989
FXUS63 KGRB 291734
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1234 PM CDT Sun Mar 29 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Mild temperatures expected through Monday. Greatest potential
  for highs in the 60s or even low 70s from central WI to the
  southern Fox Valley.

- Potential for strong thunderstorms with hail exists on Monday night.
  If clearing occurs, strong thunderstorms could also develop
  over east-central WI from early to mid-afternoon Tuesday.

- Potential for winter weather impacts increases Wednesday night
  through Thursday night. There is a 40 percent chance for more
  than 2 inches of snow across northeast Wisconsin during this
  time frame.

&&

.DISCUSSION...
Issued at 1234 PM CDT Sun Mar 29 2026

The latest RAP analysis and satellite imagery show warm advection
continuing across the western Great Lakes ahead of shortwave
energy embedded within northwest flow aloft. A 100 kt jet stream
is providing a steady supply of mid and high-level clouds across
the region so far today, though low levels remain quite dry with
relative humidities generally in the 25 to 40 percent range. A
shallow cold front is currently draped from central Minnesota into
the Upper Peninsula and is expected to sag south through the area
tonight. Upstream, a surface cyclone is intensifying over the
Plains ahead of a low- amplitude upper wave. This system will be
the primary driver for weather impacts in the next 36 to 48 hours
as it migrates toward the western Great Lakes.

Quiet weather will persist through Monday afternoon as the
shallow cold front drops south across the area tonight before
settling over southern Wisconsin on Monday. A significant
temperature gradient is expected Monday, with onshore flow holding
readings in the 40s near Lake Michigan while central Wisconsin
approaches 70 degrees.

Attention then turns to thunderstorm potential Monday night into
Tuesday. A low- level jet is anticipated to point into northeast
Wisconsin by Monday evening, bringing a surge of warm air and
precipitable water values near 200 percent of normal. While a
stout low-level inversion will likely keep convection elevated
initially, steep mid-level lapse rates of 7.5 to 8 C/km and
elevated instability reaching 800 to 1200 J/kg will support
potential for some organized cells. Hail is the primary threat
with these elevated storms, the strongest of which could be
capable of producing hail approaching one inch (severe threshold).

Additionally, light icing (mainly on elevated surfaces) is
possible late Monday night near the Michigan border due to
persistent northeast flow and surface temperatures near freezing.

On Tuesday, as the surface low tracks across southern or east-
central Wisconsin, there is a conditional risk for surface- based
storm redevelopment. If clearing occurs and the low tracks further
north than the ensemble means indicate, a brief window for strong
to severe storms could open during the early to mid- afternoon,
specifically across the Waushara to Manitowoc corridor.

A brief break in precipitation is expected Wednesday as high
pressure builds in, but the pause will be short-lived. Models have
trended faster with a southern stream wave progged to impact the
region Wednesday night through Thursday. Current guidance places
northeast Wisconsin on the cold side of this system, and
confidence in accumulating snow is increasing. Probabilities for
snowfall greater than 2 inches have risen to 40 percent across
northeast WI over the past 24 hours. While the thermal profile
suggests mainly snow, sleet has been introduced to the forecast as
warmer air aloft remains in close proximity to the south.
Significant uncertainty remains, as the 25th to 75th percentile
liquid equivalent range remains quite large (upwards of 0.80
inches!).

Yet another potent storm system is forecast to approach the region
during the Friday night to Saturday timeframe. Unlike the mid-week
system, this feature looks to be much warmer, suggesting a
transition to primarily rain. We will be monitoring this period
for additional thunderstorm potential and the risk for heavy
rainfall as the low- pressure center tracks toward the Great
Lakes.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Sun Mar 29 2026

High confidence in VFR conditions through the TAF period as a jet
stream continues to supply mid and high clouds across the region.
A shallow cold front currently draped across the Upper Peninsula
and central Minnesota will move south across the area tonight,
settling over southern Wisconsin by midday Monday. This front will
bring a wind shift from south or southwest to the northeast or
east.

Winds this afternoon will be gusty at times, generally 15 to 17
kts, before subsiding this evening.

There is some uncertainty regarding low stratus moving inland off
Lake Superior into far northern Wisconsin Monday morning. Have
kept KRHI VFR for now, but later shifts will need to monitor for
potential MVFR/IFR ceilings near the U.P. border.

Outlook...Showers and thunderstorms are likely Monday night into
Tuesday, bringing a increased probability of MVFR/IFR conditions.

&&

.HYDROLOGY...
Issued at 1234 PM CDT Sun Mar 29 2026

No changes to the previous discussion.  The overall threat for
flooding for this week has diminished compared to what it was
looking like a few days ago. The primary driver for this
diminishing trend is the expectation of more scattered, less
widespread rainfall early this week. That said, localized flooding
is still possible where more concentrated storms and heavy rain
occur Monday evening through Tuesday afternoon, especially if
locations impacted still have snow cover. Any higher rainfall
rates with storms could lead to minor flooding in low-lying, poor
drainage and urban areas. Otherwise, the next signal for any river
flooding in latest probabilistic data is not really showing up
until next weekend at the earliest.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC
HYDROLOGY......MPC

NWS GRB Office Area Forecast Discussion