751
FXUS63 KGRB 101137
AFDGRB

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

Updated aviation portion for 12Z TAF 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 12Z TAF Issuance
Issued at 634 AM CDT Thu Jul 10 2025

Calm winds and mostly clear skies have allowed for patchy fog to
persist early this morning. Have decided to briefly carry over
into the 12Z TAFs, though it should burn off quickly following
daybreak. Mid cloud deck then gradually arrives from the southwest
this afternoon out ahead of broken convection ongoing across
southern Minnesota. Opted to continue mention of thunder for the
AUW and CWA TAFs via PROB30 groups where shower/storm activity
appears most likely.

Looking ahead, cigs drop to MVFR, locally IFR, early Friday
morning as steadier precip pushes into northeast Wisconsin.
Localized reductions in vsbys will also be possible where heavier
rain moves over a TAF site.

&&

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

&&

$$

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