Severe Thunderstorm Warning 6, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
701 PM CDT Fri Mar 28 2025

Updated aviation portion for 00Z TAF issuance
and new information added to update section

.UPDATE...
Issued at 640 PM CDT Fri Mar 28 2025

A couple areas of convection were increasing early this evening;
one in association with strong mid-level GFEN forcing in far
northern WI, and another in SE MN/WC WI north of the surface warm
front. The southernmost area of convection was the strongest, as
it was forming where MUCAPE values of 1000-1500 j/kg and deep
layer shear of 45-50 kts existed. A couple of these cells could
produce marginally severe hail as they move through central WI
this evening. Instability drops off a bit farther east, so not
sure if the storms will maintain their intensity as they push
toward the Fox Valley/lakeshore areas.

&&

.KEY MESSAGES...

- There is a 30-50% chance of thunderstorms across the forecast
  area tonight. Some of the stronger storms could produce small
  hail. Isolated hail reports over an inch are possible.

- A significant ice accumulation is possible across north- central
  and far northeast Wisconsin from early Saturday evening through
  Sunday afternoon. There is a 60-90% chance that the area between
  Merrill and Iron Mountain will see at least 0.25" of ice
  accumulation.

- The freezing rain could create significant disruptions in
  travel, along with damage to trees and power outages. Ice Storm
  Warnings and a Winter Storm Warning have been issued for north-
  central and far northeast Wisconsin.

- Precipitation totals are likely (40-70%) to be greater than 1
  inch throughout the event, which could lead to fast flows and
  minor flooding along the shorelines of area rivers and streams
  next week.

&&

.DISCUSSION...
Issued at 233 PM CDT Fri Mar 28 2025

Short Term...Tonight Through Sunday Night

The latest RAP analysis and satellite/radar imagery show low
pressure tracking east across eastern South Dakota early this
afternoon and a warm front extending east from this low to about
Sheboygan. After some morning thunder across parts of central to
east-central WI, precipitation has been relatively quiet through
early this afternoon. Freezing drizzle remained patchy this
across north-central WI this morning where cloud bases didn't get
nearly as low as models forecasted yesterday. As the low tracks
east, the first focus of this forecast remains on thunderstorm
potential tonight. This focus will be followed by a potential ice
storm on Saturday night into Sunday as the next surface wave
tracks along the front.

Thunderstorm Potential Tonight: As low pressure tracks along the
warm front, a strengthening low level jet will lead to increasing
moisture transport and mid-level fgen across far northern
Wisconsin and the Upper Peninsula by early to mid evening. At the
same time, elevated instability upwards of 1000 j/kg will surge
into northern WI above a stout inversion centered at around 800mb.
Combined with precipitable water values above 200% of normal,
ingredients are coming together for a band of showers and storms
developing this evening generally north of a Tomahawk to Wausaukee
line. Effective shears of 40-50 kts and a cold thermal profile
will be favorable for hail. Large hail will be possible in the
strongest cells, particularly those that contain mid-level
rotation. The latest models have increased the amount of
precipitation across the far north and amounts from 0.50" to 1.00"
seem possible.

As the boundary layer cools overnight, minor freezing rain is
possible that could leave a light glaze on surfaces. But
precipitation will be ending as temperatures approach the freezing
mark, so don't think significant icing will be possible. But there
may be just enough for a low end advisory. Road temperatures are
forecast to remain above freezing and that may mitigate impacts
from freezing rain. Will refrain from issuing a Advisory given the
short window and uncertainty about impacts.

Ice Storm Potential: A lull in the precipitation remains expected
on Saturday morning as the front stalls across southern WI and
light precip chances become highest over the southern Fox Valley.
But as upper level flow strengthens and backs ahead of the next
surface low, mid-level fgen will increase again on late Saturday
afternoon through Sunday morning. As has been seemingly advertised
for days, the synoptic setup is very favorable for an ice storm
thanks to a 1030 mb high over northern Ontario feeding in cold air
into the region. Models are becoming in better agreement with the
track of the surface low and position of the freezing line,
thereby increasing confidence where the greatest threat for
significant icing will be located. The narrowing of solutions has
led to an increase of ice accumulations over north-central to far
northeast WI, where the greatest threat is centered. Most of the
freezing rain will fall between 7 pm Sat and 1 pm Sun. The latest
NBM indicates a 40-50% chance of a half inch or more of freezing
rain in a corridor from Rhinelander to Iron Mountain.

Moderate to heavy snow will be possible north of the mixed
precipitation which could result in several inches of snow
accumulations in addition to the ice accumulations.

Some mixed precipitation could make it into the Fox Valley and
lakeshore areas, but that should only fall for a short time on
late Sunday afternoon and evening.

In terms of headlines, the start of impactful icing doesn't appear
to start until Saturday evening as temps fall to freezing and
solar insolation is not a factor across northern WI. That's a
little early for warnings. But considering the increasing
confidence and potential for high impacts, will issue an Ice
Storm Warning for north-central to far northeast WI and a Winter
Storm Warning for Vilas county where 2-4 inches of snow is
expected. This will need to get bracketed by advisories, but will
let later shifts determine where and when to issues those and
leave the Winter Storm Watch in place.

Long Term...Monday Through Friday

Light snow will likely linger across the area on Sunday night that
could lead to a couple inches of snow and prolong the hazardous
travel across the region. After the low exits, below normal
temperatures are expected on Monday and Tuesday.

The next system remains on track to impact the region during the
Tuesday night through Wednesday night. A mix of rain and snow is
forecast with this system and some accumulations appear possible,
particularly over far northern WI.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 640 PM CDT Fri Mar 28 2025

Though the warm front was situated just south of GRB CWA early
this evening, low clouds have eroded in parts of C/EC WI. Farther
north, MVFR/IFR ceilings prevailed. Thunderstorms were developing
over far northern WI, where strong mid-level FGEN was occurring.
Other storms were developing north of the warm front in SE MN/WC
WI, and headed toward C WI. Think all of the TAF sites will have
potential for thunderstorms this evening, but left a mention out
of MTW for now, as confidence is lowest there.

As a wave of low pressure tracks east along the front, showers and
thunderstorms will become more widespread tonight. The showers
should taper off from NW to SE later tonight into early Saturday,
but low clouds, light showers, drizzle and some fog should prevail
through Saturday morning. There could be a brief period of
freezing drizzle across northern WI, including the RHI TAF site,
late tonight into early Saturday, as surface temps drop to around
freezing. Moderate rain will lift north across the area Saturday
afternoon.

Overall, expect MVFR/IFR flight conditions to prevail.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 7 PM Saturday to 7 PM CDT Sunday for
WIZ005.

Ice Storm Warning from 7 PM Saturday to 7 PM CDT Sunday for
WIZ010>013-018>021.

Winter Storm Watch from Saturday evening through Sunday evening
for WIZ030-031.

Winter Storm Watch from Saturday evening through Sunday
afternoon for WIZ073-074.
&&

UPDATE.........Kieckbusch
DISCUSSION.....MPC/MPC
AVIATION.......Kieckbusch

Hazardous Weather Outlook
National Weather Service Green Bay WI
233 PM CDT Fri Mar 28 2025

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-291945-
Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln-
Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano-
Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago-
Calumet-Manitowoc-Southern Marinette County-
Southern Oconto County-
233 PM CDT Fri Mar 28 2025

This Hazardous Weather Outlook is for north-central and northeast
Wisconsin.

.DAY ONE...Tonight

There is a chance of thunderstorms late this afternoon and
tonight. Some of the stronger storms could produce small hail.
Isolated hail reports over an inch are possible.

Slippery travel could develop after midnight across far northern
and northeast Wisconsin due to a light wintry mix.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

Hazardous to dangerous travel is forecast from Saturday night
through Sunday night due to a wintry mix of rain, freezing rain,
sleet, and snow. Significant ice accumulations of a quarter to a
half inch of ice are possible. This would create significant
disruptions in travel, along with damage to trees and power
outages. Ice Storm Warnings and a Winter Storm Warning have been
issued for north- central and far northeast Wisconsin.

The widespread precipitation could lead to fast flows and minor
flooding along the shorelines of area rivers and streams early
next week.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report any freezing drizzle or freezing
rain this morning, and any ice accumulation tonight into the
weekend. Spotters are also requested to report any hail from
thunderstorms.

LMZ521-522-541>543-291945-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
233 PM CDT Fri Mar 28 2025

This Hazardous Weather Outlook is for portions of northwest Lake
Michigan and the waters of Green Bay.

.DAY ONE...Tonight

There is a chance of thunderstorms late this afternoon and
tonight area wide. Some of the storms could contain small hail.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

The probability for widespread hazardous weather is low.

MPC

Preliminary Local Storm Report
National Weather Service Green Bay WI
740 PM CDT Fri Mar 28 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0736 PM     Hail             2 W Plover              44.45N 89.57W
03/28/2025  E0.75 Inch       Portage            WI   Trained Spotter

            Penny size hail in Plover.

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
749 PM CDT Fri Mar 28 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0741 PM     Hail             2 N Arnott              44.48N 89.45W
03/28/2025  E0.75 Inch       Portage            WI   Public

            Report from mPING: Dime (0.75 in.).

0747 PM     Hail             3 E Pembine             45.65N 87.94W
03/28/2025  E0.75 Inch       Marinette          WI   Public

            Report from mPING: Dime (0.75 in.).

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
809 PM CDT Fri Mar 28 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0802 PM     Hail             6 W Beecher             45.58N 88.09W
03/28/2025  E0.50 Inch       Marinette          WI   Public

            Report from mPING: Half-inch (0.50 in.).

&&

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