444
FXUS63 KGRB 122305
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
605 PM CDT Wed Aug 12 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- There is a low-end (15-20%) chance for showers/storms late this
  afternoon and evening along the HWY 29 corridor. Addtioanl rain
  chances come Thursday.

- Patchy dense fog is possible Thursday morning near Lake
  Michigan and the bay.

- Chances for heavy rain this weekend, though severe risk is low.

&&

.DISCUSSION...
Issued at 142 PM CDT Wed Aug 12 2026

Rest of Today: Surface obs and RAP analysis show a sharp moisture
gradient, with dew points in the middle 50s north and upper 60s
south, extending from the central UP curling back through far
eastern WI and westward through Marathon county. This boundary may
service as the focus for a round of showers/storms this afternoon
and evening, however, forcing is lacking as convergence along the
boundary is weak given light surface winds. Should an isolated storm
or two develop the thermodynamic and kinematic environment would
support a strong and somewhat organized updraft with ~1500 J/KG
MLCAPE and ~50kts of 0-6km shear. The window for any storms to
develop is 3-8PM.

The other focus for tonight is the possible return of fog, mainly
along and near the lakeshore. Light easterly winds will continue to
advect nearly saturated air onshore, so think at least patchy area
of fog are likely near the lake late tonight into Thursday morning.
Confidence in how expansive fog becomes is low due to the placement
of the aforementioned moisture gradient.

Precip Chances Thursday: Another short-wave is progged to pass
through the region Thursday bring another round of scattered showers
and storms the region. CAMs generally show showers/storms pushing
into central WI after 9-10AM Thursday and continuing on and off
through much of the day. The severe risk for Thursday is very low
(less than 5%) as ample cloud cover will limit instability and the
stronger shear is expected to remain over Lake Superior. Main concerns
will any storms will be lightning and locally heavy rainfall. HREF
LPMM does show a few bullseye of 1-1.5" 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 are forecast to track across the state Saturday into Sunday
bring another round of scattered to widespread showers/storms. The
greatest instability is expected to be shunted well south of the
forecast area Saturday limiting the severe potential. However, with
PWATS above the 95th percentile (1.8-2") there is a first for heavy
rainfall and isolated flash flooding, mainly south of HWY 29.
Confidence in the occurrence of heavy rain is low as global ensembles
vary widely with total precipitation amounts.

Next WeeK Outlook: Dry and seasonal weather is expected to start
next week. 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 00Z TAF Issuance
Issued at 604 PM CDT Wed Aug 12 2026

Fog will return again tonight, bringing another period of MVFR to
IFR ceilings and visibilities to much of east-central Wisconsin.
Kept a TEMPO group for the lowest conditions in the mornings, as
fog will likely be patchy at times.

Active weather is expected to pass south of the region on
Thursday, with a few showers on the northern end getting into
central WIsconsin during the morning period. Retained the PROB30
for central Wisconsin at this time, but removed the mention
elsewhere as overall this system has shifted southwards and will
likely have less of an impact on aviation for our area.

&&

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

&&

$$

DISCUSSION.....GK
AVIATION.......Uhlmann