499
FXUS63 KGRB 262104
AFDGRB

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

.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 323 PM CDT Sat Apr 26 2025

Tonight through Sunday night:

High pressure has moved overhead of Wisconsin this afternoon
keeping conditions dry with light and variable winds. As mixing
has decreased and the winds off Lake Michigan has moved inland
the cumulus deck from this morning has eroded leading to clear
skies. Temperatures have climbed into the low 50s to low 60s
across the region. Clear skies will persist through the evening
and tonight as high pressure begins to exit to our east.

As the high pressure system continues east tonight into Sunday,
a low pressure system will develop in the Rocky Mountain west
and advect toward the state. A mid level shortwave will move
through the flow during this time and traverse Wisconsin Sunday.
This small amount of lift will try to develop some light rain
showers across north central Wisconsin Sunday afternoon.
Soundings show a very dry low level air mass that will likely
prevent most of the rain from making it to the ground. Because
the large dry layer, weak/shallow mid level moisture, and weak
shortwave, capped POPs across the region at 20 to 15%. The best
potential for any isolated/scattered showers to reach the
ground looks to be the far northwest corner of our CWA (north
central Wisconsin). Outside this small chance, everywhere else
should remain dry with partly cloudy skies and highs climbing
into the mid 50s to mid 60s.

Monday through Saturday:

The aforementioned low pressure system that will develop in the
Rocky Mountain west Sunday will advect into the Great Lakes
Region Monday. This low is expected to traverse the central
Plains and move northeast into Minnesota and continue northeast
toward Lake Superior. Southerly winds will set up ahead of this
low and bring some increasing moisture from the Gulf. As the mid
level moisture and instability increases scattered rain is
expected to develop Monday morning. Showers will develop across
western and central Wisconsin during this time.

Heading into Monday afternoon and evening, moisture and lift are
expected to increase. The path of the low pressure system will
bring good chances for wetting rain across the region. Shear
will be great as the low pressure system advances. Bulk shear
remains at least 50 to 55 kts across the forecast area with
values as high as 70 for central Wisconsin. Should the
environment destabilize during the afternoon hours storms are
likely to remain elevated with hail being the main hazard.
Heading into the evening further destabilization is expected
with surface forcing increasing along an advancing cold front.
Storm mode is likely to become linear as this frontal boundary
moves through, however all hazards will be possible. 0-3km SRH
will be good with values around 300 m2/s2 or greater and lapse
rates improving to 7C/km (central Wisconsin could see values
closer to 8c/km). Will have to keep a close eye on surface
conditions throughout the day Monday as this will play a big
roll in whether or not surface based CAPE gets as high as some
models are predicting. Storms are expected to persist after dark
until the cold front has cleared. As we loose diurnal heating
and CAPE after dark storms are anticipated to weaken, but there
are still question on how much they will weaken. Regardless of
the few questions that still remain, the potential for severe
weather remains across the entire forecast area.

Heading into Tuesday morning the severe threat will have ended
for central and northern Wisconsin, but the chances for showers
may linger. The low chance POPs around 20% will continue through
Tuesday morning as the wrap around showers exit to the
northeast. CAA will kick in behind this exiting system leading
to falling temperatures Tuesday and gusty northwest winds. High
temperatures are expected to top out in the mid 40s to upper
50s across the forecast area. Its likely that many areas
(especially north central Wisconsin) will have the warmest
temperatures of the day occurring Tuesday morning and either
sustaining their temps or getting slightly cooler by the
afternoon hours.

High pressure will move back into the Great Lakes Region Tuesday
night into Wednesday. Conditions will remain dry until the next
low pressure system begins to advance toward Wisconsin for
Wednesday night into Thursday. Guidance suggests a low pressures
system in Texas will track northeast into the Ohio River Valley
and a second low will approach from southern Saskatchewan toward
the western Great Lakes. Guidance tries to have these two system
phases together heading into Friday. There is a fair amount of
uncertainty here on where this phasing will occur, but the
short and sweet of it is another round of rain Wednesday night
through Thursday night. Keep up to date on the forecast for
Monday.


&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 323 PM CDT Sat Apr 26 2025

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...
WI...None.
MARINE...None.

&&

$$

DISCUSSION...
AVIATION...
MARINE...