looks to afford us a brief break from stratiform rain today, with
activity looking more scattered in nature. Rain chances then
return to eastern Wisconsin late tonight into Thursday morning as
moist conveyor belt from the remnants of Hurricane Polo sneaks
into east-central Wisconsin, increasing PWATs to near 2" (99th
percentile relative to climo) as surface front moves through.
However, with southerly trend coming to fruition, probabilities
for receiving one inch of QPF now only stand at 20 to 40% for
areas south of Hwy 10. A rumble or two of thunder would not be out
of the question this afternoon or evening due to elevated
instability (200 to 300 J/kg) along the front, though no organized
convection is expected.

CAMs once again showing signal for patchy fog development behind
the line of showers this morning as boundary layer remains
saturated. Could certainly see some ground fog developing, though
remain skeptical about dense fog potential due to breezy winds.
Better fog setup looks to be late tonight into early Thursday
morning.

Extended... High pressure builds back in across the Midwest
Thursday evening, lasting through at least the middle of next week.
Only exception will be a 20 to 40% chance for rain on Saturday.
Otherwise, main forecast concerns for the extended center around
frost/freeze potential toward the end of the week as high sits
overhead and 850 mb temperatures fall to near 0C. There will be a
higher likelihood of patchy frost occurrence several times across
the north through early next week, though we could be looking at a
more widespread frost/freeze event Sunday into Monday. Will
continue to monitor trends for headline potential as we approach
the end of the growing season.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 600 AM CDT Wed Sep 30 2026

Cigs have continued to lower to IFR early this morning behind a
SCT line of showers departing to the east. Several sites are
reporting BR or DZ with locally reduced vsbys, likely with some
help from patchy ground fog development as the low levels remain
saturated. Cigs should gradually improve to MVFR, and even VFR, up
near RHI by this afternoon, before once again deteriorating to
low-end MVFR or IFR late tonight. The east-central sites will
likely remain IFR throughout the TAF period.

After a brief break in the stratiform rain this afternoon
and evening, light rain chances return to GRB, ATW, and MTW late
tonight. Have included PROB30 mention of -SHRA from 06 to 12Z
Thursday. A signal then once again exists for patchy fog
development toward the end of the TAF period.

Southwest winds will be sustained at 5 to 10 knots through this
afternoon, gusting between 15 and 20 knots. Winds then subside and
shift to northwesterly late tonight.

&&

.MARINE...
Issued at 100 AM CDT Wed Sep 30 2026

Strong southerly winds will result in a period of hazardous marine
conditions along Lake Michigan nearshore waters through late
tonight. Winds will be sustained at around 10 to 20 knots with
gusts to 25 knots, highest near Death`s Door. Waves will build
between 4 and 6 ft. Waves then subside on Thursday as winds
decrease and veer to the northwest. High waves and strong currents
will also result in dangerous swimming conditions along Lake
Michigan beaches in Manitowoc, Kewaunee, and Door counties.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through late tonight for WIZ022-040-050.
&&

$$

DISCUSSION.....Goodin
AVIATION.......Goodin
MARINE.........Goodin

NWS GRB Office Area Forecast Discussion