658
FXUS63 KGRB 081903 CCA
AFDGRB

Area Forecast Discussion...CORRECTED
National Weather Service Green Bay WI
203 PM CDT Tue Sep 8 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- One round of showers will exit eastern WI this afternoon.
  Widely scattered showers and thunderstorms are possible again
  late tonight. The risk of severe weather is low.

- Gusty west winds of 25 to 30 mph, with localized gusts up to 35
  mph over north-central Wisconsin, will develop on Wednesday.

- High waves and dangerous rip currents will maintain hazardous
  conditions along Lake Michigan beaches into early Wednesday
  morning.

- Periods of showers and thunderstorms return late Friday through
  Monday.

&&

.DISCUSSION...
Issued at 201 PM CDT Tue Sep 8 2026

The latest RAP analysis and satellite/radar imagery show a
a cold front extending south across Minnesota early this
afternoon. Ahead of this system, strong southwest flow aloft is
drawing moisture into the western Great Lakes region, where
overcast skies and scattered light showers are occurring over
eastern WI. Most of these showers should exit over the next 1-2
hours. While plenty of cloud cover exists over western WI and
Minnesota ahead of the front, portions of the airmass are quite
unstable. Thunderstorms are expected to develop within this
buoyant airmass later this afternoon.

Thunderstorm Potential Tonight...
The primary focus for the short term centers on the aforementioned
cold front, which will sweep across the region tonight. While
instability will gradually increase from the west through the
afternoon, the atmosphere will mainly be capped to surface based
convection despite temperatures rebounding as the rain ends. As a
result, most guidance is dry after the main area of rain exits
northeast WI by 2-3 PM.

Thunderstorm activity will likely develop along the front in a
very buoyant airmass across Minnesota and northern Iowa. This
activity is projected to remain west and south of northeast WI
this evening.

With the approaching front, widely scattered redevelopment of
showers and storms is possible overnight from central to far
northeast WI. Confidence in this redevelopment is relatively low
due to persistent capping and dry air aloft. Patchy ground fog
could develop from central to north-central WI as skies clear and
winds diminish late tonight into early Wednesday morning.

Gusty Winds Wednesday...
Behind the cold front on Wednesday, clearing skies in the morning
will promote strong daytime surface heating and efficient
boundary- layer mixing. Steep low-level lapse rates will support
gusty west winds of 25 to 30 mph across the area, with localized
gusts reaching up to 35 knots across north-central Wisconsin where
deeper mixing is anticipated. Highs on Wednesday will warm into
the mid 70s to low 80s. Winds will diminish Wednesday night as
high pressure slides into the region, bringing clear skies and
cooler overnight lows in the mid 40s to mid 50s.

Thunderstorm Potential Friday through Monday...
Moving into the late-week period, the upper-level flow pattern from
Thursday through Monday will feature general troughing spanning from
the Pacific Northwest to eastern Canada, juxtaposed against a
suppressed subtropical ridge over the southern tier of the country.
A shortwave lifting northeast across the northern Plains into south-
central Canada will propel a cold front through the forecast area
late Friday night into Saturday morning. While synoptic dynamics are
respectable, a narrow moisture axis with precipitable water values
around 140 percent of normal will precede the boundary. Thunderstorm
potential will be constrained by a significant cap centered near 800
mb, with elevated CAPE of 600 to 800 J/kg located above the
inversion. Instability is expected to diminish rapidly with eastward
extent into Saturday morning, keeping the severe weather threat low.

For the remainder of the extended period Sunday into Monday, the
cold front is forecast to stall and return northward as a warm
front as a wave of surface low pressure tracks northeast along the
boundary across the region. Considerable model spread remains
regarding the exact track and timing of the surface low, resulting
in low confidence in specific timing details. However, robust
synoptic forcing and modest MU CAPE generate a notable heavy rain
signal in the Extreme Forecast Index (EFI) across northern and
northwest Wisconsin. Elevated convection capable of producing
heavy rainfall will need to be monitored over the coming days.
High temperatures will generally average in the upper 60s to mid
70s through the weekend and early next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1200 PM CDT Tue Sep 8 2026

An area of showers will be exiting northeast WI early in the TAF
period. Widespread MVFR and IFR ceilings exist over northwest
Wisconsin and northwest Minnesota behind the showers, which will
impact RHI/AUW/CWA this afternoon. Confidence is higher at AUW/CWA
than at RHI that a period of VFR ceilings will return late this
afternoon and into the evening. Will monitor the Fox Valley for
lower ceilings, but will keep flight conditions VFR for now.

Scattered showers and isolated storms (30-40% chance) could
redevelop late this evening into the overnight along a cold front.
Have adjusted the timing of the prob30 groups from the previous
forecast.

Ceilings are forecast to fall to low MVFR and IFR with the above
mentioned cold frontal passage at all terminals late tonight.
Patchy fog may develop as skies clear behind the front. This could
impact RHI/AUW/CWA for a few hour period between 09-13Z Wed.

Clearing skies and improving flight conditions to VFR are forecast
after 13-15Z Wed. Gusty west winds to 20-25 kts are then forecast
to develop by the end of the TAF period.

&&

.MARINE...
Issued at 201 PM CDT Tue Sep 8 2026

Southerly winds will increase this afternoon and result in high
waves on the nearshore waters of Lake Michigan and
southern/central Green Bay. Conditions will be hazardous to small
craft until early Wednesday morning. There will also be an
increased risk of rip currents on Lake Michigan beaches, until
winds turn offshore. Small Craft Advisories and Beach Hazards
Statements are in effect through 7 AM Wednesday.

Another Small Craft Advisory may be needed for Wednesday
afternoon/evening for increasing west winds, but forecast wind
gusts have diminished somewhat. Confidence is sufficiently low to
hold off on marine headlines.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through Wednesday morning for WIZ022-040-
050.
&&

$$

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

NWS GRB Office Area Forecast Discussion