NWS-Green Bay Forecast Discussion
FXUS63 KGRB 142105
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
405 PM CDT Tue Apr 14 2026
Forecast discussion for routine afternoon forecast issuance
.KEY MESSAGES...
- There is a risk for strong to severe thunderstorms south of line
roughly from Merrill to Carter to Amberg this afternoon and
evening. Large hail and damaging winds are the main hazards.
There is also an isolated tornado threat mainly 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 flooding concerns in
urban, low-lying, and poor drainage areas 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.
- Additional rounds of rain and thunderstorms are expected at
times Wednesday through this weekend.
&&
.DISCUSSION...
Issued at 405 PM CDT Tue Apr 14 2026
Severe Storm Potential Late This Afternoon/Evening...A surface
boundary (warm front) was orientated west-east just on the
southern edge of the forecast area this afternoon. This boundary
will gradually lift north into the southern portion of the
forecast area this afternoon due to persistent southwesterly flow,
ushering in moist, unstable air. The atmosphere will be primed
across the southern portion of the forecast area with steep mid-
level lapse rates, 50-60 kts of deep-layer shear, and around 1000
to 2000 J/kg of MUCAPE, supporting the potential for severe
thunderstorms with large hail and damaging winds being the main
hazards. However, just along the southern portion of the forecast
area, CAMs and current surface analysis indicate some surface-
based CAPE of 1000 to 1500 J/kg, effective SRH of 100-200 m2/s2,
and steep low-level lapse rates, favoring a tornado threat in
addition to the large hail and damaging winds. After coordination
with SPC and surrounding offices, a Tornado Watch was issued for
Waushara, Winnebago, Calumet, and Manitowoc counties until 10 PM
tonight (Tuesday). Depending on how far north the boundary lifts,
the tornado threat could reach into the next northern tier of
counties. PWATs of 1-1.25 inches are forecast with these storms,
causing a risk of at least additional flooding in urban, low-
lying, and poor drainage areas, and a risk of flash flooding,
especially where ongoing flooding impacts from Monday evening's
storms remain.
Possible Dense Fog Tonight...Following this evening's showers and
thunderstorms, models indicate low-level moisture/stratus
expanding into the area from the northeast. Given the low-level
moisture and the ongoing low-level moisture over the area already,
fog is likely going to occur. Models indicate visibilities may
drop as low as 1/4 mile at times. A Dense Fog Advisory may be
needed late tonight into Wednesday morning.
Rain and Thunderstorms Wednesday-Monday...A surface low is
forecast to lift into the Upper Mississippi Valley Wednesday into
Thursday, bringing another round of rain and possible
thunderstorms. MUCAPE of 200-400 J/kg looks to stay confined to
the southern portions of the forecast area leaving a marginal risk
for severe storms. Although rainfall amounts with this system
look less impressive, any additional rainfall will still add to
the ongoing flooding risk.
A more dynamic trough is slated to impact the region late Friday
into early Saturday, 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. Cooler air
will trail behind this system, which may bring potential for snow
across the far north on Saturday associated with the wrap-around
moisture from the main low pressure system.
&&
.AVIATION...for 18Z TAF Issuance
Issued at 109 PM CDT Tue Apr 14 2026
A mix of MVFR and IFR cigs prevailed across the region early this
afternoon, with the exception of LIFR cigs and 1/4 mile vsbys at
MTW. These conditions are expected to continue until around 00z
Wed. Low stratus with LIFR cigs with fog of 1/2 mile or as low as
1/4 mile will then expand across the area after 00z Wed reaching
all terminals. Anticipate these conditions to continue through
early Wednesday morning before gradually improving by the
afternoon.
Additionally, the next chances for showers and thunderstorms
arrives around 23z at the central and east-central WI TAF sites.
Confidence is highest for thunderstorms at the east-central WI TAF
sites between 23z Tue and 02z Wed, which are expressed with TEMPO
groups. A brief period of LLWS is also anticipated at the east-
central WI TAF sites during this time as well. Lower confidence
for showers and thunderstorms at the central WI TAF sites, so
used PROB30 groups. Some of the strongest storms could produce
large hail and damaging wind gusts.
&&
.HYDROLOGY...
Issued at 405 PM CDT Tue Apr 14 2026
Despite no precipitation falling from this morning through early
this afternoon, several locations across east-central WI were
still dealing with flooding impacts where a maximum of 4.5-5.5
inches of rainfall fell from Monday's storms along an axis from
Stevens Point to Bonduel, with a more broad swath of 1-3" south
of HWY 8. An additional 0.5-1" of rain is expected across east-
central WI this afternoon/evening, 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.....Kruk
AVIATION.......Kruk
HYDROLOGY......Kruk