011
FXUS63 KGRB 281054
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
554 AM CDT Mon Sep 28 2026

Updated aviation portion for 12Z TAF issuance

.UPDATE...
Issued at 455 AM CDT Mon Sep 28 2026

Surface observations have steadied out to more of a bank of dense
fog with one quarter of a mile visibility instead of bouncing
between lower and higher visibilities early this morning. In
addition, area webcams show the dense fog has become more
persistent and widespread than early this morning. Therefore, will
issue a Dense Fog Advisory for north-central Wisconsin through 10
am, when the dense fog is expected to dissipate. Right now it
appears the dense fog is staying north of central Wisconsin, but
will monitor for further expansion if necessary.

&&

.KEY MESSAGES...

- Patchy dense ground fog is expected this morning across central
  and north-central Wisconsin, locally reducing visibilities below
  1 mile before clearing by 10 AM. A Dense Fog Advisory is in
  effect for north-central Wisconsin.

- Patchy dense ground fog is possible late tonight into Tuesday
  morning across eastern Wisconsin.

- Rain shower and thunderstorm probabilities increase to 60 to 90
  percent Tuesday night into Wednesday night as a slow-moving
  upper-level trough and surface cold front traverse Wisconsin.

- Cooler conditions filter in behind the cold front Thursday
  through the weekend, with high temperatures falling into the
  low-60s and overnight lows dropping into the mid-30s across
  north-central Wisconsin.

&&

.DISCUSSION...
Issued at 120 AM CDT Mon Sep 28 2026

Patchy Dense Fog this Morning and again Tonight: Cloud cover is
ubiquitous across the region early this morning, which has limited
the scope and severity of the fog across north-central Wisconsin.
However, cloud cover is still expected to thin out through 5 AM.
The decreased cloud cover, combined with radiational cooling and
light winds still favors nocturnal ground fog development later
this morning across mainly north-central Wisconsin. NBM
statistics for visibilities below 1 mile have decreased to 20 to
40%, mainly across north-central Wisconsin with central Wisconsin
down to around 10%. Any fog that forms will rapidly dissipate by
10 AM as morning solar heating drives boundary layer mixing.

The threat for fog shifts to the east tonight into Tuesday morning
as the hi res models and HREF indicate some patchy fog is possible
across east-central and far northeast Wisconsin. There is more
spread in visibilities, with lower chances for visibilities less
than 1 mile; however, this will still bear watching as the fog
forecasting has been tricky the last few days.

Prolonged Dry And Mild Early Week Pattern: Deep-layer atmospheric
subsidence associated with the persistent surface high pressure
ridge will lock in dry and tranquil weather across the forecast
area through Tuesday afternoon. Inland high temperatures will
warm into the mid-70s today, while light onshore lake breezes
keep Lake Michigan shoreline communities slightly cooler in the
upper 60s. NBM ensemble guidance exhibits high confidence with
tight 10th to 90th percentile temperature spreads of only 2 to 3
degrees F for daily highs today.

Midweek Frontal System And Widespread Rainfall: Deterministic and
ensemble guidance consensus tracks a slow-moving northern stream
trough and advancing surface cold front into the Upper
Mississippi Valley Tuesday night into Wednesday night. Strong
low-level moisture transport will elevate rain probabilities to
60 to 90 percent Tuesday night through Wednesday night. NBM
probabilistic guidance indicates a 70 to 90 percent probability
of 48-hour QPF exceeding 0.50 inches across the region, with a
solid 60 to 80 percent of 1 inch or more, and 30 to 60 percent
chance of 2 inches or more west of the Fox Valley. NBM 50th
percentile liquid accumulation ranges between 1.50 and 2.6
inches along and west of the Fox Valley. SBCAPE values under 300
J/kg and poor shear-moisture overlap will keep thunderstorm
activity isolated, mainly south of highway 10, and mitigate any
severe weather potential.

Late Week Cooling Trend And Frost Potential: Post-frontal cold
air advection will usher in a cooler and drier airmass Thursday
through the weekend, dropping daytime highs into the low to
mid-60s area-wide. As high pressure builds southward from Canada,
light winds and clearing skies will promote efficient radiational
cooling on Friday night. NBM temperature percentiles show
overnight minimum temperatures dropping into the mid to upper 30s
across Vilas, Oneida, and Forest counties Friday night. This setup
yields a 15 to 30 percent probability of frost in sheltered low-
lying spots across the Northwoods before high pressure begins
shifting east over the weekend.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 554 AM CDT Mon Sep 28 2026

Widespread LIFR/VLIFR fog has formed across north-central
Wisconsin, mainly impacting RHI. At this time the fog looks to
stay north of the rest of the TAF sites given drier air or clouds
impeding radiational cooling. Any fog should mix out by 14-15Z.

SCT mid-level clouds will then prevail much of today. Additional
fog is expected to develop late tonight, mainly across northeast
and east-central Wisconsin. This could impact the ATW/GRB/MTW TAF
sites. The fog could reduce conditions to MVFR, with IFR
conditions possible. Confidence in dense fog tonight is lower than
this morning; therefore, will not lower conditions beyond MVFR
until the scope of the fog becomes clear. Winds will be light and
variable throughout this TAF period.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CDT this morning for WIZ005-
010>012-018-019.
&&

$$

UPDATE.........Kurimski
DISCUSSION.....Kurimski
AVIATION.......Kurimski

NWS GRB Office Area Forecast Discussion