995
FXUS63 KGRB 300630
AFDGRB

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

Forecast discussion for routine morning forecast 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 06Z TAF Issuance
Issued at 951 PM CDT Tue Sep 29 2026

Overview: A slow-moving cold front will bring widespread rain and
deteriorating flight conditions tonight through Wednesday
morning. Then a slow, gradual improving trend Wednesday
afternoon while MVFR/IFR ceilings continue over central to east-
central WI through Wednesday evening.

Through 12Z, the cold front will bring bring widespread
-SHRA/BR with lowering ceilings to IFR and vsbys 3-5SM. Low-
level wind shear hazard (LLWS 2000 ft 220-230/35-40 kt) at KAUW,
KCWA, KATW, KMTW, and KGRB between 02Z-08Z.

12Z-20Z Wed: Widespread light rain changes to a drizzle and mist.
Widespread LIFR/IFR ceilings (400-900 ft AGL) with drizzle/mist
(-DZ BR) very slowly lifting to IFR/MVFR toward 16Z-20Z at KRHI,
KAUW, KCWA. The greatest improvements will likely occur at KRHI.
SW-W winds 6-10 kts.

20Z Wed-01Z Thu: Further ceiling improvements are expected at
KRHI, KAUW, KCWA but only very small improvements are possible
over the Fox Valley and Lakeshore.

01Z-06Z Thu: Guidance is showing ceilings deteriorating again over
central and east-central WI and back to low end MVFR or IFR. Some
potential for fog to develop by late in the taf period over areas
where clearing occurs.

Confidence/Outlook: High confidence in LIFR/IFR ceilings 06-18Z
Wed.

&&

.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 from 4 AM CDT early this morning through
late tonight for WIZ022-040-050.
&&

$$

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

NWS GRB Office Area Forecast Discussion