632
FXUS63 KGRB 230618
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
118 AM CDT Thu Jul 23 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Quiet and comfortable weather continues through Friday morning.

- Increasing southerly winds on Friday afternoon and evening may
  lead to hazardous boating conditions for small craft and an
  increased risk for rip currents on Lake Michigan.

- Warmer temperatures and higher humidity return over the weekend
  into early next week, with high temperatures climbing into the
  upper 80s to lower 90s and heat indices reaching into the middle 90s.

- Multiple rounds of thunderstorms will be possible Saturday
  through Monday. The highest potential for organized
  thunderstorms is expected on Sunday afternoon and evening.

&&

.DISCUSSION...
Issued at 108 AM CDT Thu Jul 23 2026

The latest RAP analysis and satellite/radar imagery show a
sprawling surface high pressure system centered from northern
Illinois to Minneapolis early this morning. Clear skies, light to
calm winds, and quiet conditions prevail across north- central and
northeast Wisconsin, with early morning surface temperatures
ranging from the middle 40s across the northwoods to the upper 50s
near the Fox Valley and Lakeshore. This surface high is
maintaining tranquil weather across much of the Upper Midwest,
extending northwestward into the western Plains and central
Canada.

As the high pressure center slides southeast today, thermal
troughing will shift east of the region, allowing low- level
temperatures to moderate back to near-normal mid-summer values.
Diurnal heating will prompt fair-weather cumulus to build around
15Z to 17Z with initial bases around 4000 to 5000 feet, rising to
6000 to 8000 feet in the afternoon before clearing early this
evening. Afternoon high temperatures today will reach the upper
70s to lower 80s. Light westerly winds this morning will turn
southwest to south at 5 to 10 knots during the afternoon, with a
few localized gusts up to 15 knots. Looking upstream over the next
36 to 48 hours, an upper-level ridge building northeastward from
the Plains into the northern Mississippi Valley will maintain warm
advection while keeping the primary convective storm track well
displaced to the northwest over the northern Plains through
Friday.

Thunderstorm potential increases over the weekend as an active
northwest flow regime establishes itself on the eastern periphery
of the building upper ridge. On Saturday, a weak mid-level
shortwave impulse and an accompanying decaying cold front will
track across the region. Instability will build to 1000 to 2000
J/kg over north-central Wisconsin by Saturday afternoon, which
when combined with 30 to 35 knots of deep-layer shear will create
an environment favorable for strong storm development.
Precipitation focus appears highest over far northern Wisconsin
near stronger low-level convergence, though activity is expected
to show a diminishing trend as it pushes east. Sunday presents the
highest potential for organized severe weather across the region
as a warm front lifts toward central Wisconsin beneath strong warm
advection aloft. An airmass characterized by 1500 to 2500 J/kg of
CAPE and 40 knots of deep-layer shear beneath a 90th percentile
500mb jet streak will provide a favorable parameter space for
severe storms. Mid-level capping may serve as a hindrance to
convective initiation, but any storms capable of breaching the cap
will have potential to become severe. Storm chances linger into
Monday as a stronger upper shortwave trough and surface cold front
traverse the Great Lakes.

Along with returning storm chances, a hot and humid airmass will
build into the state for the late weekend. High temperatures in
the low to mid 80s on Friday and Saturday will climb into the
upper 80s to lower 90s on Sunday and Monday. Surface dewpoints
rising into the upper 60s and lower 70s will produce afternoon
heat indices in the middle 90s across central and east-central
Wisconsin. While convective debris and thunderstorm coverage may
offer localized temperature relief at times, the heat and humidity
will create uncomfortable conditions. A cold front passing Monday
night will usher in cooler and drier air for Tuesday and
Wednesday, bringing high temperatures back to near normal in the
upper 70s and lower 80s.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1042 PM CDT Wed Jul 22 2026

KOSH...Clear skies and light and variable winds will prevail
overnight into Thursday morning. Fair weather cumulus clouds
between five and six thousand feet will develop between 16-17z
and continue through the afternoon. A prevailing southwest wind
of 5 to 10 knots is expected throughout most of the day. Winds
should back to the south late in the day into the evening with
clearing skies.

Rest of north-central and northeast WI, clear skies and light
and variable winds will continue into Thursday morning. Fair
weather cumulus clouds between four and six thousand feet is
expected to develop between 15-17z and continue throughout the
afternoon. Southwest winds of 5 to 10 knots are forecasted with
winds backing to the south during the late afternoon and
evening. The only exception will be along the Lake Michigan
shoreline where winds should back south/southeast by or around
18z. Skies will clear during the evening.

&&

.MARINE...
Issued at 108 AM CDT Thu Jul 23 2026

As high pressure shifts toward the East Coast on Friday, the
surface pressure gradient will tighten across the western Great
Lakes, helping to produce breezier southerly winds over Lake
Michigan to 15 to 25 knots Friday afternoon. Building wave heights
to 3 to 5 feet will may require a Small Craft Advisory for the
Lake Michigan nearshore waters and a Beach Hazard Statement for
the Lake Michigan shoreline.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

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

NWS GRB Office Area Forecast Discussion