NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 291113
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
613 AM CDT Sun Mar 29 2026

Updated aviation portion for 12Z TAF 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 Monday Night into
  Tuesday. Slower cold front progression opens door to surface
  based storms on Tuesday, especially over east-central WI.

- Active weather late this week into next weekend with potential
  winter weather impacts returning.

&&

.DISCUSSION...
Issued at 251 AM CDT Sun Mar 29 2026

Two main time frames for weather that could lead to impacts this
week. First is of warmer variety with thunderstorms, while the
second is of the colder (and probably unpopular) variety as we
could see return of winter weather impacts.

Warmer through Monday...Today will be the warmest day regionwide
with mainly S to SW winds and not as much thick cloud cover as was
seen on Saturday. Highs will reach the lower 60s central WI to
the Fox Valley, with mainly 50s elsewhere. Lake Michigan shoreline
could stay in the upper 40s. Not completely sunny, but should see
decreasing mid and high clouds this afternoon. Maybe a touch of
fog tonight, then one last warmer day on Monday when locations
from Rapids to Wautoma could be in the lower 70s, while the
highway 29 corridor southward should at least see lower 60s.
Cooler north-central and certainly near the bay and Lake Michigan
as gradient winds ahead of plains low will be from the E-NE. For
those areas, lowered highs closer to NAM/GFS MOS guidance.

Thunderstorms Monday evening through Tuesday...Mid-level trough
crosses northern Plains on Monday with sfc low and warm front
extending to the east. Low-level jet aimed atop the warm front
will transport EML into western Great Lakes. Soundings continue
to show bulk of MUCAPE rooted at 2-3km/800-700mb. Effective MUCAPE
and shear in that layer would still support potential for a few
strong storms with hail being primary hazard. SPC has our area in
the day2 outlook. Agree with previous shift that dry air sub 700mb
could be limiting factor for heavy rain. Consensus increasing
that majority of storms first part of Monday night occur in mid-
level fgen area from north- central to northeast WI, which then
quickly shifts east over lower Michigan deeper into the night.
Secondary wave shifts across late Monday night through midday
Tuesday and this will support another timeframe of showers and
storms. There are model differences in how quick cold front moves
through on Tuesday, and the resulting extent of sfc instability
and severe weather potential. Overall still seems hail and brief
heavy rain would be the primary hazards with storms on Tuesday,
but wind could also occur if the front is slower. SPC has
highlighted our area in new day3 outlook. Cold front eventually
sinks through mid to late afternoon with slowly falling temps,
putting an end to the primary thunder threat.

As a side note, probabilities for any winter weather precipitation
even over the far north remain very low for Monday night-Tuesday
morning (sfc temps too warm to support), then again Tuesday night
and Wednesday morning (main precip will have ended by that time).
Lull in precip continues through early Thursday, then another
system is now agreed upon to start impacting the area later Thursday.

Winter Weather Impacts Possible Thursday and Thursday night...
Deepening trough over western CONUS will help developing a plains
cyclone into the central CONUS by Thursday morning. Growing
consensus that shield of precipitation lifts into the western
Great Lakes on Thursday. Meanwhile, fairly strong sfc high will
still be the northeast. This pattern could favor freezing rain,
ice at times. Most guidance starts precip out as snow and then
changes to rain/freezing rain/snow late Thursday into Thursday
night. WSSI-p picking up on this showing increasing probabilities
of minor, even moderate impacts due to snow and/or ice. NBM v5.0
probabilities of at least 2" snow and/or at least coating of ice
are increasing as well. Early, but does appear where sfc temps are
less than 32f late Thu into Thu night there will be a sharper
cutoff to where temps aloft are warm enough to support freezing
rain versus snow. These details will have to be ironed out, but
enough circumstantial evidence to put a general heads up mention
in this morning's HWO. Beyond this, another system that could
bring more wintry impacts to the region later Friday into
Saturday. Probably not surprising, but winter is not quite done
yet.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 611 AM CDT Sun Mar 29 2026

The primary aviation concern will be LLWS at the eastern TAF sites,
through 14z this morning, then again late this evening and overnight.
Otherwise, light S-SW winds will increase late this morning into
the afternoon, resulting in S-SW winds gusting to 15-18 kts at all
terminals.

VFR will prevail through the end of the TAF period, with broken
mid clouds this morning, and scattered to broken high clouds this
afternoon and tonight.

Outlook...VFR conditions continue during the daytime on Monday. A
frontal boundary moving in from the south will bring increasing
chances for showers and storms beginning later Monday evening.
Conditions will deteriorate to IFR/MVFR by late Monday night.

&&

.HYDROLOGY...
Issued at 251 AM CDT Sun Mar 29 2026

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.....JLA
AVIATION.......JLA
HYDROLOGY......JLA