748
FXUS63 KGRB 191708
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1208 PM CDT Sat Sep 19 2026

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Periods of showers and a few thunderstorms will continue into
  tonight. Additional rainfall up to 1 inch will be possible south
  of Highway 29, but the threat for flooding has diminished as
  the heaviest rainfall remains anchored further south.

- A Beach Hazards Statement and Small Craft Advisory have been
  issued into this evening for areas south of Algoma. Additional
  advisories will likely be required from Sunday morning through
  Tuesday as strong northeast winds and high waves develop.

- A quieter and drier weather pattern will settle into the region
  early to mid next week. Patchy frost will be possible at times
  across the northwoods.

&&

.DISCUSSION...
Issued at 122 AM CDT Sat Sep 19 2026

The latest RAP analysis and satellite and radar imagery show a
broad upper-level trough over the western United States with
lower amplitude shortwave energy moving across the Dakotas and
Minnesota. At the surface, a warm front extends from northern Iowa
to central Illinois, with low pressure organizing over Iowa.
A potent 30 to 35 knot low-level jet riding over the warm front
is supporting a line of deep thunderstorms from southeast
Minnesota into southern Wisconsin (south of Wood and Manitowoc
counties) where localized rainfall rates exceed 1 inch per hour.
Because the main convective core remains south of the area, the
risk for flooding across central and east-central Wisconsin has
ended. Over northern Wisconsin, high pressure centered over
northern Ontario and Quebec continues to feed cooler, drier air
southward. This has kept areas north of Highway 10 mostly dry
early this morning.

Periods of rain continue through tonight:
As the shortwave energy and associated surface low move east
across the area today, rain is expected to gradually increase in
coverage from west to east. Broad upper-level ascent in the right
rear quadrant of an upper jet streak combined with low-level warm
advection will generate efficient rainfall production, supported
by precipitable water values in the 90th to 95th percentile.
Additional rainfall amounts of 0.25 to 1.00 inch are expected
generally south of Highway 29 through this evening before the low
exits to the east overnight and brings precipitation to an end.

Quiet weather returns for next week:
For the long term period from Sunday through Friday, a prolonged
stretch of quiet and dry weather is anticipated across north-
central and northeast Wisconsin. Shortwave energy originating from
the western trough will slowly migrate across the central Plains
and southern Great Lakes toward the East Coast during the week,
keeping deep moisture and rain chances suppressed well south of
the local area. Strong high pressure centered over northern
Ontario and Quebec will maintain an expansive plume of dry air
across northern Wisconsin, keeping rain probabilities below 10
percent through Friday. Under clear to partly cloudy skies,
efficient radiational cooling on Monday and Tuesday nights will
drop overnight low temperatures into the mid to upper 30s across
north-central Wisconsin, leading to patchy frost formation in low-
lying areas. A steady warming trend will take place throughout
the week as afternoon high temperatures rise from the low and mid
60s on Monday and Tuesday into the low and mid 70s by Friday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1207 PM CDT Sat Sep 19 2026

Poor flying conditions expected for the rest of the day as low
pressure moves across the region, bringing widespread IFR to LIFR
ceilings, IFR and MVFR visibilities, and periods of rain and
drizzle. There is a 20% chance of thunderstorms this afternoon
mainly south of Hwy 29, but confidence is sufficiently low to
exclude from the forecast.

As low level winds shift to the northeast, improving flight
conditions are expected to return from northwest to southeast
overnight. A return to VFR/MVFR is plausible at all TAF sites,
starting with RHI around 03-05Z and reaching MTW by 09-11Z.

East/southeast winds will be rather steady today, then will shift
to the northeast between 22-02Z. Gusts to 20 kts are expected at
times.

&&

.MARINE...
Issued at 122 AM CDT Sat Sep 19 2026

Gusty southeast winds up to 25 knots ahead of the low will build
waves to 3 to 6 feet along the Lake Michigan shoreline south of
Algoma today. Consequently, the Small Craft Advisory and Beach
Hazards Statement have been extended through 10 PM this evening.
Following a brief lull in winds and waves late tonight, northeast
winds will increase to 15 to 25 knots early Sunday morning
following the passage of the surface low. These strong northeast
winds will persist into Tuesday as a high-pressure system builds
across northern Ontario and Quebec, resulting in building waves of
4 to 7 feet and a high risk of dangerous rip currents along the
Lake Michigan coast. A new Small Craft Advisory and Beach Hazards
Statement will likely be needed from roughly 7 AM Sunday through
Tuesday for waters south of Sturgeon Bay, with additional
advisories likely required for Green Bay and northern lake zones.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 10 PM CDT this evening for WIZ040-
050.
&&

$$

DISCUSSION.....MPC
AVIATION.......GK
MARINE.........MPC

NWS GRB Office Area Forecast Discussion