187
FXUS63 KGRB 091138
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
638 AM CDT Wed Jul 9 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Next chance for widespread active weather will be Friday into
  Saturday. Heavy rainfall and a few strong storms will be
  possible with this system.

- Another round of active weather may be possible around the
  middle of next week.

&&

.DISCUSSION...
Issued at 452 AM CDT Wed Jul 9 2025

Patchy fog...
Low level moisture has pushed in a low stratus deck early this
morning, accompanied by some patchy fog at the surface, mainly
across portions of north-central Wisconsin. This low stratus deck
will likely curb our morning temperature rise, but cloud cover is
expected to dissipate again by the early afternoon, with clear
sunny skies by the evening.

End of the Week Precip...
Attention then turns to the next approaching weather maker Friday
and Saturday. An initial surge of warmer air aloft and
accompanying moisture plume could push showers into portions of
central Wisconsin as early as the morning hours on Friday, but
better organization likely won`t arrive until a mid-level
shortwave crosses into the region during the afternoon. This 700mb
shortwave should support at least some convection through the
afternoon and evening, but the overall strength of convection
remains uncertain. The potential early arrival of rain may inhibit
some of the better instability, but model soundings do show
potential for some elevated instability by the afternoon as the
surface warm front gets into southern Wisconsin. Probabilistic
guidance continues to keep severe potential relatively low,
suggesting around 5 to 15% probabilities for the region. If any
stronger storms were to form, the most likely timing would in the
late afternoon to evening hours, before weakening again overnight
with the departure of the shortwave. How long rain sticks around
into Saturday remains uncertain as of this forecast as well, with
models like the ECMWF and GFS suggesting a prolonged rainy period
as an upper jetstreak crosses the area early Saturday, possibly
sustaining any showers a bit longer.

All things considered, the main concern with this system will be
heavy rainfall. PWATs push to around 2-2.3 inches through the
evening to early overnight period as convection moves through.
Deterministic guidance does suggest corridors of 1+ inches of rain
are possible through the overnight period, mainly for areas in
central to north-central Wisconsin. Probabilistic guidance keeps
the probability of exceeding an inch at any one location to around
20-40%. Taken together this suggests potential for localized
heavy rainfall is high, but the exact locations of where the
highest amounts fall is less certain although central Wisconsin
will be the best bet. A final consideration will be how long rain
lasts into Saturday, which will add on to any rain totals from
Friday through Friday night. On the worst case side, rainfall
totals could push over two inches by end of day Saturday if rain
sticks around for a longer duration.

Next week...
Quieter conditions are then expected for the rest of the weekend
and early next week. Long range guidance doesn`t bring another
round of active weather through the area until around the middle
of the week, when the next cold front will cross the area.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 638 AM CDT Wed Jul 9 2025

A low stratus deck will impact most TAF sites this morning,
bringing IFR/LIFR ceilings and some patchy fog with visibility
reductions. Clearing behind the stratus is visible on satellite,
working its way down the Bay of Green Bay and into north-central
Wisconsin. Between these areas of clearing and warming
temperatures through the morning hours, expect low ceilings and
any fog to lift by the early afternoon. Included a TEMPO for the
transition period. Good flying conditions are then anticipated for
the rest of the day under VFR skies. Another round of potential
patchy fog is possible late tonight, but confidence wasn`t high
enough to include in the current TAF.

&&

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

&&

$$

DISCUSSION.....Uhlmann
AVIATION.......Uhlmann