356
FXUS63 KGRB 102338
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
638 PM CDT Fri Apr 10 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Periods of heavy rainfall and thunderstorms expected from
  Saturday night through the middle of next week. There is a
  85-95% chance of rainfall greater than 1 inch, and a 40-60%
  chance of greater than 2 inches.

- A round or two of strong to severe thunderstorms are possible
  during the early to mid part of next week, with the best chance
  occurring Monday night and Tuesday.

- Minor flooding continues along the Wolf River through the
  weekend.  Combined runoff from melting snow in the Upper
  Peninsula and heavy rain will likely result in more widespread
  and significant flooding next week.

&&

.DISCUSSION...
Issued at 1243 PM CDT Fri Apr 10 2026

The latest RAP analysis and satellite imagery show shortwave
energy traversing the western Great Lakes early this afternoon,
which is pushing a cold front through the eastern Lakes and into
central Illinois. Weak cold advection is noted between this
boundary and high pressure centered over the eastern Dakotas and
southern Minnesota. Cloud cover has been slowly eroding from west
to east across the state this morning as the high builds into the
region. Current observations across northwest Wisconsin show
clearing skies with temperatures in the 30s and 40s. Farther
west, a robust longwave trough is entering the West Coast, which
will act as the primary driver for an increasingly active and
amplified upper-level flow pattern across the central United
States late this weekend and into next week.

Dry weather and a clearing trend will continue this afternoon as
the high pressure system settles across the region. Relatively
light winds and clear skies will promote efficient radiational
cooling tonight, likely leading to minimum temperatures falling
below NBM guidance. Despite the cooling, the arrival of a dry low-
level airmass will limit the potential for fog development. High
pressure will gradually slide east on Saturday, allowing clouds to
increase from southwest to northeast throughout the day. While
the dry airmass should keep conditions dry through mid-afternoon,
saturation in the lowest 2 km will increase after 4 pm across
central Wisconsin. Rain chances rise to around 40 percent by early
Saturday evening as moisture advection strengthens.

An increasingly active weather pattern develops Saturday night as
strong return flow and moisture advection surge into the region.
Precipitable water values are projected to reach the 99th
percentile by early Sunday morning as a 50-55 kt low-level jet
impinges on central Wisconsin. While a strong low-level inversion
will likely keep convection elevated Saturday night into Sunday
morning, these ingredients favor a widespread round of showers and
thunderstorms. Most locations can expect 0.50 to 1.00 inch of
rain during this first round, though stronger convection could
lead to localized amounts up to 1.50 inches. The probability for
rainfall exceeding one inch during this initial period is 40-60%.

The focus for severe weather potential shifts to the Monday night
through Tuesday timeframe. While a cold front is expected to sag
into the region from the northwest on Monday, a temporary lull in
precipitation is possible Sunday night and early Monday as weak
shortwave ridging passes overhead and flow backs to the west.
However, additional height falls and the passage of a surface wave
will trigger renewed rounds of showers and storms. Instability is
forecast to surge during this period, with most unstable CAPE
values reaching 1000-1500 J/kg Monday night and up to 2000 J/kg by
Tuesday afternoon/evening. When combined with deep layer shear of
40-50 kts, conditions will be supportive for organized strong to
severe thunderstorms at times during this period. While the
ingredients are present for strong to severe storms in the
forecast, predictability is generally below normal due to
uncertainty in frontal positions and cloud cover. It`s also
unclear if storms will be surfaced based or elevated in nature. SPC
has outlined areas from central to east- central WI in a 15% risk
outlook for severe weather on Tuesday.

Chances for precipitation will begin to wane on Wednesday.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 638 PM CDT Fri Apr 10 2026

The VFR stratocumulus deck with bases between 4500-6000 ft will
continue to fade across eastern WI late this afternoon with the
loss of daytime heating. Mostly clear skies and VFR conditions are
expected tonight, with only a few additional VFR clouds possible,
mainly across northern WI. Winds will remain light tonight as the
high settles over the region. Despite the light winds mostly
clear skies, dry air in the low levels will prohibit any
widespread fog formation, however, some patchy fog is possible in
a few spots.

On Saturday, mid and high clouds will increase from the southwest
in the morning, with clouds lowering/thickening in the afternoon
as rain spreads northeast across the region, arriving mainly
between 21-01z. Flying conditions will deteriorate to MVFR/IFR in
the evening as the heavier rain arrives. Elevated thunderstorms
are expected at times, especially between 00-12z. Winds will
shift to the south/southeast on Saturday, gusting to 20 kts in the
afternoon/evening.

LLWS is expected to develop late Saturday night into Sunday
morning as a LLJ moves into the region. Another round of showers
and embedded storms is expected Sunday morning.

&&

.HYDROLOGY...
Issued at 1243 PM CDT Fri Apr 10 2026

The cumulative effect of multiple rain events will lead to
significant hydrological concerns by the middle of next week.
While minor flooding continues on the Wolf River today, the
upcoming period from Saturday night through Wednesday carries a
85-95 percent probability of rainfall exceeding one inch, and a
40-60 percent chance of exceeding two inches. Runoff from this
heavy rainfall, combined with rapid snowmelt in the Upper
Peninsula, will likely cause more widespread and significant
flooding. The most significant impacts are currently anticipated
on the Menominee River and its tributaries, where probabilistic
guidance suggests several points could approach moderate flood
stage by Tuesday, April 14. Showers may linger into Wednesday,
April 15, as the upper trough slowly exits the region.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......Bersch
HYDROLOGY......MPC

NWS GRB Office Area Forecast Discussion