373
FXUS63 KGRB 231103
AFDGRB

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

Updated aviation portion for 12Z TAF 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 12Z TAF Issuance
Issued at 602 AM CDT Thu Jul 23 2026

High pressure shifting southeast across the Great Lakes will
maintain mostly quiet aviation weather and prevailing VFR
conditions today. Mainly clear skies early this morning will give
way to scattered fair weather cumulus around 5-6 kft after 15z,
with bases lifting to 6 to 8 kft this afternoon before
dissipating this evening. Light west winds will continue around 5
to 10 kts this morning before backing to the southwest.

Outlook...VFR conditions persist Friday before thunderstorm
chances increase over the weekend as a warmer, more humid airmass
returns.

.KOSH...
Good flying weather is forecast today with clear skies early in
the morning giving way to scattered fair weather clouds popping
16-17Z. Cloud bases will likely start out 5-6 kft before rising
to 6-8 kft in the afternoon. Clouds will dissipate early this
evening leaving mostly clear skies for the rest of the TAF period.

Light west winds 5 kts or less will back to the southwest (5-10
kts) this afternoon.

&&

.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.......MPC
MARINE.........MPC

NWS GRB Office Area Forecast Discussion