713
FXUS63 KGRB 160007
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
707 PM CDT Sat Aug 15 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Scattered showers (50 to 80%) and isolated storms (10 to 30%)
  will be possible later this afternoon into this evening, and
  again Sunday afternoon. Most areas should remain dry.

- Better chances for more widespread rain and storms will be
  Tuesday into Wednesday. Locally heavy rain will be possible,
  though confidence in severe weather is low.

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

&&

.DISCUSSION...
Issued at 1200 PM CDT Sat Aug 15 2026

Rain/storm chances... Dry trend persists early this afternoon as
dewpoints continue to mix out across the forecast area. As such,
radar shows the bulk of the rain remaining off to our south where
better jet dynamics and moisture transport reside. Best chances
for showers and thunder in our neck of the woods look to be later
this afternoon and evening as transient shortwave and weak warm
front move over Wisconsin. Modest instability (500 to 800 J/kg
MLCAPE) coincides with PWAT max approaching 2" during this time,
which should be enough to get some showers popping as upper jet
organizes to the north. Excessive rainfall potential will be
minimal due to lack of instability and spotty shower coverage,
with NBM probabilistic guidance only showing a 10 to 25% chance
for receiving 0.5" of QPF over our southern tier of counties.
Localized amounts of 0.5 to 1" would not be out of the question,
though would likely only come with repeated showers.

Diurnally-driven shower/storm chances will return Sunday
afternoon as cyclonic flow remains and remnant shortwave energy
departs to the east. Windows for clearing should allow for decent
instability (~1,000 J/kg) to build mainly from the Fox Valley
east, which is represented by chance (20 to 30%) PoPs. Showers and
storms should remain isolated to scattered in coverage.

Extended... Tuesday and Wednesday feature the best chances for
widespread rain and storms as potent trough deepens over the
Hudson Bay and cold front digs south during peak heating. Cursory
glance shows decent instability in proximity to the front
coinciding with 30+ knots of bulk shear, which would suggest the
possibility of strong storms developing Tuesday afternoon. ML
guidance, and thus SPC outlook, show the main severe threat off
to our southwest, though trends have been shifting northward. WPC
ERO likewise highlights areas along/south of Hwy 29 in a Day 4
slight risk for excessive rainfall due to skinny CAPE profiles and
potential for backbuilding storms. Regardless, will bear watching
as details come into focus in the next couple of days. Cooler and
more stable air then filters in behind the front on Wednesday,
with temperatures settling mainly in the 70s. Highs should read
near normal through most of next week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 707 PM CDT Sat Aug 15 2026

Primarily VFR conditions across the region this evening, however, an
area of scattered showers develop in in and east of the Fox Valley
is producing scattered MVFR cigs. Cigs will gradually lower across
much of the region tonight ahead of a cold front that is currently
pushing through far northeast MN. As the front works across the
region tonight, between 3-10Z, additional scattered showers are
expected along the front. Most confidence that these showers will
impact RHI with lower confidence that they will hold together
further south and east. Behind the front a few hours of IFR cigs
are expected Sunday morning across much of the region with cigs
rising from south to north through the morning.

Prevailing southeast winds gradually veer to northwest by late
Sunday morning as the front passes through.

&&

.MARINE...
Issued at 1200 PM CDT Sat Aug 15 2026

Gradient winds increase slightly out of the southwest this
afternoon as a frontal boundary approaches from the west. This
will result in conditions hazardous to small craft along the
nearshore waters of Lake Michigan, mainly south of Two Rivers.
Gusts to 20 knots and waves up to 4 feet will be possible.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......GK
MARINE.........Goodin

NWS GRB Office Area Forecast Discussion