671
FXUS63 KGRB 171837
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
137 PM CDT Thu Sep 17 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A period of heavy rainfall is expected Friday afternoon through
  Saturday, with the heaviest rain occurring Friday night. A 30 to
  50 percent chance of rainfall exceeding 2 inches exists roughly
  south of Highway 29.

- A quieter and drier weather pattern will settle into the region
  early to mid next week.

&&

.DISCUSSION...
Issued at 137 PM CDT Thu Sep 17 2026

High pressure will keep the weather dry across the region tonight.
Lingering low level moisture may cause some fog across far north-
central Wisconsin late tonight into early Friday morning, mainly
north of highway 8. Meanwhile, clouds will increase late tonight
into Friday morning ahead of the next low pressure system slated
to affect the region later on Friday through the weekend.

The trend with the heaviest precipitation continues to trend south
this run, with the swath of moderate to heavy rain in southern
Wisconsin this run Friday and Saturday. This scenario makes sense
as the best instability stays to our south, limiting the
potential from heavy rain due to thunderstorms. There is a
continued interesting trend with the GFS in a band of rain across
north-central Wisconsin Friday afternoon associated with mid
level frontogenesis. Model soundings indicate quite a bit of dry
air along with a lack of instability as this area of frontogenesis
tracks through northern Wisconsin. Therefore, even if this area
does end up developing, the impact shouldn`t be high as the area
is heavily forested and currently in a drought. Meaning any rain
would be welcome and soaked in by the soil.

Confidence in heavy rainfall across our area has continued to
trend south, with the probability of 2 inches or more falling
to 30 to 50 percent mainly south of highway 29. Although the trend
continues to dive south, the ECMWF still brings the swath of
moderate to heavy rain through central and east-central Wisconsin
Friday night. Therefore, the heavy rain staying to our south isn`t
a certainty at this point. Rainfall should for the most part end
by late Saturday, with light rain possibly continuing Saturday
night into Sunday.

Shortwave energy from the western North American trough will
slowly migrate east over the center of the country through the
middle of next week. The associated low pressure system and
rainfall footprint have trended further south over the past 24
hours. Therefore, it appears that the bulk of the precipitation
will remain south of the region. Only small chances of rain, up to
30 percent, are forecast for Monday. For the remainder of the
week, strong high pressure settling over northern Ontario looks to
funnel ample dry air southward across northern Wisconsin. Rain
chances are expected to remain low for much of next week under the
influence of this Canadian high.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1200 PM CDT Thu Sep 17 2026

Despite rain exiting the region this morning, MVFR/IFR conditions
continue to plague the TAF sites early this afternoon as low level
moisture remains across the region. Models and satellite data
indicate dry air should eventually scatter out these low clouds,
leaving VFR conditions in its place. Further north, these
conditions may stick around a bit longer as these are diurnally
driven but should dissipate once the sun sets.

High pressure will build in across the north tonight, bringing
primarily VFR conditions to the region. Some patchy fog is
possible across north-central Wisconsin, mainly affecting the KRHI
TAF site with MVFR/IFR conditions.

Mid and high clouds will increase late tonight ahead of an
approaching low pressure system taking aim for the region on
Friday. Although many of the lower conditions and impacts will be
Friday afternoon, conditions are expected to fall to IFR with
light to moderate rain through Friday night.

&&

.MARINE...
Issued at 137 PM CDT Thu Sep 17 2026

Gusty easterly winds ahead of and during the passage of the
aforementioned low pressure system will build wave heights
significantly on Lake Michigan from Friday night through the
weekend. This will create hazardous conditions for small craft and
increase the risk for dangerous rip currents along area beaches
from late Friday night through the weekend and possibly into
Monday.

&&

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

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kurimski
MARINE.........Kurimski

NWS GRB Office Area Forecast Discussion