556
FXUS63 KGRB 261701
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1201 PM CDT Sat Apr 26 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Quiet weekend with moderating temperatures expected.

- A significant severe weather outbreak is possible Monday
  afternoon into Monday night. Most of the forecast area has an
  Enhanced Risk of severe thunderstorms, with parts of central WI
  in a Moderate Risk.

&&

.DISCUSSION...
Issued at 420 AM CDT Sat Apr 26 2025

Skies continued to gradually clear across eastern WI as a short-
wave trough shifted east and Canadian high pressure approached
from the northwest. Temperatures were in the 30s and lower 40s.
Moderate north winds continued in the Fox Valley and lakeshore
areas.

High pressure will bring plenty of sunshine and moderating
temperatures today, with highs in the middle 50s to lower 60s,
except around 50 near Lake Michigan. Clear skies will give way
to increasing clouds over NC/C WI late tonight. Lows should range
from the lower 30s in far NE WI to the middle to upper 30s
elsewhere. Broad WAA will bring mid-level clouds to much of the
region on Sunday, but temperatures should still come up a few
degrees, with highs reaching the upper 50s to middle 60s. A 30-35
kt LLJ will be focused over NC WI in the afternoon, and may
provide enough forcing for a few light showers or sprinkles.

As low pressure organizes in the Central and Northern Plains
Sunday night, south winds will pull Gulf moisture into the
forecast area and the leading edge of elevated instability will
arrive in NC/C WI late. While isolated to scattered showers could
form anywhere in the forecast area, the best chance of showers
and storms is expected across our western counties late. Lows
will mostly be in the 40s.

Potential will increase for a severe weather outbreak Monday
afternoon and Monday night. As the deep low pressure system
tracks northeast from the Plains toward western Lake Superior, a
warm front will push through the forecast area during the late
afternoon and evening. The frontal forcing may generate scattered
supercells in a strongly sheared (0-3 km SRH of 300-500 m2/sec2
and bulk shear of 55 to 70 knots) and increasingly unstable (CAPE
of 1-2K j/kg and mid-level lapse rates of 7-8 C/km) environment.
Storms should take on more of a linear mode (squall line) as a
cold front approaches later in the evening. Severe thunderstorms
with damaging winds, large hail and tornadoes will be possible,
especially during the late afternoon and evening hours. Though the
severe threat may persist into the overnight hours, the threat
should gradually diminish as surface-based CAPE weakens along the
cold front as it shifts east. SPC has placed most of GRB CWA in
an Enhanced Risk of severe storms, with a small part of central WI
in a Moderate Risk.

The threat of storms ends as the cold front shifts east of the
region late Monday night or early Tuesday. Some wrap-around
showers may impact north central WI Tuesday morning. Strong CAA
will result in falling temperatures and gusty NW winds during the
day.

high pressure will bring dry conditions Tuesday night into
Wednesday.

The combination of a low pressure system tracking from TX toward
the Ohio Valley and clipper-type system approaching the western
Great Lakes from Canada will bring a chance of showers to the
region Wednesday night into Thursday night. Potential for phasing
of these two systems later Thursday into Thursday night could
boost the precipitation chances, but this is uncertain at this
time. Dry conditions look to return for next weekend.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1201 PM CDT Sat Apr 26 2025

High pressure is centered over the northern Mississippi Valley to
western Lake Superior late this morning. North flow with
trajectories off Lake Superior continue around the high and across
much of eastern WI. Despite forecast soundings suggesting
otherwise, thermal troughing combined with moisture fluxes off
Lake Superior are favorable for shallow convective cloud
development (cloud bases 3-4 kft) early this afternoon. Ample dry
air above the inversion should support mixing out of the clouds by
2-4 pm.

Middle and high level clouds spread in and lower tonight into
Sunday morning. While lowering, cloud bases will remain VFR even
if spotty light showers approach RHI by the end of the taf period.

Gusty north winds will subside through the afternoon and become
light and variable tonight.

KGRB/KATW...
Scattered to broken convective clouds with bases 3-4 kft will
impact the Fox Valley taf sites through 19-21z before
dissipating. Clear skies will follow into the evening hours before
mid and high clouds arrive from the west and lower overnight into
Sunday morning.

Gusty north winds to 20-25 kts late this morning will subside
this afternoon to under 10 kts after 22z. Light and variable winds
are forecast tonight into Sunday morning.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......MPC