453
FXUS63 KGRB 100825
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
325 AM CDT Thu Jul 10 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Next chance for widespread active weather arrives Thursday
  afternoon, continuing into Saturday. Heavy rain and a few strong
  to severe storms will be possible.

- Next round of active weather arrives during the middle of next
  week.

&&

.DISCUSSION...
Issued at 313 AM CDT Thu Jul 10 2025

Broken convection out over western Minnesota continues to outrun
better instability overnight, though skeletal remnants are still
progged to make it to central Wisconsin this afternoon. Clear
skies and light winds have resulted in development of patchy fog
early this morning as lows fall below crossover temps, though
this should quickly burn off by daybreak. Otherwise, expect dry
conditions with increasing cloud cover for the first half of the
day.

Heavy rain potential... Heavy rainfall event still looks to be on
track for the Thursday evening through Saturday timeframe.
Disturbed upper-level regime will result in weak shortwave energy
originating from the Intermountain West interacting with a more
robust vort max digging down from Canada, allowing for northward
transport of deep moisture into the Midwest. PWATs will thus
approach 2 inches (175 to 200% of normal relative to climo) as
rich moisture is allowed to reside within warm cloud depths of ~13
to 14k ft. All of this points toward efficient rain-producing
storm clusters, although north-south precip orientation paired
with shear largely upwards of 20 knots will be a hindrance to
storm residence time/progressiveness. Some questions remain as to
where the axis of heaviest precip will set up, as well as how long
rain lasts into Saturday. Probabilistic guidance continues to be
lackluster in its depiction of heavy rain potential, showing only
a 20 to 30% chance of exceeding one inch of 24-hour rainfall.
Current thinking is that 90th percentile values (~1.25 to 1.5")
would not be out of the question, representing a realistic high-
end scenario. Regardless, it seems a safe bet to assume that
there will be at least localized flooding, especially of urban and
low-lying areas.

Severe weather... Even more questions exist regarding severe
weather potential Friday and Friday night. Cloud debris from
ongoing convection may inhibit better instability during the
afternoon, although CAMs are still picking up on some elevated
instability building along the cold front. This being said, potent
700 mb shortwave should be enough to kick off some convection
during the afternoon and evening, although coverage and intensity
remains to be seen. Best window for any stronger storms would
likely be Friday afternoon and evening over central Wisconsin due
to proximity to the shortwave paired with remnants of diurnal
heating. Inverted-V soundings would likewise support at least a
low-end wind threat. Overall thinking is that Friday`s severe
weather prospect will be heavily influenced by morning convection.

Rest of the extended... The extended forecast sees a transition to
quieter weather as upper flow flattens out, with long-range
guidance not bringing in our next noteworthy precip chances until
mid-week. Temperatures will be relatively steady-state in the 70s
and 80s, until the next cold front traverses the upper
Mississippi Valley on Wednesday.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1059 PM CDT Wed Jul 9 2025

Mostly clear skies and light winds overnight, along with lingering
moisture from recent storms, will result in patchy fog. Greatest
risk of fog is at GRB, ATW, MTW where min temps are expected to
fall below the crossover temps. Have continued to cover the fog
potential (MVFR VSBY) with TEMPO groups from 09z-12z. Mid clouds
gradually increase by afternoon at the TAF sites with potential
for showers and storms moving into central WI by early Thursday
evening. For now, placed a PROB30 into AUW/CWA TAFs where models
are most in agreement scattered showers and storms may be around.

Looking ahead, could be a lull in showers and storms later
Thursday evening with loss of daytime heating and resulting
instability, then more showers and storms may move into central
and north-central WI overnight Thursday night.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......JLA