400
FXUS63 KGRB 010017
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
717 PM CDT Fri Jul 31 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Widespread rain with a few thunderstorms will overspread north-
  central and northeast Wisconsin through Saturday morning. No
  severe weather is expected.

- There is an increased risk for rip currents along Lake Michigan
  beaches south of Sturgeon Bay on Saturday night and Sunday.

- Quiet weather returns Saturday night through Monday.

- Scattered showers and thunderstorms return Tuesday and Wednesday
  as a cold front moves through the region.

&&

.DISCUSSION...
Issued at 106 PM CDT Fri Jul 31 2026

A 1006 mb surface low centered over northern Iowa early this
afternoon will track slowly southeast toward central Illinois
tonight, before continuing eastward into the Ohio Valley on
Saturday. An arcing band of warm advection rainfall is currently
spreading northeast across southwest Wisconsin. Lightning is
relatively sparse over the northern Mississippi Valley so far
today, and radar returns have been weakening as they move closer
to central Wisconsin. Another area of light rain is occurring over
far northern WI and the Upper Peninsula along a 700mb gradient.
As this low moves across the region, rain and thunderstorm trends
remain the focus of this forecast.

Rainfall will continue to lift northeast and intensify through
early this evening as low-level warm advection strengthens
downstream of the Iowa low. While the overall boundary layer
remains relatively stabilized by widespread cloud cover and
earlier rain, isolated storms cannot be ruled out and most likely
near the U.P. border. The rain will likely continue over northeast
Wisconsin through Saturday morning before ending. With daytime
heating, a few widely scattered showers could also develop in the
afternoon from central to far northeast WI.  The highest
probabilities for 1 inch or greater of rainfall (30-50%) remain
situated south of a Marshfield to Green Bay line, with the highest
confidence in localized 1-inch amounts extending from Wautoma
toward Manitowoc. Highs on Saturday will be held in the 70s under
cloud cover and persistent northeast winds.

Surface high pressure will build into the Upper Great Lakes
Saturday night and remain dominant through Monday night. This will
yield clear to partly cloudy skies, light winds, and pleasant
mid-summer conditions. High temperatures will steadily warm from
the mid and upper 70s on Sunday to the lower and mid 80s on Monday
under ample sunshine.

The next notable weather system arrives Tuesday into Wednesday as
an upper-level shortwave trough and associated surface cold front
push east across the Northern Plains into the Upper Midwest.
Moisture return ahead of the boundary will push dew points back
into the 60s, generating MUCAPE of 500-1000 J/kg and deep-layer
shear of 25-30 knots. This environment will bring scattered
showers and thunderstorms from Tuesday afternoon through Wednesday
morning. While severe weather risk remains low at this time due to
modest instability, parallel flow aloft relative to the frontal
boundary could result in localized training of shower activity.
Lighter precipitation chances linger into Thursday as cooler,
near-normal air settles back over the region with highs returning
to the upper 70s and lower 80s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 717 PM CDT Fri Jul 31 2026

Periods of light to moderate rain are expected to continue across
the region through tonight, becoming mainly focused across east-
central WI by Saturday morning. VFR conditions are mainly
expected through this TAF period, but cigs will drop to MVFR
across the east-central WI TAF sites when the rain becomes more
steady late tonight through Saturday morning. The rain will come
to an end to the southeast Saturday afternoon.

There are also indications of fog development in far north-
central WI late tonight, which may cause reduced IFR vsbys at the
RHI TAF site for a period early Saturday morning.

Light and variable winds will become north/northeasterly overnight
into Saturday. Gusts of 15 to 20 kts are possible at the east-
central WI TAF sites late tonight through Saturday, with a few
gusts to 15 kts at the central and north-central WI TAF sites
Saturday afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 4 AM CDT Saturday through Sunday
evening for WIZ050.
&&

$$

DISCUSSION.....MPC
AVIATION.......Kruk

NWS GRB Office Area Forecast Discussion