666
FXUS63 KGRB 142304
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
604 PM CDT Tue Apr 14 2026

Updated aviation portion for 00Z TAF 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 00Z TAF Issuance
Issued at 603 PM CDT Tue Apr 14 2026

A warm front remains stationary across the southern Fox Valley to
near KVOK this evening. Scattered strong to severe thunderstorms
will continue to track east-northeast along and south of this
boundary, primarily impacting areas south of a KAUW to KMNM line
through 03z. The greatest risk for severe weather, including large
hail and gusty winds to 50 knots, will be focused south of a KISW
to KGRB line.

Behind the departing precipitation, low-level moisture will surge
into the region from the northeast. Expect flight conditions to
deteriorate rapidly to IFR and eventually LIFR/VLIFR at all
terminals overnight. Widespread fog is anticipated, with
visibilities dropping to 1/4SM in many locations. Confidence is
high that these poor flight conditions will persist through
Wednesday morning.

Improvement will be slow on Wednesday. While ceilings and
visibilities will lift first over north-central Wisconsin (KRHI),
persistent MVFR ceilings are expected to linger across the rest of
central and east-central Wisconsin through Wednesday afternoon.

Low-level wind shear may also develop at KMTW tonight with 40
knot winds forecast at 2000 feet between 03-06z.

Outlook: Another round of showers and thunderstorms is possible
Wednesday night, mainly across central and east-central Wisconsin.

&&

.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.......MPC
HYDROLOGY......Kruk

NWS GRB Office Area Forecast Discussion