729
FXUS63 KGRB 211130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Wed Oct 21 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Dense fog overnight into Wednesday morning across east-central
  Wisconsin and areas west of Green Bay, locally dropping
  visibilities below 1/2 mile. More fog possible early Thursday
  and early Friday.

- Dry and mild through Saturday afternoon with inland high
  temperatures warming into the upper 60s to lower 70s. Warmest
  days Wednesday and Saturday.

- A 20 to 30 percent chance of light rain showers Saturday night
  into Sunday across especially northern Wisconsin. Chances for at
  least some showers are increasing on Monday.

- Cooler early next week, with highs mainly in the 50s.

&&

.DISCUSSION...
Issued at 1044 PM CDT Tue Oct 20 2026

Fog trends through late this week...More dense fog is possible
late tonight into Wednesday morning. Return SW flow is kicking in
just off surface, compared to light E-SE flow last night. Still
with lingering moisture and conditions saturating late tonight,
could see patchy to areas of dense fog. Latest trends not as
pessimistic with visibility perhaps due to the less favorable flow
off the deck, so do not plan to issue Dense Fog Advisory yet, but
will have to watch this overnight. Areas most favored for dense
fog would be near the lakeshore and inland to the west/northwest
of the Fox Valley. High pressure remains overhead until late this
week. A weak boundary moving through tonight will switch winds
back to NE direction late tonight into Thursday morning, which
could lead to slightly better setup for fog with added light flow
off bay and Lake Michigan. Still an onshore wind and cooling late
Thursday night and Friday morning as well, so that spells more
fog. Pattern breaks down Friday night with strengthening SW winds
and warmer nighttime temps.

Dry through Saturday, then at least small chances for showers...
Brush of a northern stream wave is too moisture starved to produce
any rain late today into this evening. Main impact will be the
surface trough/wind shift dropping through. Omega block pattern
will then remain in place the rest of this week. Stronger
shortwave trough shifts across central Canada Saturday, but most
of the lift with this remains over northern Manitoba and Ontario
Canada. Increasing PWATs (toward 90th percentile) pooling along
front tied to the trough may bring a few showers (20-30% chances)
especially to northern WI Saturday night. May see an isolated
shower over rest of the area on Sunday morning, but chances no
more than 10-25%. Chances of some showers on Monday seem to be
trending higher as weekend frontal boundary settles across and
there are signs of tighter low-mid level thermal gradient
(frontogenesis) in right entrance region of jet over the upper
Great Lakes. Based on probabilities of exceeding 0.10 inch, rain
looks pretty light at this point, maybe heading toward a high
POP/low QPF type setup. Deterministic GFS and ECMWF and associated
MOS guidance supporting LREF idea right now as well, and latest
NBM is trending higher as well with 20-40% chances, so confidence
is increasing for at least some lighter showers around.

Cooler early next week: Post-frontal cold advection will usher in
a cooler and more seasonable airmass for Monday and Tuesday as
surface high pressure builds south from Manitoba. This could
really be the case Monday if more clouds and some rain are present
to the north of cold front. Overall daytime highs early next week
will be in the upper 40s to mid 50s, coolest over the northwoods.
Low temperatures will drop back into the low to mid 30s as the
building high promotes ideal radiational cooling at night.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 630 AM CDT Wed Oct 21 2026

Patchy areas of fog are creating pockets of LIFR vsbys across parts
of east-central, northeast, and north-central WI early this morning.
This fog is more of the shallow ground fog variety and should
dissipate rather quickly after sunrise this morning. This will leave
VFR conditions across the region for the remainder of the day.
Another round of fog is possible tonight into Thursday morning,
however, exactly how expansive fog may become is uncertain.

Winds will be light at less than 10 kts through the period.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion