488
FXUS63 KGRB 020848
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
348 AM CDT Wed Jul 2 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- There is a chance of thunderstorms this afternoon, especially
  over northern WI. A few storms may become strong to marginally
  severe, especially in far northeast WI between 2 pm and 8 pm.

- Additional chances for rain and storms will be possible Thursday
  through the holiday weekend, with the best chance for widespread
  showers and thunderstorms occurring Saturday and Saturday night.
  There should be a break in the thunderstorm chances for 4th of
  July fireworks displays (Friday evening).

- Temperatures will be above normal through the holiday weekend,
  with very warm and humid conditions (heat indices in the upper
  80s to middle 90s) arriving for the 4th of July.

&&

.DISCUSSION...
Issued at 346 AM CDT Wed Jul 2 2025

Clear to partly cloudy skies were observed across GRB CWA early
this morning. Temperatures ranged from the middle to upper 50s
northwest to around 70 southeast. WV imagery showed a short-wave
trough moving through SW Ontario and northern MN, accompanied by a
cluster of showers and embedded thunderstorms. These showers
should reach north central WI toward midday.

Thunderstorm and Severe Weather Potential this Afternoon: The
short-wave over northern MN will track through northern WI this
afternoon, generating showers and scattered thunderstorms. There
will be some ingredients in place for severe weather, including
CAPE of 1-2K j/kg, deep layer shear of 30 to 35 knots and
inverted-V soundings. However, the strongest forcing will overlap
with the lowest CAPE values over northern WI, so overall
confidence in severe storms is low. SPC HREF 40+ dBZ paintballs
and max wind speeds, and simulated reflectivities off the CAMs,
showed the most organized convection occurring in far NE WI, in
the vicinity of a weak convergence zone/surface trough. Will focus
messaging for severe storms mainly over that region between 2 pm
and 8 pm, even though the SPC Marginal Risk covers the entire CWA.
Coverage of the showers and storms should be less farther south
due to weaker forcing. The main area of showers and storms should
shift east of the region by early evening, but models suggest
continued weak development occurring along a weak frontal boundary
as it sags south during the evening and early overnight.

Thunderstorm Chances through the Holiday Weekend: The weak front
is expected to sag southwest of the region by Thursday, then stall
out through Thursday night. Despite a moist and unstable air mass
over the southwest part of the forecast area, models don`t show
much convection developing, likely due to very weak low-level flow
ascending the frontal zone and overall weak forcing. Will only
carry slight chance/chance pops for the southwest CWA during this
period.

The warm front is finally expected to lift northeast through the
forecast area on the 4th of July, though convective coverage will
be limited due to a building upper level ridge over the western
Great Lakes. After the warm front lifts through, generally dry
conditions are expected for evening fireworks displays.

Southwest flow, a stronger short-wave trough and cold frontal
passage will bring a more widespread period of showers and storms
Saturday and Saturday night. Instability (800-1500 j/kg) and deep
layer shear (20-30 knots) will be marginal, and widespread cloud
cover and showers could limit strong to severe thunderstorm
development. PWATs in excess of 2 inches suggest potential for
very heavy rainfall during this period. There is disagreement
on how quickly the cold front will clear the region, but once it
does, there should be a quieter/drier period for at least a day or
two.

Temperatures: Above normal temperatures are expected through
Saturday, followed by near to a little below normal conditions
through the middle of next week. Very warm and muggy conditions
arrive for the 4th of July, with heat indices rising into the
upper 80s to middle 90s during the afternoon. Mild and muggy
conditions will persist through the evening fireworks displays.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1049 PM CDT Tue Jul 1 2025

Good flying conditions with clear skies and light westerly winds
are expected through Wednesday morning. By midday Wednesday, a
scattered cu field will develop with cloud bases around 5000-7000
ft AGL. Scattered showers and isolated thunder are also
anticipated to drop south/southeast during the afternoon. Given
the scattered nature of the convection, continued PROB30 groups at
all TAF sites, except RHI where confidence remains higher. A
brief wind shift from the west to the northwest will accompany
the convection and the potential to produce gusts to 25 kts.
Models are showing signs of another wave of convection tracking
southeast across the area after sunset. With less confidence in
this evolution, have only included PROB30 groups at the central
and north-central WI TAF sites.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......Kruk