NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 271850
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
150 PM CDT Sat Jun 27 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- High heat and humidity will result in heat-related impacts much
  of next week. Most oppressive conditions Monday and possibly
  Tuesday.

- Mainly dry this weekend with small chance of thunderstorms (20-
  40%) over central Wisconsin Sunday afternoon.

- Strong to severe storms possible Sunday night and again on
  Monday night, especially northern Wisconsin. Main hazards would
  be damaging winds along with heavy rain.

- Periodic chances for thunderstorms Tuesday through late this
  week. Some of these storms could become strong or severe.

&&

.DISCUSSION...
Issued at 150 PM CDT Sat Jun 27 2026

Today Through Sunday...
Pleasant and quiet conditions are expected for the region today, with
high temperatures in the upper 70s to lower 80s. These are also
the coolest high temperatures currently in the forecast.

Sunday the surface warm front will remain south of the region but
warm air advection will begin aloft. Expect increasing clouds
through the morning with quiet conditions into the early to mid
afternoon. The strongest corridor of theta e advection will linger
to our west and south through the afternoon and early evening, but
most recent guidance continues to suggest a couple isolated storms
may ride the gradient into our region by the late afternoon and
evening. This feature may be supported by a weak mid-level
shortwave and warm air advection aloft along with an increasing
LLJ. Therefore added pops around 20-40% into portions of central,
north-central, and east- central Wisconsin during the late
afternoon to evening period.

The better chance for storms remains in the late overnight hours.
The strengthening LLJ will serve to bring increased warm air
advection to the region and raise MUCAPEs to around 1000-2000J/kg.
The changes in the forecast for the afternoon will also impact
this time period, expanding the unstable air further eastwards
during the overnight period along the nose of the LLJ into
portions of central and north-central Wisconsin. SPC Day 2
expands the Marginal Risk of severe weather into portions of
central to north- central Wisconsin as a result. Damaging winds
and very heavy rainfall are the most likely severe weather
concerns. PWATs around 2 inches combined with wet bulb zero
heights up to 13-14 thousand feet will serve to bring localized
very heavy downpours within any convection. These same factors
will likely serve to limit hail however.

Oppressive Heat Arrives Monday into Tuesday...
All signs point to the potential for dangerous heat Monday behind
the warm front that will push through during the day. Surface
dewpoints during this time will surge into the 70s, with
probabilistic guidance suggesting around 90%+ of exceeding a 70
degree dewpoint and a corridor 40-60% of getting dewpoints up to
75 degrees. These dewpoints will feel very muggy and tropical.
Aloft, 850mb temperatures to around 22-24 C will support surface
temperatures into the lower to middle 90s. Combined, heat indices
pushing over 100 will be likely, with potential to exceed 105. The
only limiting factor may still be small discrepancies in timing,
with the aforementioned 850mb temps arriving later in the day on
Monday, rather than peak heating. Probabilistic guidance has
around 15-20% chance of exceeding 105 across small portions of
central to east-central Wisconsin at this time. Therefore, held
off on heat headlines for the moment.

Tuesday will also still be under the same airmass and does show
some signs of having the greater potential to bring heat indices
to the 100-105+. This time the main limiting factor may be active
weather, as Monday night convection may still be in the region and
additional development will be possible later in the day (see the
thunderstorm section below for more).

From here, the upper ridge does show some progression eastwards by
the middle of the week, putting our area on the edge of the heat
dome. This should be enough to drop both dewpoints and high temps
a couple of degrees. This will unfortunately still mean little to
no relief to the heat however, as heat indices remain in the
middle to upper 90s and the compounding heat over multiple days
will increase the overall heat exhaustion danger, especially as
overnight heat indices are not expected to drop below 74 until
Friday night.

Storm Potential Through the Week...
The ample heat and moisture will also serve to provide the
ingredients for active weather for the upcoming work week. Monday
may see active weather still suppressed during the day as the same
22-24 C temps at 850 that brought the heat to the surface will
serve to cap convection. Still, an approaching shortwave to our
northwest does show early signs of developing convection upstream
Monday night, which may ride the gradient of better instability
into our region Monday night. While capping will likely erode
storm strength as it gets into the area overnight, the remaining
clouds and rain may stick around long enough into Tuesday to
hamper the temperature forecast or leave some boundaries behind
which may organize additional convection later in the day. Any
severe storms during this timeframe will like see damaging winds
and heavy rainfall as the main risks. Finally, as the upper ridge
shifts eastwards by the middle of the week, capping will become
weaker for our region and additional rounds of convection will be
possible Wednesday and Thursday. Timing of any convection is
uncertain this far out, as each round of active weather will
impact the development of the next. Repeated storms will however
bring a risk of heavy rainfall given the lingering warm and moist
airmass.

Finally, late this week, mid-level ridging reorients shifting
from the eastern Ohio valley more toward the Mississippi River
valley into the western Great Lakes, taking our region out of the
true ring of fire. We'll have to see how this carries forward into
the 4th of July holiday weekend. That is just tough to say this
far out.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1239 PM CDT Sat Jun 27 2026

VFR conditions are expected through the TAF period. Fair weather
cumulus this afternoon will range from 4000-5000' AGL but should
have minimal impact on the ground operations. Winds will generally
be light from the east-southeast but a few gusts are possible up
to 15 knots at times.

The next chance of storms will not be until late Sunday afternoon
and Sunday night.

&&

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

&&

$$

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