083
FXUS63 KGRB 291130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Tue Sep 29 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Patchy dense ground fog will be possible this morning, with
  localized reductions in visibilities to less than one half mile.

- Widespread soaking rainfall is expected over most of the area
  from this evening through Thursday afternoon. Rainfall amounts
  between 1 and 1.5" are forecast across portions of central and
  east-central Wisconsin.

- Patchy frost will be possible at times across northern Wisconsin
  later this week as a cooler and drier airmass settles in.

&&

.DISCUSSION...
Issued at 100 AM CDT Tue Sep 29 2026

Fog potential... Latest surface obs show patchy ground fog
developing over portions of central and far northeast Wisconsin
late tonight as winds decouple and boundary layer saturation
occurs. However, CAMs still not showing a clear signal for dense
fog development into the early morning hours, with equal chances
of manifesting as low stratus as gradient winds increase. Will
continue to monitor trends over the next several hours to see if a
Dense Fog Advisory may be needed.

Heavy rain... Widespread stratiform rain is still on track for
much of northeast Wisconsin tonight through Thursday as upper
low interacts with the remnants of Hurricane Polo to create a
moisture-rich environment from the central Plains into the
Midwest. As such, PWATs increase to around 1.75 to 2" (99th
percentile relative to climo) Wednesday into Thursday as forcing
is maximized along a frontal boundary. Probabilistic guidance
holds steady at a 30 to 60% chance for receiving 2 inches of QPF
during the 48-hour period from Tuesday afternoon through Thursday
afternoon, though this is more of a glancing blow to our southern
tier of counties where better moisture return is. WPC highlights
areas along/south of Hwy 10 in a slight risk for excessive
rainfall on Wednesday, though current thinking is that prolonged
rainfall duration and current drought status would mitigate
flooding concerns in our neck of the woods. Some rumbles of
thunder will be possible at times on Wednesday as MUCAPEs reach
100 to 200 J/kg, though any organized convection is not expected.
If anything, meager instability would aid in higher rainfall rates
during this time.

Extended... Subsidence behind the front will usher in surface high
pressure late on Thursday, which should stick around for the
better part of the extended. As such, expect a pattern shift to
cooler and drier weather, with the exception of 20 to 30% chance
of rain on Saturday. With surface high sitting overhead and
falling temperatures, conditions should be favorable for effective
radiational cooling and frost development at times during the
early morning periods throughout the week. Will continue to
monitor trends for headline potential as we approach the end of
the growing season.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 600 AM CDT Tue Sep 29 2026

Patchy ground fog should continue to scatter out within the next
couple of hours, so have removed any mention of reduced vsbys in
the TAF. Mid clouds then increase from the west later this morning
ahead of widespread rain chances that arrive later this
afternoon. Light rain should make it to the central and north-
central terminals by 00Z Wednesday, spreading to the east-central
sites by around 04Z. Have included PROB30 mentions of -SHRA at all
terminals to account for rain arrival, with prevailing SHRA
beyond. Opted to throw in TEMPO groups for heavier rain with
reduced vsbys at AUW and CWA where better signal exists for higher
rainfall rates. Cigs then quickly fall into IFR, and even LIFR,
territory late tonight into Wednesday morning. Otherwise,
southerly winds increase this afternoon, gusting between 15 and 20
knots at all sites.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......Goodin