427
FXUS63 KGRB 171108
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
608 AM CDT Thu Jul 17 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Cooler and less humid conditions expected today and Friday.

- A Small Craft Advisory is in effect for the bay and nearshore
  areas of Lake Michigan this morning.

- An active pattern is expected Friday night through the middle of
  next week with periodic chances of rain and thunderstorms.
  Stronger storms and heavy rain are possible at times.

&&

.DISCUSSION...
Issued at 339 AM CDT Thu Jul 17 2025

Short Term...Today...Tonight...and Friday

Showers will wind down this morning as a low pressure system
continues to move east as a high pressure system settles in across
the western Great Lakes region. The high will bring much cooler
temperatures to the area today, as highs only range from around 70
across the north to the lower 70s across the rest of the region.

The high will drift east over the central Great Lakes tonight,
but still maintain its influence across the area. Light winds and
mostly clear skies will allow temperatures to fall into the upper
40s across the north tonight, with lows in the lower 50s across
central and east-central Wisconsin and upper 50s along the
lakeshore.

The high will continue to drift east on Friday, which will allow
surface winds to turn to a southerly direction and daytime highs
to inch upward a few degrees. A shortwave tracking across the
northern Great Lakes will bring a small chance (20-30 percent) for
showers across portions of north-central Wisconsin Friday
afternoon. Highs on Friday are expected to range from around 70
across the north to the middle 70s across central and east-central
Wisconsin.

Long Term...Friday Night Through Wednesday

Rain and thunderstorm chances return Friday evening and Saturday
as a system approaches from the west. However, exact timing and
location details remains challenging to pin down as models vary
on the strength and location of associated features. With a
surface warm front to the south, some LL warm advection, and a
weak LL jet pointing towards the area late Friday, this could aid
in developing a rain/storm complex Friday night into Saturday
morning somewhere in the vicinity; however, not all models are in
agreement on this. Additional rain chances occur throughout the
rest of Saturday with broad lift from the RRQ of an upper jet, a
weak mid- level shortwave to the north, and a ill-defined surface
low moving across the state. PoPs are generally in the 40-70%
range from Friday evening through Saturday afternoon, but do not
expect all hours to be rainy. Severe weather potential is also
tough to determine for the same reasons, but other than the often
overdone NAM, CAPE maxes out around 1000 J/kg Saturday afternoon.
Shear is higher across northern WI, but this is offset from the
better CAPE, and lapse rates are modest. Therefore, while an
isolated severe threat cannot be ruled out, the potential for any
widespread severe storms appears low. NBM and LREF probabilities
only show a 10% chance for 1.0" or more of rain throughout this
time period, but if a more substantial complex develops late
Friday some localized heavy rain could be possible, mainly across
the southern forecast area where pwats up to ~1.7" are noted and
where precip is more likely in general due to proximity to the
warm front.

After Saturday, there is agreement that high pressure will result
in dry conditions on Sunday.

An active weather pattern sets up next week as slow moving and
waffling frontal boundaries stall out over or around the area,
along with various shortwaves and an active LL jet. This will lead
to on/off chances for rain and thunderstorms, with the potential
for heavy rains and/or stronger storms in the mix. But determining
the specifics will be difficult other than 1-2 days out due to
the dynamic nature of the setup and each day will impact the next.

Temperatures will be at or just below normal Saturday and Sunday,
and then trend warmer through the rest of the week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 542 AM CDT Thu Jul 17 2025

IFR/MVFR ceilings and isolated showers and sprinkles will
dissipate this morning as high pressure brings drier air across
the region. Flying conditions are expected to improve to VFR
everywhere later this morning and remain there for the rest of the
TAF period. Some afternoon cumulus clouds are expected later this
morning and afternoon with the heating of the day, with mostly
clear skies expected tonight. Gusty northerly winds to 15 to 20
knots will ease later this afternoon below 10 knots and continue
through tonight.

&&

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

&&

$$

DISCUSSION.....Kurimski/KLJ
AVIATION.......Kurimski