NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 261901
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
201 PM CDT Sat Sep 26 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Patchy dense fog is expected to develop over eastern and
  northeast Wisconsin late tonight into early Sunday morning.

- Light rain showers are possible across central Wisconsin on
  Sunday, with better rain chances arriving Tuesday afternoon and
  Tuesday night.

- Trends favor a return to dry weather from Wednesday through
  Friday despite lower forecast predictability.

&&

.DISCUSSION...
Issued at 201 PM CDT Sat Sep 26 2026

Current synoptic pattern and regional weather conditions:
The latest analysis and radar and satellite imagery display
surface high pressure stretching from James Bay to the central
Great Lakes beneath a dominant omega blocking ridge. Low level
winds continue to originate out of the dry airmass within the high
pressure system, resulting in precipitable water values hovering
around 60 to 70 percent of normal. Upstream, shortwave energy
traversing the central Plains is generating light rain across
Minnesota and Iowa where moisture is abundant. This shortwave
energy and deeper moisture will slowly advance toward the western
Great Lakes over the next 36 to 48 hours.

Patchy dense fog late tonight and early Sunday:
High pressure will remain in control across the region tonight,
keeping precipitation chances to our west. The combination of
clear skies and light winds will promote radiational cooling
conditions. This setup is favorable for the development of patchy
dense ground fog over eastern and northeast Wisconsin late tonight
into early Sunday morning. Visibilities may be significantly
reduced in localized areas, so travelers should remain alert for
rapidly changing conditions.

Light rain Sunday and better chances on Tuesday:
As deeper moisture pushes into the dry airmass on Sunday, the
moisture channel will become increasingly narrow. There may still
be sufficient saturation to support light showers and sprinkles
over central and north-central Wisconsin during the morning (20%
chance). High temperatures will be slightly cooler on Sunday due
to the increased cloud cover. A more widespread period of
precipitation is expected from Tuesday afternoon through Tuesday
night, with a 20 to 40 percent chance of receiving a half inch or
more of rain.

Dry weather trends favored Wednesday through Friday:
Forecast predictability decreases considerably from Wednesday
onward due to a large spread in guidance regarding the evolution
of the southern stream system. Despite this uncertainty, current
trends support a higher potential for dry weather returning to the
area from Wednesday through Friday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1156 AM CDT Sat Sep 26 2026

Through 08Z Sun: VFR prevailing across KGRB, KATW, KMTW, KAUW,
KCWA, and KRHI under surface high pressure. Mid and high clouds
will be increasing through this time period as deeper moisture and
cold front move closer to the region from the west. E-SE winds
5-10 kts becoming light/calm tonight.

08Z-14Z Sun: Radiational cooling drives patchy ground fog over
eastern WI. Localized IFR/LIFR vsby < 3SM and < 1SM at KMTW,
KGRB, KATW. NBM indicates 20-30% IFR vsby probability. Clouds
become broken and lower at KRHI, KAUW, KCWA to 2,500-4,000 ft AGL.

After 14Z Sun: Rapid fog burnoff returning all sites to VFR. SCT-
BKN cigs continue at KRHI, KAUW, KCWA with a slight chance of
light showers and sprinkles (under 20% chance). No reductions of
visibility or ceilings expected in any shower activity. Light
variable winds < 6 kts.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC