936
FXUS63 KGRB 011824
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
124 PM CDT Sat Aug 1 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Widely scattered showers and isolated thunderstorms this
  afternoon and early evening.

- There is an increased risk for rip currents along Lake Michigan
  beaches in Kewaunee and Manitowoc from late tonight though
  Sunday afternoon.

- Relatively quiet weather returns tonight through Monday night.

- Scattered showers and thunderstorms return Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 123 PM CDT Sat Aug 1 2026

Latest RAP analysis and satellite/radar imagery early this
afternoon show a closed low pressure system spinning across
central Illinois and southern Indiana. Light rain on the northern
periphery of this feature has nearly exited east-central
Wisconsin, leaving behind extensive cloud cover over southern
counties. Farther north across north-central to far northeast
Wisconsin, visible satellite depicts an expanding field of fair
weather cumulus developing within an axis of 500 to 1000 J/kg
of surface based instability. Over the next 36 to 48 hours, the
central Illinois surface low will track slowly east- southeastward
toward the Ohio Valley, allowing high pressure over Ontario and
the Upper Lakes to build southward into the western Great Lakes
region.

As convective temperatures are approached this afternoon (around
2 PM to 3 PM), widely scattered showers and isolated thunderstorms
are expected to initiate across north-central and northeast
Wisconsin. Low-level surface convergence is relatively weak, but
mesoanalysis indicates sufficient destabilization to support
pulse-type convective updrafts. CAMS guidance indicates the
highest probability for shower and storm activity will extend
along a corridor from Marinette County southwest through Wood and
Waushara Counties, with some CAMS tracking scattered activity into
the Fox Valley between 6 PM and 8 PM. Model forecast soundings
exhibit shallow inverted-V profiles in the lowest levels, which
will support localized wind gusts of 25 to 30 mph and brief
visibility reductions under stronger showers. Convection should
quickly wane mid to late evening with the loss of diurnal heating
and the departure of the surface low to the southeast.

Attention then turns to cloud cover and temperature trends
overnight into Sunday, as well as marine impacts. As the surface
low pulls further away into the Ohio Valley, a tightening pressure
gradient and a longer fetch of northeast winds across Lake
Michigan will push a surge of low stratus into northeastern and
central Wisconsin late tonight into early Sunday morning. These
low ceilings are expected to gradually lift into a
stratocumulus/cumulus field by late Sunday morning as diurnal
heating and dry air advection take hold. Skies should clear from
north to south Sunday afternoon as strong surface high pressure
builds south out of Ontario. High temperatures on Sunday will be
somewhat suppressed by the low clouds and onshore flow, ranging
from the mid 70s near Lake Michigan to near 80 degrees across
central Wisconsin.

High pressure will center over the western Great Lakes Sunday
night through Monday night, bringing a period of quiet and
pleasant weather with near-normal temperatures and comfortable
humidity. Highs on Monday will reach the upper 70s to mid 80s
under mostly sunny skies. The next weather maker approaches
Tuesday as a shortwave trough and associated surface cold front
track eastward across the Upper Midwest. Convective parameters
ahead of the boundary appear modest, with MUCAPE values peaking
around 500 to 1000 J/kg and deep-layer shear around 25 to 30
knots. This combination suggests a minimal threat for organized
severe weather. However, precipitable water values rising to 120
to 130 percent of normal alongside deep-layer flow aligned
parallel to the surface frontal boundary could promote localized
training of showers and storms, presenting a low risk for
localized heavy rainfall.

Most global ensemble guidance rapidly pushes the cold front east
of the area by Wednesday morning, though lingering light rain
showers cannot be ruled out over northeast Wisconsin early
Wednesday. A notable outlier in deterministic guidance (GFS) holds
the front up and delays its eastern progression, maintaining
heavy rainfall potential into Wednesday, but this solution lacks
support from ensemble cluster means. High pressure builds back
into the Upper Mississippi Valley behind the front for Wednesday
and Thursday, returning dry weather and seasonal conditions. The
next upper-level shortwave and cold front will bring the next
opportunity for showers and thunderstorms toward next Friday into
Saturday. Temperatures throughout the 7-day period will remain
right around seasonal averages, with daily highs in the mid 70s to
mid 80s and overnight lows in the upper 40s to low 60s.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1156 AM CDT Sat Aug 1 2026

Steady light rain continues to impact areas from OSH to MTW late
this morning. This rain should be ending near or shortly after TAF
issuance. Ample low level moisture will likely lead to a period of
MVFR ceilings over east-central WI and perhaps central WI until
18-20Z before lifting to VFR. Thereafter, ceilings should remain
VFR through early evening.

Low level convergence and unstable conditions should lead to
widely scattered showers and isolated thunderstorms developing
between 20-01Z. The latest guidance indicates the most probable
location stretches from Marinette County to Wood/Waushara
Counties. This area is generally between AUW/CWA and GRB/ATW, but
will monitor trends as some models bring the shower activity into
GRB/ATW between 23-01Z. Brief MVFR visibilities and gusty winds
25-30 mph will be possible in the stronger shower activity.

The latest indications show that a longer fetch of northeast winds
will bring in a surge of MVFR ceilings late tonight into Sunday
morning. Adjusted timing a bit based on RAP data. These ceilings
have potential to impact all TAF sites, though confidence is not
as high over RHI/AUW/CWA. These MVFR ceilings should lift into a
cumulus field by late Sunday morning.

&&

.MARINE...
Issued at 123 PM CDT Sat Aug 1 2026

The persistent northeast fetch will also create hazardous
conditions for mariners on Lake Michigan, with winds increasing to
15 to 25 knots and waves building to 3 to 5 feet on Sunday. The
current small craft advisory is struggling north of Sheboygan
based on latest surface and marine observations. However, winds
and waves are expected to increase late tonight into Sunday which
should result in hazardous conditions south of Sturgeon Bay.

As for headlines, have adjusted the small craft advisory between
Sturgeon Bay and Two Rivers to start at 6 AM Sunday. The Beach
Hazard Statement and Small Craft Advisory adjacent to the
Manitowoc shoreline will continue despite the lackluster winds and
waves so far today.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through Sunday evening for WIZ050.
&&

$$

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

NWS GRB Office Area Forecast Discussion