454
FXUS63 KGRB 150550
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1250 AM CDT Sat Aug 15 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Rain chances continue to trend lower today (15-30%). Many areas will
  stay dry. Scattered showers (30-70%) and a few thunderstorms
  (10-20%) tonight as cold front moves through.

- Pop-up showers (20-30%) and storms Sunday afternoon from Door
  County to the lakeshore.

- Next chance for showers and some storms (60-80%) Tuesday and
  Tuesday night, tapering off Wednesday morning.

- Turning cooler middle to end of next week, with highs in the
  lower 70s.

&&

.DISCUSSION...
Issued at 1250 AM CDT Sat Aug 15 2026

Near term through tonight: Dry trend for today continues. For most
of the day, organized showers and storms will have hard time making
it even into southern WI as gradient of instability and convergence
from low-level jet remain south. Moisture advection on north edge
could result in a few showers over far southern areas, but most
locations will stay dry through late afternoon. Even so, mid clouds
will hold down temps in the upper 70s to near 80. A few more showers
and maybe a storm could develop over central WI late this afternoon
as lift from shortwave moves in from central plains and interacts
with CAPEs up to 500J/kg along a warm front. Better chances for
showers and isolated storms occurs this evening into the overnight
as tail of shortwave over Lake Superior and cold front cross the
state. Right entrance region of jet will also help organize
showers, especially over northern WI, where some rain is certainly
needed. Even as PWATs near 1.8 inches (95+ percentile) will be
interacting with the forcing, rainfall amounts look on the light
side with minimal instability. If a heavier swath of showers
develops it could produce over 0.5 inch of rain over north-central
WI, but that prospect looks quite localized. Signal is there that
not much rain at all makes it into northeast or east-central WI
where HREF means showing a min in QPF.

Pop-up storm chances Sunday: Despite being behind the front on
Sunday, shortwave dragging through during peak heating may kick
off isolated showers and storms over from Door County to along the
lakeshore in the early afternoon. Not a lot for pops (20-30%),
but CAPEs over 1000J/kg boosted by lingering higher dewpoints
and effective shear over 30 kts could produce a stronger storm.

Next chance for rain is Tuesday into Wednesday: Sharpening northwest
flow pushes stronger shortwave and cold front across the western
Great Lakes region. Though forecast instability and various
Machine Learning output suggest highest signal stays southwest
from southern MN into IA, it will not take much increase in CAPE
to lead to some severe threat across WI as the forcing arrives
during peak heating on Tuesday afternoon. Uncertainty on how fast
this system exits and models are not surprisingly showing some
variability with that. Overall, other than tonight`s shower
chances, this system looks like the greatest opportunity for
rain next week. Cooler air push behind this system remains on track,
with highs settling into the lower to middle 70s Wednesday through
Friday.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1036 PM CDT Fri Aug 14 2026

Cloud cover will gradually increase overnight as a surface boundary
currently parked along the I-94 corridor begins to lift north. Cigs
should remain VFR through the morning, but a few pockets of MVFR
cigs are possible across the Fox Valley Saturday morning. There is
also a small chance (20-30%) for some scattered showers to develop
across central into east-central WI early Saturday morning, however,
with limited instability and weak forcing the risk for any lightning
is low. Low end VFR cigs are expected to overtake much of the region
by Saturday afternoon. A cold front sweeping across the region
Saturday will bring another (40-60%) for scattered showers from west
to east after 03Z. Confidence that any showers would impact a
terminal before the end of the TAF period was too low to include in
the TAFs as this point but will likely need to introduce at least
SHRA with future issuances.

Light east to southeast winds are expected tonight. A slight
increase in the southeast winds is expected Saturday with occasional
gusts up to 15 kts during the day. Behind the passing front Saturday
night winds will veer around to the west northwest.

&&

.MARINE...
Issued at 1250 AM CDT Sat Aug 15 2026

Southeast winds will increase today across the Lake Michigan
nearshore waters as a cold front approaches the area. This will
bring Small Craft Advisory conditions, with gusts over 20 kts and
waves up to 4 feet, highest south of Kewaunee.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from 8 AM CDT this morning through this
evening for WIZ040-050.
&&

$$

DISCUSSION.....JLA
AVIATION.......GK
MARINE.........JLA

NWS GRB Office Area Forecast Discussion