433
FXUS63 KGRB 141113
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
613 AM CDT Tue Apr 14 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- There is a risk for severe weather south of a Wisconsin Rapids
  to Sturgeon Bay line this afternoon and evening. Large hail and
  damaging winds are the main hazards. There is also an isolated
  tornado threat south of HWY 10.

- Thunderstorms will lead to localized heavy rainfall, greater
  than 1", this afternoon and evening across central and east-
  central WI. This will lead to additional flood concerns through
  tonight.

- 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.

- Addtioanl rounds of rain and thunderstorms are expected at
  times Wednesday through this weekend.

&&

.DISCUSSION...
Issued at 310 AM CDT Tue Apr 14 2026

This morning...

Stratiform rain will come to an end from west to east early this
morning as a LLJ shifts east. Dry conditions will then prevail
through the rest of the morning. Behind the rain areas of fog are
expected to develop across much of the region with the lowest
visibilities, under 1/2 mile, across northern WI.

Severe storm potential late this afternoon/evening...

Last nights MCS has layed-out out an outflow boundary along the WI/IL
border early this morning. Persistent southwest flow south of the
boundary will help lift this boundary north as an effect warm front
through the morning and afternoon. CAMs generally show the boundary
stalling along HWY 21 this afternoon with SBCAPES increasing to
~2000 J/kg south of boundary. This will provide the focus for
convective initiation this afternoon, around 3-5PM. With cloud layer
winds out of the southwest storms will cross over to the cool side
of the boundary as they move into Fox Vally and east-central WI.
This along with straight and elongated hodographs will lead to a
large hail (1-2") threat. A damaging wind threat (gusts up to 60
mph) will also be possible this evening if storms grow upscale.
Tornado threat will primarily be focused across southern WI where
low-level lapse rates will be steeper beneath an eroding EML,
however, any storms that can latch onto the boundary and take
advantage of the increased low-leve shear may pose a tornado threat,
greatest chance would be south of HWY 10. The greatest uncertainty
with the severe threat is the positions of the effective warm front,
as a shift further north or south would change the areas of focus
for severe storms. Convection will also result in localized heavy
rainfall. HREF probs show pockets of 50-70% chances for over 1" of
rain across the central and east-central WI. With on-going
flooding and saturated soils this will exacerbate both aerial and
river flooding concerns.

Rain and thunderstorms Wednesday-Monday...

A surface low is forecast to lift into the western Great Lakes
Wednesday bringing another round of rain and possible thunderstorms.
There is uncertainty with how much instability will be able to
recover from Tuesday evenings convection. Latest CAMs and ML/AI
guidance shunts most of the instability south of the CWA. This would
limit the severe threat, however, there is a 25-30% chance for
another .5" of rain which would cause any ongoing flood concerns to
continue.

A more dynamic trough is slated to impact the region late Friday
into the weekend bringing additional widespread rainfall and storms.
The northward extent of greater instability is somewhat uncertain
with this system, impacting severe weather potential, but this will
be something to watch in the coming days. Drier and cooler weather
is expected behind this system for early next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 613 AM CDT Tue Apr 14 2026

A blanket of LIFR status has developed across much of the region
along with areas of fog creating locally reduced visibility under
1SM. Cigs should gradually rise this morning with most terminals
becoming MVFR by early afternoon. Next round of rain and
thunderstorms will lift into central and east-central WI late this
afternoon (after 4PM). The best chance scattered severe storms will
be south of an ISW to GRB to SUE line with large hail and damaging
wind gusts the main hazards. Once storms depart (after 11PM) another
round of fog and low clouds is expected into Wednesday morning.

&&

.HYDROLOGY...
Issued at 310 AM CDT Tue Apr 14 2026

MRMS QPE from the last 24-hours shows a maximum of 4.5-5.5 inches of
rainfall along an axis from Stevens Point to Bonduel with a more
broad swath of 1-3"  south of HWY 8. The result has been rapidly
rising rivers and streams along with on-going flash flooding. An
additional 0.5-1" of rain is expected across this area today which
will only exacerbate flooding concerns. Runoff from snow melt in
Upper Michigan is also 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...
Flood Watch through Wednesday morning for WIZ022-035>040-045-
048>050.
&&

$$

DISCUSSION.....GK
AVIATION.......GK
HYDROLOGY......GK

NWS GRB Office Area Forecast Discussion