NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 011730
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1230 PM CDT Wed Apr 1 2026

Updated aviation portion for 18Z TAF issuance
and new information added to update section

.UPDATE...
Issued at 1214 PM CDT Wed Apr 1 2026

Winter weather headlines seem to be on track. The only change made
this morning was to slow down the start time by a couple hours, as
models are slower to saturate a dry wedge at around 850 mb. Still
seeing some higher ice accumulations in parts of western Waushara
and northwest Outagamie County, so there is some question whether
an upgrade to an Ice storm Warning is needed. Currently leaning
against that idea right now, but still have some work to do on the
forecast.

&&

.KEY MESSAGES...

- A wintry mix of freezing rain, sleet, snow, and rain is expected
  to bring significant ice and sleet accumulations mainly to
  central and northern WI tonight through Thursday. Power outages,
  tree damage, and extremely hazardous travel are expected for
  central and northern WI, with impacts to the Thursday morning
  commute. Ice Storm Warnings, Winter Storm Warnings, and Winter
  Weather Advisories have been issued.

- Thunderstorms will also be possible Thursday into Thursday
  evening, and may become strong to severe in the Fox Valley and
  lakeshore areas.

- Heavy rainfall, mixed precipitation, and thunderstorms are
  possible late Friday into Saturday. Wintry impacts remain
  focused over northern WI.

- Flooding concerns arise this weekend into early next week following
  the passage of the two moisture rich systems.

&&

.DISCUSSION...
Issued at 529 AM CDT Wed Apr 1 2026

Significant Winter Storm Tonight into Thursday...A Colorado Low
brings the next chance for precip tonight through Thursday
evening in the form of all precip types. Although there is still
some disagreement in low track, models have still come into better
agreement with the low tracking northeast from eastern CO to
eastern Upper MI tonight through Friday. This paints the track of
the low moving directly overhead Thursday night. Prior to the low
moving overhead, strong WAA/isentropic lift and f-gen, paired with
an abnormally moist atmosphere (PWATs increasing to 1-1.25
inches) due to surging Gulf moisture, will result in widespread
heavy precip from tonight into Thursday. As the precip lifts
northeast over the area tonight into Thursday morning, surface
temps hovering around freezing with a decent elevated warm layer
would support mainly sleet and freezing rain. The elevated warm
layer will stick around through Thursday, but surface temps will
warm above freezing from south to north late Thursday morning into
Thursday afternoon, causing a switch to all rain. All
precip will come to an end by late Thursday night with the
departure of the low.

Issued an Ice Storm Warning for portions of central WI, where
confidence is highest for ice accumulations of 0.25 inch or
higher. Across the north and far northeast WI, issued a Winter
Storm Warning where a mixture of snow and heavy sleet, combined
accumulations of 1 to 2 inches, and ice accumulations up to 0.25
inch are expected. For locations in east-central WI and along the
lakeshore, issued Winter Weather Advisories as the potential for
significant icing or sleet is lower, but disruptions to travel and
possible power outages remain a possibility. Northeast to east
winds gusting to 30-35 mph across the entire forecast area will
also play a role in potential impacts from icing, including power
outages and damage to trees. The main area of uncertainty is in
the advisory areas with how surface temps will behave tonight into
early Thursday, including road temps, which may stay a little
above freezing, reducing the hazards on roads, and keeping ice
accumulations to mainly elevated surfaces. Another consideration,
area-wide, is the high precip rate, making it harder to have
freezing rain accumulate on surfaces.

By late Thursday afternoon, a chance for thunderstorms will arise
in east-central WI as temps look to warm into the upper 40s to mid
50s. While there appears to be enough instability and shear to
generate a marginal chance of strong/severe storms, the severe
threat will ultimately depend on the exact track of the surface
low and if portions of east-central WI will be in the warm sector.
If these strong storms develop, hail and damaging winds will be
the main threats, along with brief heavy downpours.

Another Significant Storm Expected Late in the Week...Another
Colorado Low is expected to impact the region late Friday into
Saturday. This system will also bring warmer and very moist air to
the region, as the Gulf will still be open. Similar to the
midweek system, there are uncertainties in low track and thermal
profiles, but northern WI appears to have the greatest chance of
having significant wintry impacts with this system, mainly in the
form of freezing rain/icing.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1214 PM CDT Wed Apr 1 2026

MVFR were eroding over NC/C WI, but were holding tough in east
central WI. Given that clearing was noted upstream over central
Lake Michigan, suspect MVFR ceilings should break up in MTW by
mid to late afternoon.

After a period of VFR conditions over most of the area this
afternoon and evening, conditions will deteriorate rapidly as a
mix of sleet and freezing rain overspreads the area from SW to NE
between 06z-10z/Thu. Significant sleet and ice accumulations will
occur over much of the area late tonight into Thursday morning,
before an influx of warmer air at the surface causes a changeover
to rain from south to north. Flight conditions will lower to
IFR over most of the area once the steadier/heavier mixed
precipitation arrives.

Gusty northeast to east winds are expected through the TAF period,
and some LLWS will develop in NC/C WI late tonight into Thursday
morning.

&&

.HYDROLOGY...
Issued at 529 AM CDT Wed Apr 1 2026

Despite the uncertainty in p-types, the two well-saturated
systems this week will lead to flooding concerns, with a signal
for river and stream rises this weekend into early next week
across the forecast area. Minor flooding would likewise be
possible in low-lying and poor drainage areas.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 5 AM to 10 PM CDT Thursday for WIZ005-
010>013.

Ice Storm Warning from 3 AM to 1 PM CDT Thursday for WIZ018>020-
030-031.

Winter Storm Warning from 3 AM to 1 PM CDT Thursday for WIZ021-
073-074.

Winter Weather Advisory from 3 AM to 10 AM CDT Thursday for
WIZ022-039-040-050.

Ice Storm Warning from 1 AM to 10 AM CDT Thursday for WIZ035>037.

Winter Weather Advisory from 1 AM to 10 AM CDT Thursday for
WIZ038-045-048-049.
&&

$$

UPDATE.........Kieckbusch
DISCUSSION.....Kruk
AVIATION.......Kieckbusch
HYDROLOGY......Kruk