701
FXUS63 KGRB 210643
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
143 AM CDT Fri Aug 21 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Area of showers and embedded storms this morning. No severe
  weather is expected.

- Isolated to scattered storms (40-75% chance) are expected to
  redevelop over eastern WI between 3 and 9 PM today. Strong to
  severe storms are possible (level 2 of 5 risk).

- Showers and storms (40-60% chance) are expected over north-
  central to eastern WI on Saturday.

&&

.DISCUSSION...
Issued at 142 AM CDT Fri Aug 21 2026

Today into Tonight...initial area of showers and isolated storms
was struggling last evening due to dry air, weak/little forcing
and limited instability. An uptick in activity starting around
midnight as slightly better forcing, a LLJ and WAA arrived. This
area of showers and embedded storms will move east across the area
through the morning hours. Main threats will be lightning, small
hail and brief heavy downpours, bringing some much needed rain to
parts of the area. A break in the activity for most spots is
expected later this morning and into the early afternoon, which
will allow the atmosphere to recover and destabilize, with
south/southwest winds ushering in mid 60 to around 70 dewpoints
into much of eastern WI. Highs are forecast to climb into the
upper 70s to around 80, which would produce 1000 to 1500 J/kg of
SBCAPE, with up to 2000 J/kg if a little more sunshine occurs. As
the front arrives during peak heating/instability, another round
of showers and storms is expected to develop, mainly after 3pm.
Deep layer shear is lacking slightly, but has ticked up to 20-30
kts, which would should be enough for some organized strong to
severe storms, mainly between 3-9pm across eastern WI. DCAPEs up
to 1000 J/kg will create a threat for strong downbursts winds in
the strongest cells, with hail possible as well. If discrete
supercells can form, a small tornado risk would materialize. ML
and Neural Network guidance has increased over the last couple of
days, now highlighting eastern WI for a threat for severe weather.
SPC has added a Slight Risk (2 out of 5) for far east-central WI
with a Marginal Risk (1 out of 5) west to around Wautoma and north
to near Marinette. Could also see a severe storm a little further
north. Locally heavy rain will be possible in any storm. If this
were to occur in an urban area, could get some localized flooding.

This Weekend...Northwest, cyclonic flow will prevail across the
Great Lakes. A shortwave trough moving through this flow will
create chances (20-60%) for showers and a few storms across north-
central and northeast Wisconsin on Saturday, mainly during the
afternoon and early evening. Weak deep-layer shear will prevent
significant storm organization, keeping the severe weather risk
low; however, inverted-V soundings and steep low-level lapse rates
would promote some gustier winds and small hail in any stronger
shower/storm.

Next Week...another shortwave trough is forecast to move across
the region late Tuesday into Wednesday, bringing the next chance
for showers and thunderstorms. Instability appears modest with
this mid-week feature, keeping severe probabilities low.

Temperatures into next week will stay fairly close to late-
summer norms, with daily highs mostly ranging from the 70s to
lower 80s and overnight lows in the upper 40s to lower 60s, with a
couple nights with lows in the low-mid 40s across northern WI
this weekend.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 945 PM CDT Thu Aug 20 2026

Main impacts to aviation during this TAF cycle will revolve around
rain/storm potential this evening through Friday afternoon. Rain
chances continue to increase across the central and north-central
sites late this evening, becoming more widespread overnight. Have
included prevailing -SHRA at RHI, AUW, and CWA where rain chances
are greatest, and have followed up with PROB30 group for -TSRA
for late tonight/early Friday morning. SCT showers should then
reach the east-central terminals by late Friday morning. Brief
lull occurs late Friday morning through early afternoon, with TSRA
re-developing (30 to 35% chance) along the cold front over east-
central Wisconsin during peak heating late Friday afternoon.

Cigs lower and thicken to MVFR, potentially IFR, late tonight
with the arrival of the showers. Conditions then improve to VFR
behind the front Friday afternoon.

South winds veer to north/northwesterly by Friday afternoon,
gusting between 15 and 20 knots at times.

&&

.MARINE...
Issued at 142 AM CDT Fri Aug 21 2026

Persistent S/SSW winds will build waves to 2-4 feet on
Lake Michigan late this morning and afternoon. A few 5 foot waves
are possible in the open waters. A few gusts to 25 kts possible
today as well. Conditions look to be just shy of Small Craft
Criteria, so will hold off on an advisory. As winds turn to the
NW this weekend, a few gusts to 25 kts will be possible,
especially near Death`s Door on Saturday.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......Goodin
MARINE.........Bersch