025
FXUS63 KGRB 101805
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
105 PM CDT Thu Jul 10 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Showers and thunderstorms are possible at times from this
  afternoon through Saturday. Heavy rain and a few strong to
  severe storms will be possible Friday and Saturday.

- 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 18Z TAF Issuance
Issued at 104 PM CDT Thu Jul 10 2025

A scattered cu field, with cloud bases between 2000 and 4500 ft
AGL, has developed this afternoon under widespread high clouds.
Mid-level clouds will gradually shift into the region from the
southwest this afternoon but should stay confined to the central
WI TAF sites. A few showers and perhaps some thunder may accompany
the mid-level clouds this afternoon into this evening for CWA/AUW,
therefore decided to keep a PROB30 group for TSRA. The shower
activity should end late this evening. Some clearing may occur in
portions of central and north-central WI overnight, which may
allow for patchy fog development late tonight/early Friday
morning. Decided to include a TEMPO group at CWA/AUW/RHI for the
MVFR vsbys and potential IFR cigs.

MVFR cigs are anticipated to spread eastward Friday morning with
the potential for additional shower activity. Due to uncertainty
in where and when this shower activity will occur, decided to
include PROB30 groups for only CWA/AUW with this TAF issuance.
Additional PROB30 or TEMPO groups may need to be added for the
east-central WI TAF sites with the next TAF issuance.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......Kruk