841
FXUS63 KGRB 250408
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1108 PM CDT Tue Jun 24 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Periods of showers and thunderstorms expected Wednesday through
  Thursday night, with heavy rainfall expected. The probability of
  2+ inches of rain is highest (30-60%) over central and north
  central WI. There is a slight risk of excessive rainfall and
  flooding through this period.

- There is some potential for severe thunderstorms over mainly
  central and east central WI Thursday afternoon and evening.

- Much cooler temperatures through Thursday, then a warm-up into
  the weekend.

&&

.DISCUSSION...
Issued at 339 PM CDT Tue Jun 24 2025

The forecast focus remains on heavy rainfall and flooding
potential during the Wednesday through Thursday night period,
and a possible severe weather threat over central and east central
WI Thursday afternoon and evening.

A cold front pushed through the forecast area this afternoon,
accompanied by drier air. Dew points had dropped into the middle
40s to lower 50s in far north central WI, but were still well into
the 60s in the southeast part of the forecast area. Showers in
association with the front have decreased considerably over the
past couple hours, and should continue to diminish through sunset.

Expect a generally dry night tonight as Canadian high pressure
sets up just to our north. A much more comfortable night is
anticipated, with lows in the 50s and lower 60s.

Heavy rainfall/Flooding and Thunderstorm Chances Wednesday
through Thursday Night: Showers and a few embedded storms will
gradually increase from SW to NE on Wednesday, as an 850 mb warm
front lifts north into the region, mid-level frontogenesis
increases, a short-wave trough moves through, and deeper moisture
returns. Most of this rainfall is expected to be light to
moderate, though some heavier pockets of rain could arrive in C/NC
WI later in the day. The 850 mb front will continue to shift
north through the forecast area on Wednesday night, and pockets
of strong frontogenetic forcing will bring increased potential for
heavy rainfall. The best conditions for heavy rainfall may
actually occur Thursday into Thursday night, as an impressively
moist air mass (PWATs of 2-2.25 inches/200+ percent of normal/
near or above climatological max for GRB) move into C/EC WI, a
surface lows moves through and lifts the surface warm front into
the southern part of the forecast area, frontogenetic forcing
continues and a short-wave moves through. Instability also
increases on Thursday, setting the stage for increased convective
input/higher rainfall rates. What is still uncertain through this
period is exactly where the heaviest rainfall will set up. At
this point, the highest probabilities (30-60%) for 2+ inches of
rain remain across C/NC WI.

There is increasing concern for a severe thunderstorm threat on
Thursday afternoon/evening, as the warm front lifts into our
southern counties. If the front makes it, SBCAPE is expected to
reach 1-2K j/kg, with sufficient shear (0-6km bulk shear of 25-40
kts, and 0-3km SRH of 150-300) to support severe storms. Will take
a closer look at this tomorrow.

Rest of the Forecast: Quieter conditions expected, with warmer
temperatures in the 80s arriving for the weekend. A weak cold
front is expected to approach the region Saturday night, then move
through on Sunday, and this could bring a chance of storms.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1107 PM CDT Tue Jun 24 2025

Some isolated pockets of MVFR conditions late this evening with
dips to BKN low clouds a times, otherwise VFR conditions should
persist overnight into Wednesday morning.

Clouds thicken up late Wednesday morning, with rain with embedded
thunderstorms to spread across the area from SW to NE late
Wednesday morning and afternoon. MVFR with localized IFR to occur
as the precip arrives.

Winds will generally be light from the E/NE.

&&

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

&&

$$

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