839
FXUS63 KGRB 121151
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
651 AM CDT Wed Aug 12 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Scattered storms early this morning, with very small chances
  (10-15%) for additional storms later today. Severe potential is
  low. Chances for showers and storms have increased on Thursday.

- Patchy dense fog early this morning near Lake Michigan and the
  bay.

- Chances for heavy rain have increased this weekend, though
  severe risk remains low.

&&

.DISCUSSION...
Issued at 402 AM CDT Wed Aug 12 2026

Near term through Thursday...Certainly more than we bargained for
early this morning with a slew of warnings issued as there was
just enough lift upon elevated instability and shear over 40 kts.
Hail as large as 1.5 inches was observed in eastern Marathon
County early this morning. Storms have finally faded in intensity
as they shifted into far northeast WI (though small hail and heavy
rain may occur), but some thunder to wake people up early this
morning in the Green Bay area and over Door County. Rest of today,
cannot rule out isolated showers and storms later today into this
evening, but chances remain pretty low. Risk for severe weather
later today has diminished. On Thursday, trend models started to
showing yesterday continues, with pops ramping up to 30-45% as
wave drifts through interacting with daytime heating and some
building instability. Right entrance region of jet will help
enhance activity as well.

Dry for Friday with high pressure overhead, then moderate to
heavy rain expected this weekend. Showers and storm chances
(50-70%) will return to start the weekend as a progressive
shortwave trough moves across the region. Precipitable water
values increase above the 95th percentile ahead of this system,
but seasonably cool temperatures and relatively weak instability
look to limit the severe weather risk. Heavy rain risk is there
though and WPC has expanded the Slight Risk for excessive rainfall
(level 2 of 4) over much of our area south of highway 29. Peak of
rain appears to be Saturday afternoon through Saturday evening.
LREF probability of 1" from this event is up to 25%, but looking
at higher percentiles indicate that the "ceiling" with the rainfall
could be over 2 inches. Also decent agreement it would affect the
urban areas of the Fox Valley and northeast WI. This will have to
be watched as we get closer. Generally drier and seasonable weather
is forecast behind the weekend system.

Temperatures/Fog...Temperatures will be seasonably warm into
Thursday with highs in the lower 80s. Slight cooling into the mid
to upper 70s still pegged for Friday into the weekend. Not a big
cool down by any stretch. In terms of fog, the overnight storms
and blowoff clouds from them did hold down the fog, except near
the lakeshore and closer to the bay/Door County. More patchy fog
could occur tonight, but signal (especially from MOS guidance) is
not as strong as it has looked in the last couple nights.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 650 AM CDT Wed Aug 12 2026

Fog will be main focus this morning, especially from MTW to ATW.
Vsby will be less than 1/2SM at times, especially closer to the
lake. LIFR cigs could linger well into the morning as a weak
boundary is just south of this area of fog. Otherwise, conditions
will be VFR through tonight. Pop-up showers or storms (15-20%) may
occur from northeast WI to the Fox Valley this afternoon into early
this evening. Did not include in the TAFs though as coverage looks
very sparse.

Some fog may occur again tonight, especially at MTW, as light E-SE
winds persist.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion