820
FXUS63 KGRB 140408
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1108 PM CDT Sun Sep 13 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- The first widespread frost of the season is expected across the
  north late tonight into early Monday morning. A few of the
  typical colder locations could drop to or slightly below
  freezing for a few hours.

- A round or two of heavy rain and storms is possible Monday in to
  Tuesday. Rainfall amounts over an inch are possible in spots.
  The severe weather threat is low.

- Hazardous conditions for small craft return Monday afternoon and
  continue into Tuesday. Small Craft Advisories or a Gale Watch is
  in effect Monday afternoon and Monday night. Additional marine
  headlines will be needed on Tuesday due to gusty winds or
  diminishing waves.

- High waves will lead to an increased risk of rip currents at
  Lake Michigan beaches Monday afternoon into Tuesday afternoon
  where a Beach Hazardous Statement is in effect.

&&

.DISCUSSION...
Issued at 232 PM CDT Sun Sep 13 2026

The first signs of fall as temperatures as of mid-afternoon were
in the middle to upper 60s under partly cloudy skies. Gusty
northwest of 10 to 20 mph were noted with gusts up to 25 mph.
Dewpoint readings across the north have fallen into the middle
to upper 30s.

For tonight, high pressure will slide eastward and will be
centered across northeast WI overnight. The combination of clear
skies and light winds will allow temperatures to plummet
into the 30s over northern WI and in some sections of central
WI. A few our our typical cold spots may drop to or a few
degrees below freezing for a couple of hours around sunrise.
Expanded the Frost Advisory to include Langlade, and northern
sections of Marinette and Oconto counties with the afternoon
issuance.

Attention turns to the next system that will bring the next
round of rain and a few thunderstorms. Latest model trends
would suggest rain would be a few hours slower arriving across
far northeast WI and probably would not occur until early evening.
The risk of severe weather is very low with models indicating the
most unstable CAPE values of 50-150 J/KG across central into
northeast WI Monday evening. The NBM was highlighting a 60-90%
chance of 1 inch or more of rain from Marshfield to Wausau
to Merrill northeast into Marinette County. The probabilities drop
off sharply to 15 to 30% from Green Bay and Appleton and points
to the southeast and east. The NBM also showed a 50-70% chance
of 2+" of rain from Wausau to Marshfield. The LREF probabilities
were somewhat lower, but were still highlighting the heaviest
rainfall out towards Wausau. Any rain across northeast WI will
come to an end Tuesday morning.

High pressure will build into the region on Tuesday, although
gusty winds will continue to bring some hazardous conditions
on the bay and lake. The previous forementioned baroclinic zone
is expected to set up south of the area for the rest of the week.
A wave moving along the boundary could bring a chance of
rain Wednesday afternoon into Wednesday night, although
confidence is low on the northward extent of the precipitation
field. The models are in an agreement that feature moving across
the area Friday night into Saturday will likely be the highest
chances/greatest confidence in the chances for rain during the
period. Temperatures for much of the period will be at or slightly
above normal.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1106 PM CDT Sun Sep 13 2026

VFR conditions persist through Monday afternoon, before conditions
deteriorate Monday evening into early Tuesday. Skies will be mostly
clear rest of tonight with areas of frost over north-central and
far northeast WI late tonight. Winds will be light and variable.

On Monday, rain will arrive from the west in the afternoon and
evening, with scattered thunderstorms embedded in the large area
of rain. Even with the rain, conditions through 00z Tuesday should
remain VFR. Southeast winds will increase on Monday, with gusts
over 20 kts on Monday afternoon.

Rain with embedded thunder will continue statewide. CIGS are
likely to drop into the MVFR category on Monday evening, with
areas of IFR CIGS developing through the night central to north-
central WI. Local IFR-MVFR visibility will also occur. The rain
should end late Monday night into early Tuesday morning, but
CIGS will only slowly improve on Tuesday.

&&

.MARINE...
Issued at 1107 PM CDT Sun Sep 13 2026

Hazardous conditions return to the lake and bay Monday afternoon
and continue into Tuesday afternoon. The next round of marine
headlines is now set. A Small Craft Advisory is in effect from 4
pm to 9 pm Monday, while a Gale Warning is in effect from 9 pm
Monday to 7 am Tuesday. Due to lingering gusty winds and high
waves on Tuesday, an additional Small Craft Advisory is in effect
for the bay from 7 AM to 4 PM on Tuesday, and on the lake from 7
AM to 7 PM on Tuesday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 8 AM CDT Monday for WIZ005-010>013-018-019-
021.

Beach Hazards Statement from Monday evening through Tuesday
evening for WIZ022.

Beach Hazards Statement from Monday afternoon through Tuesday
afternoon for WIZ040-050.
&&

$$

DISCUSSION.....Eckberg
AVIATION.......JLA
MARINE.........Eckberg

NWS GRB Office Area Forecast Discussion