987
FXUS63 KGRB 041919
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
219 PM CDT Sat Oct 4 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Very warm again temperatures will continue through Sunday with
  highs on Sunday ranging from the upper 70s to middle 80s.
  Several record high minimums are expected tonight.

- Conditions hazardous to small craft from late this afternoon
  through early Monday morning.

- Gusty winds paired with very warm temperatures this weekend will result
  in increased fire weather potential.

- Rain chances return late Sunday afternoon across north-central
  WI, then impact all areas Sunday night through Monday night. The
  probability of receiving more than a quarter inch of rainfall is
  less than 20%.

&&

.DISCUSSION...
Issued at 217 PM CDT Sat Oct 4 2025

Short Term...Tonight and Sunday

The latest RAP analysis and radar/satellite imagery show a cold
front stretching from northwest Minnesota to eastern Nebraska with
broad southerly flow across the western Great Lakes this
afternoon. This pattern is leading to unseasonably warm
conditions, with temperatures pushing into the lower to middle 80s
under mostly clear to partly cloudy skies. Many record high
temperatures are expected to be broken today (a few already have,
preliminarily). In addition, southerly wind gusts are increasing,
with some gusts over 25 mph reported in central and north-central
Wisconsin. As the cold front over the northern Plains tracks
eastward, the primary forecast concerns through the weekend will
revolve around record heat, elevated fire weather conditions, and
marine hazards.

Elevated Fire Weather: Fire weather conditions will be a concern
through Sunday. For today, minimum humidity values are expected to
fall to around 35-40 percent with wind gusts to 30 mph this
afternoon, leading to a minor fire weather potential. The concern
is greater for Sunday, with forecasted wind gusts up to 35 mph and
an additional day for the drying and curing of fine fuels. These
winds would be strong enough to support the spread of any fires
that may start, including those from power lines. According to our
fire weather partners, heavier fuels are not yet fully cured as
leaves are still primarily on the trees, which should temper the
overall threat.

Boating Hazards: Small Craft Advisories will be in effect this
weekend for Lake Michigan and the Bay of Green Bay due to gusty
south winds and high waves. On Lake Michigan, waves are expected
to build to 4 to 6 feet this evening and reach nearly 10 feet on
Sunday afternoon. A Small Craft Advisory will be issued for the
Bay of Green Bay from 10 AM Sunday through 4 AM Monday for gusty
winds of 25 to 30 knots and waves of 3 to 5 feet. The advisory for
Lake Michigan may need to be extended further into Monday morning
due to lingering high waves.

Thunderstorms: As the cold front approaches the area, the chance
for rain will increase over north-central Wisconsin between 4 PM
and 7 PM Sunday. The chance for thunderstorms is very low due to
meager instability, with CAPE values generally under 100 J/kg. As
a result, no severe weather is expected.

Strong Winds: Gusty south winds will be a concern for aviation
interests. Surface wind gusts of 20 to 25 knots are expected this
afternoon, increasing to 30 knots on Sunday. Overnight tonight, as
the surface layer decouples, significant low-level wind shear of
40 to 50 knots is expected to develop and persist through mid-
morning Sunday.

Long Term...Sunday Night Through Saturday

A significant pattern change is on tap for next week as a deep
trough swings through Ontario and Quebec on Tuesday and Wednesday.
This will allow a slow-moving cold front and a Canadian surface
high-pressure system to bring much cooler, more seasonable air
into the Great Lakes region for the middle of the week.

Rainfall Potential: The approaching front will bring the next
chance for widespread precipitation, primarily on Monday over
northeast Wisconsin as deeper moisture moves into the frontal
zone. The airmass lacks deep Gulf moisture and is characterized
by little to no instability. Therefore, the probability of
receiving a quarter- inch of rain is low and under 20%.

Temperatures: Behind the front, temperatures will fall back to
seasonable levels for the middle of the week, with high
temperatures in the 50s and 60s. Overnight low temperatures are
expected to drop into the lower to middle 30s over far northern
Wisconsin on Tuesday night making frost a distinct possibility.

Elevated Fire Weather: There is a conditional concern for fire
weather later in the week. If north-central Wisconsin receives
little rainfall with the frontal passage and a subsequent hard
freeze occurs, the fire weather potential could increase again as
fuels continue to dry out and cure. Temperatures are forecast to
rebound to above-normal levels by next Friday and Saturday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1155 AM CDT Sat Oct 4 2025

High confidence in VFR conditions prevailing at all terminals
(KGRB, KATW, KMTW, KAUW, KCWA, KRHI) through the forecast period
under mostly clear skies. The primary aviation concerns will be
gusty surface winds and significant low-level wind shear (LLWS).

A tightening pressure gradient will result in gusty southerly
surface winds of 20 to 25 kts this afternoon. As the boundary
layer decouples this evening, surface winds will decrease, but a
strong low-level jet will develop. This will create LLWS of 40-50
kts overnight, persisting through mid-morning Sunday. On Sunday,
surface winds will increase again, with gusts up to 30 kts
possible by the afternoon.

Outlook...Widespread light rain is possible late Sunday into
Monday as a slow-moving cold front crosses the area. Ceilings are
forecast to deteriorate following the frontal passage to MVFR over
north- central WI late on Sunday night. Thunderstorm chances will
be isolated.

&&

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

&&

$$

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