NWS-Green Bay Forecast Discussion
FXUS63 KGRB 211158
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
658 AM CDT Fri Aug 21 2026
Updated aviation portion for 12Z TAF 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 12Z TAF Issuance
Issued at 658 AM CDT Fri Aug 21 2026
An area of showers and embedded storms will continue to move east
through the area early this morning. Mainly MVFR conditions are
associated with this activity, with briefly lower CIGs/VSBYs.
Behind the showers, IFR/LIFR ceilings were developing across
central and northern WI. These clouds will stick around for part
of the morning and slowly lift to a mainly MVFR deck, with other
VFR clouds around as well. As a cold front drops across the area
this afternoon, look for redevelopment of scattered showers and
isolated storms, mainly impacting GRB/ATW/MTW, so have included
TEMPO groups there. Other than a stray shower later tonight, it
looks dry. South/southwest winds up to ~15 kts will shift to the
west then northwest behind the front.
&&
.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.......Bersch
MARINE.........Bersch