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FXUS63 KGRB 280621
AFDGRB

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

Forecast discussion for routine morning forecast issuance

.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.

- 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 06Z TAF Issuance
Issued at 1102 PM CDT Sun Sep 27 2026

SCT to BKN low to mid clouds prevailed across much of the region
late this evening with some patchy fog reported in north-central
WI. These SCT to BKN clouds will stick around through the night as
the patchy fog becomes more widespread in north-central and parts
of central WI, with locally dense fog and IFR/LIFR vsbys between
08-15z Mon. Confidence remains highest for the dense fog at RHI
where some clearing has occurred, and lower at AUW and CWA.
Patchy fog may be possible in some spots in east-central WI, but
confidence is not high enough to include in the east-central WI
TAF sites due to the cloud cover. Any fog will burn off around
14-15z Mon, with SCT mid-level clouds sticking around for much of
Monday. Winds will be light and variable throughout this TAF
period.

&&

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

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kruk