991
FXUS63 KGRB 240407
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1107 PM CDT Mon Jun 23 2025

...Updated for 06z Aviation Discussion...

.KEY MESSAGES...

- The intense heat will come to an end from west to east this
  afternoon and this evening as a cold front, along with showers
  and thunderstorms spreads eastward across the area. The heat
  index will climb to around 100 degrees over northeast Wisconsin
  before the rain arrives.

- Strong or severe storms will cross the area through the evening,
  with damaging winds and torrential rainfall the primary hazards.
  Localized flooding is possible.

- Periodic chances of showers and thunderstorms will continue
  Tuesday through Friday morning. It is too early to determine if
  or when any of the storms would become severe.

- Locally heavy rainfall is possible at times on Wednesday and
  Thursday. Probability of receiving over 2 inches is 20- 40% over
  central WI.

&&

.DISCUSSION...
Issued at 222 PM CDT Mon Jun 23 2025

Main forecast concerns will be the end of the heat and the arrival
of a more active pattern, including the potential for severe
weather today.

Heat...
Southwesterly flow will continue to be in the area today, with
ample heat ahead of the cold front and its associated storms.
Current temperatures hold in the upper 80s to lower 90s in the
sunny areas, along with dewpoints in the lower 70s, which do
continue to support heat indices in the upper 90s to lower 100s.
Relief from the heat will arrive from west to east as rain moves
through and the synoptic cold front brings in some cooler air.

Storms Today & Tuesday... As of this discussion`s writing, some
convection is already under way ahead of the synoptic cold front,
with storms crossing into central Wisconsin. MLCAPE values in the
region ahead of this line are in the 1200-1600 J/kg range, which
should continue to support the development of this storm line
upstream. Strength and coverage are likely to grow also as the
cold front catches up and moves through during the late afternoon
and evening. Shear values from 0-6 km show around 30 knots,
predominantly in the mid to upper levels. These values could help
bring a modest amount of organization to the stronger storms, but
better shear continues to lag well behind the cold front. DCAPE
values and heavy precipitation loading on the other hand will
serve to make damaging wind gusts the main severe threat for
storms. If storms train over the same region or move more slowly,
there may be a marginal hydro threat as well, as any storms will
have the potential to produce heavy rain. Freezing level heights
and the general warmth of the entire airmass on the other hand
will severely hamper any hail growth in the region.

Once the storms push through the region by tonight, the main
front will sag south of the region, which will bring dry
conditions back to the northwoods but could keep a few showers in
central to east-central Wisconsin. Meso models largely don`t bring
much of the front northwards again until later in the day Tuesday,
so reduced pops through the overnight period before ramping back
up into Wednesday morning.

Storms the Rest of the Week...
With the stationary front in the region, active weather will
continue to flow through the Great Lakes region. A better
shortwave approaches for Wednesday which includes the evening and
overnight period, which could bring another round of better
organized and long lived active weather. This will again bring
some heavy rain potential to the region for the late afternoon and
overnight period, and will serve a better flooding concern than
today as storms will have better potential to train over the area.
As result we are in the Slight Risk category for excessive
rainfall. Fortunately, the main front itself will remain south of
the area, which will largely limit the potential for severe
weather, with the majority of the instability staying south of the
region. A brief break may be possible before the next shortwave
arrives from the west which may sustain active weather through
Thursday into Friday morning. If both day see heavy rainfall, for
which there certainly is some potential, area rivers may also see
rises and impacts in the following days.

Finally, some hints of a break or drier weather are possible as we
get into the end of the work week and into the early weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1106 PM CDT Mon Jun 23 2025

Challenging aviation forecast. A large swath of light rain with
sparsely embedded thunder is setting up to impact all sites
except for KRHI. KAWU and CWA on northern edge... expecting no
thunder at those sites.

All sites except for KRHI are slated to drop to MVFR. Held off
on any IFR for now, as confidence is not high enough. Will
monitor for fog potential overnight at all sites not KRHI. IF
fog develops, expecting vsbys of 4 to 6 miles at this time.


&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...None.
MARINE...None.

&&

$$

DISCUSSION...
AVIATION...Kotenberg
MARINE...