River Flood Warning 15, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
657 AM CDT Sun Apr 12 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Periods of heavy rainfall and thunderstorms expected through the
  middle of the week. Expecting widespread 1.5 to 2.5 inches of
  rain, highest along and south of Hwy 29, where local higher
  amounts in excess of 3 inches could occur.

- A round or two of strong to severe thunderstorms will be
  possible during the early to mid part of next week. The greatest
  (Slight) risk of severe storms occurs south of a line from
  Tomahawk to Oconto to Algoma Monday evening. Hail up to golf
  ball size and damaging winds are the main threats. Additional
  lower probability severe events are possible across central and
  east central WI Tuesday afternoon and evening, and over eastern
  WI Wednesday afternoon.

- Much above normal temperatures expected, with highs in the 60s
  and 70s from today through Friday.

- Minor flooding will continue along the Wolf River through the
  upcoming week. Combined runoff from melting snow in the Upper
  Peninsula and heavy rain will likely result in flooding on the
  Menominee River by Tuesday or Wednesday, with moderate flooding
  in some locations toward the end of the work week and weekend.

- More rain and storms possible Friday into Saturday.

&&

.DISCUSSION...
Issued at 325 AM CDT Sun Apr 12 2026

Showers and embedded thunderstorms were ongoing across the region,
as a H8 warm front and 50-55 knot low-level jet interacted with a
marginally unstable (MUCAPE 400-800 j/kg) and moist (PWATs 1-1.25
inch) air mass. Heavy rainfall was occurring with this activity,
with a few spots in Marathon County already reporting over 1
inch. Isolated stronger cells were likely also producing small
hail. This batch of showers and storms will shift northeast of the
region by around daybreak, but additional storms developing near
the surface warm front along the MN/IA border should expand and
move through the forecast area this morning.

Models show a general decrease in precipitation after the warm
front lifts north this afternoon. The lull continues tonight into
Monday, as H8 flow turns westerly (parallel to the baroclinic
zone), PWATs drop to less than 1 inch and instability wanes.

The front sags south and stalls across central or southern WI
by Monday evening, and provides the focus for another thunderstorm
complex as a southerly low-level jet redevelops, strengthens and
ascends the frontal zone. Instability peaks across the forecast
area Monday evening, with mid-level lapse rates of 7.5-8.5 C/km
and H8 LI's of -4 to -8 C expected. SPC has placed roughly the
southwest half of the forecast area in Slight Risk, with large
hail (up to golf ball size) and damaging winds the primary
threats. If the surface front sets up over the far southwest part
of the CWA, there could be a low-end threat for a tornado, but the
evening timing of the event is not particularly favorable. Heavy
rainfall will also be a concern, especially south of Hwy 29.

After another lull in the precipitation late Monday night into
Tuesday morning, another period of showers and storms is expected
over mainly central and east central WI later tuesday afternoon
and evenings. A lower-end severe threat is possible during this
period, and SPC has placed parts of central and east central WI in
a Marginal risk of severe. Another low confidence severe event
could occur on Wednesday afternoon, but only if the surface low
tracks far enough west for us to get in the warm sector.

See the Hydrology section for information on heavy rainfall and
flooding potential.

Milder temperatures are expected through the period, with highs
reaching into the 60s and 70s from today through Friday.

Medium-range models show another frontal system approaching late
in the week (Friday-Saturday), with potential for additional
rainfall and thunderstorms.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 648 AM CDT Sun Apr 12 2026

Periods of showers and thunderstorms will impact the region this
morning as a warm front lifts north. IFR/MVFR conditions will
occur during this period, but should improve to VFR as the warm
front lifts north this afternoon. Model guidance is less
optimistic with the improvement to VFR, so confidence is on the
low side. Although additional scattered shower activity could
persist this afternoon and tonight, have opted to leave it out of
the forecast. The front is expected to sag back southeast
tonight, so it makes sense that low clouds and at least patchy
fog will spread back in overnight, especially over the northwest
half, where confidence is highest.

Southeast winds will become south to southwest and gust to 25 to
30 knots after the warm front moves through. The winds should
gradually subside this evening, then turn west later tonight.
LLWS is expected to continue through most of the TAF period, most
notably this morning and again tonight.

&&

.HYDROLOGY...
Issued at 325 AM CDT Sun Apr 12 2026

Minor flooding is expected to continue on the Wolf River through
the next week. Even though total rainfall amounts of 1.5 to 2.5
inches, highest along and south of Hwy 29 (with local 3+ inch
amounts), are expected through Wednesday, there will be
significant lulls between each period of heavy rain. In addition,
rainfall amounts over Upper Michigan will be a bit lower (1-1.5
inches) over the regions where a rapid snowmelt is expected to
occur. The runoff from Upper Michigan is expected to bring
minor flooding on the Menominee River by Tuesday or Wednesday,
with possible moderate flooding in spots by the end of the work
week and weekend.

Have opted to hold off on any Flood Watches for the Menominee
River and adjacent tributaries, as HEFS graphics showed a slower
trend with the flooding and lower probabilities of moderate to
major flooding than yesterday.

&&

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

&&

DISCUSSION.....Kieckbusch
AVIATION.......Kieckbusch
HYDROLOGY......Kieckbusch

Hazardous Weather Outlook
National Weather Service Green Bay WI
348 AM CDT Sun Apr 12 2026

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-130900-
Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln-
Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano-
Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago-
Calumet-Manitowoc-Southern Marinette County-
Southern Oconto County-
348 AM CDT Sun Apr 12 2026

This Hazardous Weather Outlook is for north-central and northeast
Wisconsin.

.DAY ONE...Today and Tonight

Heavy rain and scattered thunderstorms are expected this morning.
Potential for severe weather is low, but small hail could occur
with the strongest storms.

Elevated water levels continue along many rivers, with minor
flooding occurring on the Wolf River.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Periods of heavy rain and thunderstorms are expected at times from
Monday evening through Wednesday, and again late in the week. There
is a slight risk of severe thunderstorms with large hail and
damaging winds Monday evening, and a marginal risk in parts of
central and east central Wisconsin Tuesday afternoon and evening.

Elevated water levels will continue along many rivers, with minor
flooding on the Wolf River persisting through next week. Runoff
from rainfall and rapid snow melt in the Upper Peninsula will
likely result in minor flooding on the Menominee River by
Tuesday or Wednesday, with moderate flooding possible during the
end of the work week and weekend.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report any hail or wind gusts greater
than 40 mph to the National Weather Service in Green Bay.

LMZ521-522-541>543-130900-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
348 AM CDT Sun Apr 12 2026

This Hazardous Weather Outlook is for portions of northwest Lake
Michigan and the waters of Green Bay.

.DAY ONE...Today and Tonight

Conditions hazardous to small craft are expected on Lake Michigan
and the bay.

There is a chance of thunderstorms this morning.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Conditions hazardous to small craft will continue into Monday
morning on Lake Michigan.

Thunderstorms will be possible at times from Monday night through
Wednesday, and again late in the week.

Kieckbusch

Preliminary Local Storm Report
National Weather Service Green Bay WI
539 AM CDT Sun Apr 12 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0530 AM     Rain             Oconto Falls            44.87N 88.14W
04/12/2026  M1.71 Inch       Oconto             WI   Cocorahs

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
750 AM CDT Sun Apr 12 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0740 AM     Rain             Underhill               44.88N 88.38W
04/12/2026  M2.10 Inch       Oconto             WI   Public

            Overnight rain total.

&&