809
FXUS63 KGRB 290630
AFDGRB

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

Forecast discussion for routine morning forecast 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 06Z TAF Issuance
Issued at 1057 PM CDT Mon Sep 28 2026

Clear skies, light winds, and some high clouds are expected
through Tuesday morning. Patchy dense ground fog/stratus is
expected to develop overnight, with impacts of MVFR to LIFR vsbys
occurring between 09z-13z Tue. Confidence remains highest for the
lowest vsbys occurring at RHI/GRB. Confidence is lowest at
ATW/MTW. Any fog will burn off by mid-morning Tuesday as high and
mid clouds spread over the area ahead of the next rain producing
system. Southerly winds will increase Tuesday afternoon with gusts
of 15-20 kts, highest at RHI. The rain will spread into the area
from the west during the late afternoon, reaching the east-
central WI TAF sites after 00z Wed. Cigs will quickly drop from
MVFR to LIFR at the central and north-central WI TAF sites after
01z Wed with the rain.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion