177
FXUS63 KGRB 131125
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
625 AM CDT Thu Aug 13 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Scattered showers today (20-30%), with a few thunderstorms this
  afternoon (10-20%).

- Dry Friday, then rounds of showers Friday night through Saturday
  night (40-60%). 20-30% chance of thunderstorms late Saturday
  afternoon through Saturday night. Severe weather not expected
  and threat of heavy rain has lowered.

&&

.DISCUSSION...
Issued at 157 AM CDT Thu Aug 13 2026

Near term through Friday: Multiple impulses in NW flow this morning
over the northern Plains. Mid-level warm air advection is supporting
showers into east central MN, ahead of schedule according to 00z
global models/CAMs. Based on upstream trends, expanded low-end
pops over much of the area today, starting as early as 12z over
central WI. Some risk of thunder (10-20%) during the peak heating
of the day, though earlier arrival of showers and thicker clouds
likely holds down intensity. Much stronger signal for stronger
storms is well to the south as yet another MCS tracks along edge
of upper ridge. Main concerns from any storms will be lightning
and locally heavy rainfall. HREF LPMM does show a few bullseye of
1-2" of rain across central WI. These higher end amounts would be
related to any stronger and longer liver storms.

Showers/Storms this Weekend: A progressive upper trough and
surface low with warm front/cold frontal passage are forecast to
track across the state Saturday afternoon through Saturday night
bringing rounds of scattered to widespread showers/storms. The
greatest instability and convergence with low-level jet is shunted
well south of the forecast area Saturday limiting the severe
potential. Despite the presence of PWATs over 1.8" (95th
percentile) farther north, models and ensembles suggest the
heaviest rain risk will also stay to the south. WPC agrees and
has shifted the previous Slight Risk for excessive rain back south
as well. Peak of rain chances will be Saturday through Saturday
evening, with most activity east of the area by Sunday morning.

Next Week Outlook: Dry Monday, then northwest flow brings another
shortwave trough across leading to next chance for organized showers
and some thunder Tuesday. Early look points to lower instability
to support much severe risk, but most Machine Learning output does
show small 5-15% chances with the stronger flow aloft. Beyond
this, as the subtropical ridge builds northeast during the middle
and end of next week a more active pattern may develop across
parts of Wisconsin as a baroclinc zone sets up over the state. Its
way to early to assess any specific thunderstorm threats, but this
will be a time period of monitor, especially for those with outdoor
plans during the second half of next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 624 AM CDT Thu Aug 13 2026

Mid clouds will spread across the area today, and there could be
spotty showers late this morning through the afternoon. An isolated
thunderstorm could also occur during peak heating. Areas of fog
and mist (LIFR to MVFR) from the Fox Valley to the lakeshore will
slowly abate by 14-15z. Light east winds tonight could bring mist
back to MTW overnight tonight with MVFR visibility.

Winds will be light through the TAF period.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT this morning for WIZ045-048-
049.
&&

$$

DISCUSSION.....JLA
AVIATION.......JLA

NWS GRB Office Area Forecast Discussion