805
FXUS63 KGRB 301848
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
148 PM CDT Sat Aug 30 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Areas of fog will likely develop again after midnight and could
  become locally dense.

- Seasonably mild and dry weather is expected through Monday night.

- Showers and non-severe thunderstorm chances increase (60-80%
  chance) late Tuesday into Wednesday, with scattered showers and
  unseasonably cool temperatures for late in the week.

&&

.DISCUSSION...
Issued at 146 PM CDT Sat Aug 30 2025

Short Term...Tonight and Sunday

The latest RAP analysis and satellite/radar imagery indicate a
slow moving high pressure system centered across the central
Great Lakes early this afternoon. Weak warm advection generated a
few showers over the arrowhead of Minnesota earlier today, but
these have since fizzled. Otherwise, conditions are quiet across
the region after morning fog and stratus lifted into a fair
weather cloud field by midday. With high pressure centered over
the region for the next 24 hours, the primary focus of the
forecast remains on the potential for dense fog tonight.

Dense Fog: An upper-level ridge will slowly move east and become
centered over the northern Great Lakes tonight, with a sprawling
surface high pressure system remaining in control across the
region. The airmass will remain relatively stagnant due to light
winds. While the airmass will not remain as dry through the column
as yesterday, mostly clear skies and light winds will once again
promote fog formation late tonight into early Sunday morning.
Statistical and probabilistic guidance does not show as strong a
signal for dense fog as it did yesterday, likely due to better
mixing this afternoon. Nonetheless, conditions will remain
favorable for dense fog, particularly over central and north-
central Wisconsin due to the higher elevation and sandy soils. The
fog is expected to lift by 9-10 AM Sunday morning.

Temperatures: Warmer temperatures are expected across far
northern Wisconsin tonight, with lows in the middle to upper 40s.
On Sunday afternoon, warmer temperatures in the middle to upper
70s are forecast across the region.

Rain Chances: On Sunday, weak warm advection will bring in clouds
from the Minnesota Arrowhead into north-central Wisconsin. Models
develop weak instability, and a few convective allowing models
produce light shower activity. However, a significant trigger for
widespread precipitation is lacking, so kept rain chances at less
than 20% near the U.P.-Vilas county border.

Long Term...Sunday Night Through Saturday

Mean upper troughing will establish itself over the eastern half
of the Lower 48 next week. This atypically deep troughing,
combined with the passage of a cold front, will promote showery
weather and well below average temperatures across the Great
Lakes.  One trend observed over the past 24 hours is for
the upper low to be notably slower than previous model runs, with
00Z and 12Z models lingering the upper low near the Great Lakes
through late week rather than lifting it toward Ontario and the
Hudson Bay.

Rain Chances: By Tuesday, models have been persistent with
stronger energy dropping south through the western side of the
trough, reinforcing and deepening the trough for the central and
east-central CONUS. This trough will drop a strong cold front
across the region Tuesday night and Wednesday. Forcing for ascent
looks rather strong, which, combined with instability of 200-400
J/kg, could result in widespread showers and embedded
thunderstorms. However, instability looks insufficient for severe
weather. Beneath the lingering upper low, the weather looks
showery at times from Wednesday through possibly Friday, depending
upon how quickly the upper trough moves across the region.

Temperatures: A very cool airmass will then arrive behind the cold
front with 850mb temperatures falling to around 10 degrees
Celsius below normal by 12Z Thursday. The coldest day appears to
be on Thursday when 850mb temperatures are forecast to be below
the 1st percentile from 06Z-18Z and may approach the
climatological minimum for the date. As a result, high
temperatures on Thursday may approach or fall shy of record low
maximums. The current forecast shows highs ranging from the upper
40s to middle 50s.

Boating Hazards: Conditions will be favorable for waterspouts as
well as small craft advisories at times on Wednesday and Thursday
due to the cold air advection over the relatively warmer waters of
Lake Michigan and Green Bay.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1159 AM CDT Sat Aug 30 2025

Ample boundary layer moisture trapped within a surface high
continues to contribute to scattered or broken areas of fair
weather clouds from 1-3 kft. Ceilings will continue to lift and
scatter out this afternoon.

Light winds and mostly clear skies will persist into tonight as
high pressure continues to influence the regional weather. Once
again, conditions will prove favorable for areas of fog to develop
after 07-08z tonight. Though the signal in guidance is not as
strong as last night, added tempos at AUW/CWA/RHI for 1/2sm
visibilities and bkn002 ceilings. With some mixing today,
confidence is lower than the 18z forecast from yesterday.

The fog and ceilings should lift by mid-morning, which should
evolve into a broken cumulus field over north-central WI (cloud
bases 3-4 kft) but leave good flying weather for the rest of
Sunday elsewhere.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion