NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 131750
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1250 PM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Potential for severe thunderstorms with very large hail,
  damaging winds and a few tornadoes has increased for late this
  afternoon and evening.

- Additional rainfall amounts of 1 to 3 inches will occur south
  of Hwy 64 late this afternoon into tonight. Given this area
  already has saturated soils and rising water levels on rivers
  and streams, a Flood Watch has been issued.

- There is a chance of severe thunderstorms with large hail and
  damaging winds south of a line from Wisconsin Rapids to Sturgeon
  Bay during the late afternoon and evening on Tuesday.

- Minor to moderate river flooding is ongoing or forecast to occur
  on several area rivers. Expect many rivers to rise this week due
  to additional rain and runoff from Upper Michigan, with the
  greatest impacts expected on the Menominee River, where some
  locations may see major flooding during the mid to late part of
  the week.

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

&&

.DISCUSSION...
Issued at 314 AM CDT Mon Apr 13 2026

Rain associated with short-wave trough has shifted east of the
region, while a weakening band of showers associated with a cold
front moved through northern WI. Stratocumulus clouds covered
most of the forecast area and post-frontal low stratus was
dropping into northwest and north central WI, but some clearing
was poised to move into central WI. Temperatures were very mild,
in the middle 50s to lower 60s.

Forecast concerns include severe thunderstorms with all hazards,
heavy rainfall and possible flooding later this afternoon into
tonight. Additional severe thunderstorms could clip the southeast
part of the forecast area Tuesday afternoon and evening. River
flooding will also be ramping up regionwide, with the greatest
impacts expected on the Menominee River.

Severe Thunderstorm Potential Later this Afternoon into Tonight:
the cold front currently moving through the northwest part of
the forecast area is expected to set up west to east across
central WI this afternoon. Partial clearing near this boundary
should allow temperatures to rise into the middle to upper 70s
as dew point approach 60 degrees. Surface based CAPE is expected
to increase to around 2000 j/kg near the boundary, with
substantial elevated instability expected farther north due to
steep mid-level lapse rates. CAMs show scattered supercells
developing in central WI during the late afternoon, then
expanding into a large cluster as a strengthening low-level jet
ascends the frontal zone. The initial supercell development
near the frontal boundary in the late afternoon/early evening
could produce very large hail (2+ inch diameter) and possibly a
couple tornadoes, given STP values of 2-3 and 0-1km SRH of
200-300 m2/s2. The greatest potential for tornadic development
looks to be southwest of a line from Wausau to Oshkosh,
including the Marshfield, Wisconsin Rapids, Stevens Point,
Waupaca and Wautoma areas. This impact area may need to be
adjusted if the front sets up farther north or south. North of
the boundary, the main threat should be large hail, given a more
elevated environment, with lower severe probabilities over far
northern WI.

Heavy Rainfall and Flooding Potential late this Afternoon into
Tonight: Have issued a Flood Watch for roughly the southern two-
thirds of the forecast area from late this afternoon through
tonight. This area is expected to receive 1-3 inches of rain
tonight, based on the favored Canadian, Canadian Ensemble mean
and HRRR models. The HRRR is quite ominous, as it shows potential
for significant training of the storms over the southern part of
the forecast area. Much of this region has saturated soils from
the 1-2 inches of rain that fell Saturday night into Sunday, and
several rivers and streams are already running high or flooding.
Additional heavy rainfall could cause significant flooding problems.

Severe Potential Tuesday Afternoon and Evening: The front will get
shoved south by tonight's convection, and will likely set up just
to our southeast Tuesday afternoon and evening. CAMs show strong
to possibly severe convection developing over the southeast third
of the forecast area (roughly south of a ISW-SUE line) between
21z/Tue-03z/Wed. Large hail would be the primary threat, though
damaging winds are also possible.

Additional significant rainfall is expected as a low pressure
system lifts through the area late Wednesday into Wednesday night,
and with a strong cold frontal passage Friday night into
Saturday.

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

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1251 PM CDT Mon Apr 13 2026

Widespread showers and storms will develop late this afternoon
into the overnight hours with MFVR/IFR conditions. Initial
storms may begin to initiate by 21-22Z today, becoming more
widespread this evening. Areas of fog/low clouds will likely
persist into Tuesday.

&&

.HYDROLOGY...
Issued at 314 AM CDT Mon Apr 13 2026

Minor flooding is expected to continue on several area rivers
during the week, and will be exacerbated by periodic heavy
rainfall (starting with tonight's Flood Watch event, which is
detailed above). Runoff from Upper Michigan is still expected to
bring moderate to possibly major flooding on the Menominee River,
especially during the mid to late part of the week. If you live
near a river or stream, keep a close eye on water levels this
week and monitor the latest Flood Warnings from the National
Weather Service in Green Bay.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch from 4 PM CDT this afternoon through Tuesday
     morning for WIZ013-018>022-030-031-035>040-045-048>050-
     073-074.
MARINE...None.

&&

$$

DISCUSSION...
AVIATION...JM
MARINE...
HYDROLOGY...Kieckbusch