585
FXUS63 KGRB 210753
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
253 AM CDT Thu Aug 21 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Patchy fog, locally dense, is expected this morning, especially
  over central and north-central Wisconsin.

- Dry conditions persist through Friday morning, with rain/storm
  chances arriving Friday afternoon. An isolated severe storm
  will be possible.

- Temperatures fall to well below average this weekend, lasting
  into next week.

&&

.DISCUSSION...
Issued at 252 AM CDT Thu Aug 21 2025

Short Term...Today Through Friday Night

Patchy dense fog will continue this morning before dissipating
after sunrise as high pressure remains across the Great Lakes.
Some afternoon cumulus clouds are expected as dry conditions
remain across the region. Highs today should generally be in the
middle to upper 70s.

Tonight should remain dry as the high sinks southeast. Return flow
on the backside of the high and increasing clouds will keep
temperatures fairly mild tonight as temperatures only fall into
the upper 50s to lower 60s. Fog is not expected to be as
ubiquitous overnight into Friday morning as HREF probabilities of
visibilities less than 0.25 miles are 20-40% across central and
east-central Wisconsin west of the Fox Valley as well as a less
robust signal for fog in general from the hi-res models.

A cold front will track through the region Friday afternoon into
Friday night, bringing showers and thunderstorms as it passes
through the area. Given the later arrival of the front, highs on
Friday will still rise into the upper 70s to lower 80s. SBCAPEs
ahead of the cold front are forecast to rise to 1000 J/kg north
and west of the Fox Valley along with 20-25 knots of effective
shear. The combination of instability, shear, and timing of the
front means some storms could be strong to severe with gusty wind
and large hail. CAPE profiles are long and skinny Friday afternoon
and evening, indicating the severe threat would be fairly
isolated.

Long Term...Saturday Through Wednesday

Temperatures... Main story for the long-term leg of the forecast
centers around the arrival of fall-like temperatures this weekend
as northwest flow regime sets up over the Midwest. Cold FROPA on
Saturday will usher in a much cooler and drier airmass across
northeast Wisconsin starting on Sunday, tanking temperatures into
the 50s and 60s for most. 850 mb temperatures approach 0C as
well, which, when paired with subsidence from high pressure, may
result in further cooling trends in the coming days as shorter
range models come into play. NBM 25th to 75th percentile guidance
only shows a few degree spread in high temperatures during this
time, lending to a higher confidence forecast. Additionally, the
ECMWF EFI paints a widespread area with 70 to 80% of members below
model climo through the middle of next week.

Precipitation... Scattered showers will be possible on Sunday
within remnant cyclonic flow from departing low pressure. A
diurnal shower or two may linger into Monday as additional
shortwave energy pivots over the Great Lakes and low-level lapse
rates steepen. Otherwise, long-range guidance shows a consistent
signal for below average precip as Canadian high pressure
influences much of the eastern CONUS.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1048 PM CDT Wed Aug 20 2025

Stubborn high-end MVFR and low-end VFR clouds slowly eroded
through the evening hours, but they may start to fill back in or
expand overnight. Still some uncertainty regarding fog development
tonight as just how fast clouds clear out and if/where any
additional low stratus will redevelop will determine how
widespread/dense the fog will become. Probabilities of a half mile
or less VSBY is higher than last night, mainly between 20-60%
(highest across north/west of the Fox Valley). Have dropped the
prevailing VSBYs a little, and will continue with the TEMPO
groups for the overnight and early morning fog, with the LIFR at
RHI. Any fog will burn off and lift Thursday morning, with some
lingering stratus and daytime cu expected. Winds will remain light
through the TAF period.

&&

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

&&

$$

DISCUSSION.....Kurimski/Goodin
AVIATION.......Bersch