799
FXUS63 KGRB 131121
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
621 AM CDT Sun Sep 13 2026

Updated aviation portion for 12Z 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 into
  Tuesday. The severe weather threat is low.

- Hazardous conditions for small craft are likely Monday afternoon
  into Tuesday afternoon due to gusty southerly winds or high
  waves.

- High waves will lead to an increased risk of rip currents at
  Lake Michigan beaches Monday afternoon into Tuesday afternoon.

&&

.DISCUSSION...
Issued at 233 AM CDT Sun Sep 13 2026

Today: Shortwave currently dropping south across northern MN will
move across the region this morning bringing mostly cloudy skies and
possibly a brief sprinkle south of HWY 10. High pressure works back
in this afternoon retuning dry and partly sunny skies to the area.
With high pressure overhead tonight expect clear and calm conditions
which will allow temperatures to fall into the low to middle 30s
across north-central WI. Widespread frost is possible along and
north of HWY 8, if you have cold sensitive plants plan to bring them
indoors or cover them.

Heavy Rain Monday into Tuesday: A strong low pressure system,
currernly coming onshore over the PNW will track into the northern
Plains Monday. Ahead of this system strong isentropic ascent is
expected over WI in association with a LLJ. This will likely lead to
a widespread area of moderate rain pushing into the region Monday
afternoon and continuing into Tuesday. PWATs with this system are
expected to climb to near 2" (around the 99th percentile of
climatology) most areas have at a 70-90% chance for at least 1" of
rain. Pockets of higher amounts of 2-3" are possible, mainly across
central WI, with the NBM showing a 30-50% chance for over 2" west of
I-39. The severe storm threat with this system appears rather low
with a lack in much instability and a strong near surface
temperatures inversion.

Rest of Next Week: A baroclinic zone is expected set up over or near
the forecast area for the middle and end of next week. This will
keep a 30-50% chance for showers and occasional thunderstorms
Wednesday through Friday, however, it will likely not rain that
entire period. Temperatures will hover near to slightly below normal
next week depending on where the boundary sets up each day.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 621 AM CDT Sun Sep 13 2026

VFR conditions expected through the TAF period. Intervals of SCT-BKN
mid and high clouds will occur this morning with skies becoming
increasingly clear by afternoon. VFR cu today as well, mainly across
northern WI. Light northwest winds will increase to 10-20 kts, with
a few gusts up to 25 kts at times. Winds will become calm tonight
with high pressure settling overhead.

&&

.MARINE...
Issued at 233 AM CDT Sun Sep 13 2026

Another period of gusty southerly winds will lead to increasing
waves, along with an increasing risk of rip currents Monday into
Tuesday. A Small Craft Advisory or Gale Warning and Beach Hazard
Statements will likely be needed.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from midnight tonight to 8 AM CDT Monday for
WIZ005-010>012-018.
&&

$$

DISCUSSION.....GK
AVIATION.......GK
MARINE.........GK

NWS GRB Office Area Forecast Discussion