168
FXUS63 KGRB 111119
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
619 AM CDT Tue Aug 11 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Chance of showers and storms (30-50%) this morning, mainly
  south of highway 29. Then, a few pop-up showers and storms
  (20-30%) late today far northeast WI. Small chances (25-40%) for
  showers and storms on Wednesday. Severe potential is low.

- Areas of dense fog early this morning near Lake Michigan. More
  dense fog possible late tonight into Wednesday morning region-
  wide.

- Near normal temperatures, then slightly cooler late this week
  into the weekend.

&&

.DISCUSSION...
Issued at 128 AM CDT Tue Aug 11 2026

Shower and storm chances through Wednesday...All eyes on SD early
this morning as this is where the genesis area for storms that
eventually affect WI this morning. Thus far, models are too far
east with main development which is instead focusing farther west
in strongest 850mb warm air advection. Maybe that changes given
the swath of instability that is present from the central Plains
into the Ohio Valley. Right on cue starting to see new development
over far southeast SD. Utilizing the recent runs of the HRRR that
are the better depiction from the CAMs suggests that only the far
south would get clipped with more notable showers and storms this
morning (maximum coverage 9a to noon) with highest pops 30-50%.
There are radar echoes that are over MN with mid-level moisture
and elevated instability, but thus far just a few sprinkles are
making it to the surface. Still appears that even if our area sees
storms, main severe risk will stay south. Later today, pop- up
showers and isolated storms (20-30%) may form over the far
northeast, but better chances may end up in Upper Michigan.

Another potential for showers and storms occurs on Wednesday, but
ensembles have trended toward less of a signal. Favored area would
be northern WI. Similar to the last few episodes, the primary area
of instability remains locked up along main frontal boundary and
closer to nose of LLJ that never makes it this far north. Result
are lower chancy pops (25-40%), but also hints that main activity
could split our area. Perhaps enough overlap of instability up to
1000J/kg and shear over 40 kts during peak daytime heating to
conjure up an isolated severe storm. Based on HREF severe probs
and model QPF, at this point think this risk is on the lower side.

Even smaller chances for showers/storms on Thursday (10-20%),
before high pressure builds across late this week leading to dry
weather Thursday night into Friday. This high eventually shifts
east, allowing the chance for showers and storms to return Friday
night through Saturday night. Early look points to minimal
instability and thus not much risk for severe. Machine learning
output is in agreement with that as well. High pressure builds
back in for Sunday/Monday bringing mainly dry weather.

Temperatures/Fog...Fog along Lake Michigan will be dense this
morning. Moisture and light east flow with nighttime cooling will
is also resulting in patchy dense fog farther inland toward Fox
Valley and over northeast WI. Similar to last night, may need SPS
and/or Dense Fog Advisory. Unlike last night, do have mid clouds
approaching which could cut down on the potential. Will monitor
trends. Another round of fog in store tonight. MOS guidance likes
the potential for locally dense fog yet again. Getting to be that
time of year. Temperatures will be seasonably warm (average highs
now are already starting to slip into the upper 70s central and
north- central) with highs in the lower 80s through Thursday.
Slight cooling into the mid to upper 70s still pegged for Friday
into the weekend. Not a big cool down by any stretch. Does still
appear that Thu night could be chilly up north with lows in the
40s, and with that there will probably be more fog.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 615 AM CDT Tue Aug 11 2026

Marine fog shifted east of MTW as a light west wind developed.
Some light fog at GRB also has abated with arrival of mid clouds.
If winds shift back to the SE today, some more fog could impact
MTW.

Though a few light showers will linger this morning south of
highway 29, expect the bulk of any stronger showers and storms to
stay just south of ATW and MTW. Kept a PROB30 group for TSRA at
MTW, but this may be overdone at this point based on upstream
trends. Most areas will be dry this afternoon, though a few pop-up
showers and storms may try to form in far northeast WI. Despite
the shower and storm potential today, conditions should remain
VFR.

For tonight, expect scattered to broken mid and high clouds. Some
fog may develop again, first at MTW, then at other TAF sites later
in the night. Expect IFR to MVFR vsby with the fog.

Winds will stay light through the period.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion