NWS-Green Bay Forecast Discussion
FXUS63 KGRB 020340
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
1040 PM CDT Wed Apr 1 2026
Updated aviation portion for 06Z TAF issuance
.UPDATE...
Issued at 809 PM CDT Wed Apr 1 2026
The forecast remains largely on track for the incoming winter
storm. While radar currently shows precipitation increasing
aloft, a layer of very dry air below 750mb is preventing it from
reaching the surface for the time being. Expectations are for
moisture to move in from the south and saturate the lower
atmosphere, allowing precipitation to reach the ground along and
south of the Highway 29 corridor between 1 AM and 4 AM. This
aligns with the start of our current weather headlines for central
Wisconsin and the Fox Valley.
Once the storm begins, precipitation will spread rapidly north and
become heavy at times from late tonight through late Thursday
afternoon. The most notable change in recent data is a colder
trend for surface temperatures(as shown in the NBM). Since the
storm track has shifted slightly southeast compared to yesterday,
it makes sense that warmer air will be slower to arrive.
Consequently, have decided to extend the Ice Storm Warning for
Wood, Portage, and Waupaca counties until 1 PM Tuesday. Freezing
rain is expected to continue through the morning in these areas,
and with forecasted ice totals between a quarter and a half inch,
conditions will be slow to improve. Updated WSW reflecting these
changes will be available shortly.
&&
.KEY MESSAGES...
- A wintry mix of freezing rain, sleet, snow, and rain is
expected, with significant ice and sleet accumulations over most
of central, north central and far northeast WI late tonight
through Thursday. Power outages, tree damage, and extremely
hazardous travel are expected, especially west and north of the
Fox Valley. There will be significant impacts to the Thursday
morning commute regionwide. Ice Storm Warnings, Winter Storm
Warnings, and Winter Weather Advisories have been issued.
- Thunderstorms will also be possible later Thursday afternoon and
Thursday evening, and may become strong to severe in the Fox
Valley and lakeshore areas.
- Heavy rainfall, mixed precipitation, and thunderstorms are
possible Friday night into Saturday. Wintry impacts should be
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 321 PM CDT Wed Apr 1 2026
Dry conditions prevailed across the region this afternoon, with
low clouds coming off Lake Michigan into east central WI, and high
clouds thickening elsewhere. Low pressure was developing over
Colorado, ahead of sharp upper level trough. This strengthening
low pressure system will impact the region with significant sleet
and ice accumulations as it approaches late tonight into Thursday.
The warm sector of this system could reach east central WI,
setting the stage for a brief period of severe thunderstorms
during the very late afternoon and evening.
Winter Weather Headlines Late Tonight into Thursday...Overall,
sleet and ice accumulations have not changed drastically. Still
expect 1/4 to 1/2 inch of ice over the roughly the southwest half
of the forecast area, with 1/2 inch to 1 1/2 inches of sleet over
the far north central and far northeast WI. East winds gusting to
30 to 40 mph may lead to power outages, especially where they
overlap with the heavier ice accumulations. Wintry impacts should
end by 18z/Thu for most areas south of Hwy 8, but temperatures
lingering near the freezing mark over far northern WI will keep
mixed precipitation in the forecast through the afternoon/evening.
Changes to headlines: Start times were delayed by a few hours due
to a lingering dry wedge around 850 mb. In addition, Waushara and
Outagamie counties were upgraded to an Ice Storm Warning, given
expected ice accumulations of two tenths to four tenths of an inch.
Severe Weather Potential late Thursday Afternoon and Evening...
The track of the surface low may bring the warm sector of the
system through east central WI late Thursday afternoon and
evening. While surface based instability is quite weak, MUCAPE
is expected to increase to 300-600 j/kg. Strong shear (0-6 km bulk
shear of 50-65 knots and 0-3 km SRH of 200-300) and strong winds
aloft (850 mb winds of 45 to 55 knots) could make up for the lack
of instability, leading to potential for a bowing line segment
moving through the Fox Valley and lakeshore areas between 6 pm and
10 pm. Damaging winds should be the primary severe threat.
Another Significant Storm Expected Late in the Week...Another
Colorado Low is expected to impact the region Friday night into
Saturday. This system will also bring potential for heavy
rainfall and thunderstorms, and a wintry mix (including possible
significant ice accumulations) over mainly northern WI.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1039 PM CDT Wed Apr 1 2026
Conditions will deteriorate after midnight tonight as a powerful
low pressure system impacts the region. VFR ceilings late this
evening will transition to MVFR/IFR between 06z and 10z as a
wintry mix overspreads the terminals from southwest to northeast.
Expect a prolonged period of hazardous flight conditions through
Thursday morning. Significant icing and sleet accumulations are
likely, especially at RHI, AUW, and CWA, where heavy sleet and
freezing rain will persist longest. A transition to rain is
expected from south to north Thursday afternoon as warmer air
arrives, though IFR ceilings will likely remain through the end of
the period. Some areas from RHI to the U.P. border may remain as a
wintry mix until the end of the TAF period. LLWS is forecast at
all sites tonight through Thursday afternoon with 40-60 kt winds
at 2k ft. Gusty east to northeast surface winds of 20-30 kt will
also persist. Confidence is high in the transition to IFR, but
medium on the exact timing of the changeover from freezing to
liquid precipitation.
With passage of the surface low, there will be a chance of
thunderstorms between 02/23Z-03/03Z across east central Wisconsin.
Have added a prob30 to show the most probable timing. If
thunderstorms develop, gusty winds and small hail will be
possible. While most areas will see rain by this point, areas near
and north of RHI may still see a wintry mix through the evening.
&&
.HYDROLOGY...
Issued at 321 PM CDT Wed Apr 1 2026
Despite the uncertainty in precipitation 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 until 1 PM CDT Thursday for WIZ035>037.
Ice Storm Warning until 10 AM CDT Thursday for WIZ038-045.
Winter Weather Advisory until 10 AM CDT Thursday for WIZ048-049.
&&
$$
UPDATE.........MPC
DISCUSSION.....Kieckbusch
AVIATION.......MPC
HYDROLOGY......Kieckbusch