342
FXUS63 KGRB 270143
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
843 PM CDT Sat Jul 26 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...



- 20-40% chance for thunderstorms late Sunday night into Monday,
  especially in central and north-central WI. Any storms could be
  strong to severe. Additional rounds of storms possible through
  midweek.

- Turning hot and humid again Sunday and Monday, with heat indices
  potentially over 100 degrees. Heat headlines may be needed one
  or both days.

- More seasonable and drier conditions return by mid next week, and
  are expected to continue to next weekend.

&&

.DISCUSSION...
Issued at 842 PM CDT Sat Jul 26 2025

Short Term...Tonight and Sunday

The pattern is more energetic this weekend as shortwave lows slide
throughout the western Great Lakes region.

Thunderstorm and Severe Potential: A shortwave continues to move
into Lower Michigan this evening. This has kicked up convection over
the Lower Midwest, which is fortunately staying well south of our
area; apart from the haze that continues to stream into the region,
satellite and webcams reveal hardly a cloud in the sky over
northeastern WI.

Our next chance for convection and potentially severe weather comes
Sunday evening over mainly central and north central Wisconsin as
some CAMs show a line of storms diving southeast from northern
Minnesota towards our area. While guidance shows plenty (3,000 J/kg
or more) of CAPE to work with in the EML (elevated mixed layer) as
well as robust lapse rates to support quick uplift, with hodographs
looking quite weak with little rotation to speak of, the only threat
that looks to be plausible are severe winds from outflow winds and
core collapse/downbursts; while not expected, a rogue spin-up
tornado or two cannot be completely ruled out given localized wind
convergence could potentially produce low-level rotation. However,
that`s if a) convection actually reaches north central and central
Wisconsin Sunday evening and b) if the convection can overcome the
modest CIN immediately above the boundary layer. Should these
conditions be met, then severe winds are on the table for our
western CWA Sunday evening (15%+ chance), with a rogue spin-up
tornado being possible as well (2% chance). As we continue into the
overnight hours Sunday, some CAMs show the convection dying out as
it moves into northeastern Wisconsin; in addition, CIN looks to
increase in the lower levels. Thus, expect shower and storm chances
to decrease with time Sunday night and for the severe weather
potential to drop next to zero by midnight local time.

Temperatures/Smoke: Smoke from upstream wildfires continues to lead
to hazy skies tonight, but guidance continues to favor a relief from
the near-surface smoke.

With warm advection moving overhead on Sunday, we could see even
warmer temperatures at the surface, with Heat Indexes getting into
the mid 90s to potentially flirting with 100F in some spots like the
Fox Valley and adjacent counties. However, it looks like some smoke
aloft moving in on Sunday will insulate the area a little. Thus,
while Heat Advisories could potentially still be issued for the Fox
Valley and surrounding counties given the ongoing EAA event and
unseasonable warm air, none has been issued yet as the trend for
Heat Index on Sunday as trended lower. Yet even if a Heat Advisory
isn`t issued for Sunday, folks should stay hydrated by drinking
water often and should take breaks in the shade or in air-
conditioned areas frequently if spending time outdoors.

Long Term...Sunday Night Through Saturday


After some shortwave impulses potentially move through early next
week, expect drier and more seasonable conditions for the latter
half of the week as high pressure builds from the Canadian Prairies
to the Great Lakes region by next weekend.

Showers and Thunderstorms: Shower and thunderstorm chances, while
low (20 to 30%), could linger Monday morning as the convection from
Sunday night potentially hangs around and possibly amplifies over
northeast Wisconsin by the afternoon hours as very warm temperatures
and dewpoints in the 70s support high CAPE once again. Given the
strong lapse rates and high potentially energy in the EML (elevated
mixed layer), we could see severe winds and potentially even a spin-
up tornado return over northeast Wisconsin Monday afternoon,
although an unimpressive hodograph looks to eliminate the threat for
severe hail.

Moving into Tuesday, it looks like another shortwave impulse is
projected to traverse through Wisconsin, bringing additional showers
and storms to the CWA; given the increased bulk shear and still-high
CAPE environment, some strong storms cannot be ruled out with this
round of convection.

Temperatures/Heat: Expect the warmest and most humid day of the
period to be on Monday as the warm air aloft becomes maximized and
south to westerly flow throughout most of the day brings moisture in
from the corn evapotranspiration. Would not be surprised if we see a
few spots get to a Heat Index of 100F on Monday afternoon, with the
best chances of this occurring over the Fox Valley and adjacent
counties (20% chance over Green Bay to 60% chance in Waushara County
according to the latest run of LREF). Thus, would not be surprised if
a Heat Advisory is issued/continued for the expected heat-related
concerns for Monday afternoon; again, limit your time outside and
avoid strenuous activities outdoors, especially during the peak
heating hours (10 AM to 4 PM) on Monday.

While temperatures are expected to be cooler on Tuesday via the
shortwave bringing convection over the area and the high pressure
over the Canadian Prairies building into the western Great Lakes,
high temperatures are still projected to get into the 80s with
dewpoints in the 60s to potentially even around 70F still in the
southern CWA, making the area feel quite humid and warm still.

Next Wednesday and beyond: Rain chances essentially go to zero by
next Wednesday as the high pressure moving through the Canadian
Prairies shifts towards the Great Lakes region, with the center
projected to eventually move over the Great Lakes by next weekend.
As this occurs, cooler and drier air from far northern Canada is
expected to advect into the Upper Midwest, bringing much more
seasonable if not slightly below normal temperatures back to our
area; expect highs to return to the 70s by the middle of next week
to next weekend.

&&

.AVIATION.../00Z TAFS THROUGH 00Z MONDAY/...
Issued at 620 PM CDT Sat Jul 26 2025

Generally VFR conditions are expected through the TAF period
with light winds overnight becoming southerly at 5-10 kts
through the day on Sunday. Otherwise, there is some potential
for patchy fog to form for a few hours around sunrise. Trended
towards a window for at least MVFR/VFR visibility reductions,
although IFR visibilities could occur in spots.

.OSH...Main aviation concern over the coming 24 hour will be the
potential for a window of fog around sunrise on Sunday. Chances
are at least low to medium (30-50%) for MVFR visibility with a
smaller (20-30%) chance for IFR visibility. Any fog should erode
by 13-14Z.

&&

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

&&

$$

DISCUSSION..... TAP/LC
AVIATION.......JM