722
FXUS63 KGRB 040821
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
221 AM CST Wed Mar 4 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Only very small precipitation chances through Thursday night.

- Widespread rain (80-100%) arrives Friday and tapers off
  Saturday morning. Thunderstorms possible Friday afternoon and
  Friday night, especially south and east. Heavy rainfall and a
  few strong storms possible.

- Mild, with highs in the 40s and 50s most days. The warmest day
  occurs on Monday, when some locations reach the middle 60s. Warm
  air flowing across lingering snowpack could lead to fog
  development at times, but especially when higher dew points
  arrive Friday into Friday night.

- Warmer weather may lead to ice breakup on rivers, leading to ice
  jam flooding. Heavy rainfall Friday into Friday night could add
  to the flooding threat. Ice floes could also be a concern,
  especially late in the week.

- Another round of significant rainfall and thunderstorms may
  arrive next Tuesday/Tuesday night.

&&

.DISCUSSION...
Issued at 219 AM CST Wed Mar 4 2026

Mostly clear skies and light winds were observed across the
forecast area early this morning, with temperatures in the middle
20s to middle 30s. Patchy fog was starting to develop over the
northwest half of the forecast area, where deep snow cover
lingered.

Small Precipitation Chances Expected through Thursday night:
Dry weather prevails today, but a short wave and jet streak
ejecting out of the Colorado Rockies may bring a small (20-40%)
chance of rain to our far southern and southeast counties late
tonight into Thursday. Increasing WAA/isentropic lift and
deepening moisture may lead to patchy light rain or drizzle
Thursday night. There is 10-20% chance of light freezing
rain/drizzle in far NE WI.

Friday/Saturday System with Thunder/Heavy Rainfall Potential: The
main system of concern will impact the area Friday into Saturday
morning as a strong low pressure system moves from the central
Plains to the western Great Lakes. Rain is the main concern in
the mild air mass, with thunder expected as elevated instability
(MUCAPE of 300-700 j/kg and 700-500 mb lapse rates of 6.5-7.5
C/km) arrives Friday afternoon into Friday night. Forcing for the
initial surge of widespread moderate to heavy on Friday will be
provided by strong WAA/isentropic lift on the nose of a 35-45 knot
low-level jet, and the passage of an 850 mb warm front. An
additional period of significant rainfall could develop as the
surface low lifts northeast along the cold front Friday night.
PWATs surging to 1.0-1.3 inches across the southeast half of the
forecast area, combined with convective potential, will lead to
pockets of heavy rainfall. NBM probabilities for amounts in excess
of an inch are highest in central WI (60-80%). Could see minor
flooding impacts due to runoff from frozen ground, especially in
conjunction with any ice jam flooding that may be ongoing by that
time. Potential for severe weather is on the low side, as elevated
instability and effective shear are weak, and the elevated nature
of the storms will limit the transport of strong winds aloft to
the surface. There could be a small snow accumulation (less than
an inch) in north central WI late Friday night into Saturday
morning as cold air arrives shortly before the precipitation
ends.

After a generally dry period from Saturday night through Monday
night. another potentially potent frontal system arrives Tuesday
into Tuesday night. This system could bring an additional round of
significant rain and thunderstorms. A surge of colder air changes
the rain to snow late Tuesday night into Wednesday.

Mild Temperatures Followed by a Cool Down Next Week...Much above
normal temperatures are anticipated through early next week, with
highs in the 40s and 50s and lows in the 20s and 30s most days.
The warmest day of the week is expected on Monday, when highs
surge into the middle 50s to middle 60s. Much colder air (near
normal) will return by the middle of next week, in the wake of a
strong cold frontal passage.

Fog potential increases through the week as rising dew points and
melting snow add low-level moisture. The greatest potential should
occur as much higher dew points arrive Friday into Friday night.
Fog development will be most favored over the northwest half of
the forecast area, especially north central WI, where a deep
snowpack remains.

Ice Jam/Ice Floe Potential...In addition to the previously
mentioned potential for runoff flooding from heavy rainfall with
the Friday/Friday night system, there is a lesser threat of ice
jam flooding. The ice jam threat should gradually increase through
the week as warmer temperatures promote some ice break-up. The
ice jam threat will be reduced a bit due to low water levels,
though this could change if the expected heavy rainfall
materializes Friday/Friday night. An increased threat of ice floes
on Green Bay could also develop later in the week, depending on
how strong the Friday/Friday night system is. Wind directions
look favorable for a time from Friday into Friday night, but there
is some question about how strong the winds will be.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1049 PM CST Tue Mar 3 2026

VFR conditions area-wide late evening with mostly clear skies and
light winds. Guidance continues to trend away from fog tonight,
with a much higher probability tomorrow night. Kept a short TEMPO
group in the KRHI, KAUW, and KCWA TAFs early Wednesday morning as
conditions are still supportive of some patchy fog development,
but confidence in this occurring is low.

Expect VFR conditions with mostly clear skies and light winds on
Wednesday.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......KLJ

NWS GRB Office Area Forecast Discussion