778
FXUS63 KGRB 280632
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
132 AM CDT Sun Jun 28 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- High heat and humidity will result in heat-related impacts for
  much of the upcoming week. Most oppressive conditions expected
  Monday and Tuesday.

- An Extreme Heat Watch is in effect Monday afternoon and evening
  for central Wisconsin and the Fox Valley.

- Mainly dry today with a small chance of thunderstorms (20-30%)
  over north-central Wisconsin this afternoon.

- Strong to severe storms possible tonight and again on Monday
  night. Main hazards would be damaging winds, large hail, and
  heavy rain.

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

&&

.DISCUSSION...
Issued at 132 AM CDT Sun Jun 28 2026

Severe Weather Potential Tonight:

Near normal temperatures are expected today north of an
approaching warm front with clouds increasing as a low pressure
system develops across the Plains. Highs today are expected to
range from the upper 70s to middle 80s, probably representing the
coolest readings for the upcoming week barring a day with an
overcast sky due to a dying MCS. An approaching warm front and
increasing low level jet (20-25 kts) could bring the chance
(15-25%) for showers and thunderstorms this afternoon, mainly
across north-central Wisconsin.

There will be a better chance (60-90%) for storms tonight across
the entire region as the surface warm front lifts north and the
low level jet strengthens further (35-50 kts). A surge of
instability (MUCAPEs of 3000-4000 J/kg) and effective shear of
30-40 kts will mean strong to severe storms will be possible.
Despite high wet-bulb zero heights of 10-12k ft there is a lot of
CAPE in the hail growth zone, putting large hail on the table
along with damaging winds. PWATs approaching 2 inches and abundant
moisture will mean heavy rainfall will also be likely.

Heat arrives Monday and continues through the week:

The warm front will surge north on Monday, meaning the heat is on
for much of the upcoming week. Starting Monday and for the rest of
the upcoming week, high temperatures of 90 or higher are expected
to be ubiquitous across the region. Although we are well into
summer, and on the precipice of July, the region hasn`t hit 90
degrees since late May. Therefore, this upcoming stretch of hot
weather may feel unusually oppressive, especially for sensitive
groups.

The hottest temperatures are expected to be Monday, where highs
in the lower to middle 90s will combine with dew points in the
lower to middle 70s, to produce heat indices from the upper 90s
to the lower 100s. Similar conditions are also expected on Tuesday
as the region remains well into the warm air. The main concern
these days is the presence of possible convection and lingering
convective debris clouds. This would act to limit high
temperatures and keep the area from reaching the triple digit heat
indices. At this point it appears central and east-central
Wisconsin will likely hit Heat Advisory criteria, with Extreme
Heat Warning criteria possible Monday and Tuesday.

HREF probabilities of hitting Extreme Heat Warning criteria are
50-70% across central Wisconsin and the Fox Valley Monday
afternoon into early Monday evening. Therefore, will issue an
Extreme Heat Watch as confidence isn`t high enough to go with an
Extreme Heat Warning with this forecast issuance.

Later in the week high temperatures remain in the upper 80s to
lower 90s as dew points fall into the upper 60s to lower 70s. This
will keep heat indices in the middle to upper 90s across central
and east-central Wisconsin, with values hitting 100 degrees at
times. That being said, there is expected to be storms at times
throughout the week so the oppressive heat will likely not be
every single day as one of the days will likely have convective
debris or showers and thunderstorms, which will keep highs well
below 90. Picking which day this will occur is problematic as
model solutions are not in agreement on timing.

Severe Weather Potential For the Week:

The hot weather and moisture will provide ideal conditions for
showers and thunderstorms through much of the upcoming week. The
key will be when this occurs and how much instability is around
when the storms develop. Right now there is a decent signal for
storms Monday night into Tuesday morning and again Tuesday night
into Wednesday morning. However, as was noted previously there
isn`t much in the way of model consensus and depending on the
strength and placement of the upper level ridge, these ridge
riders could just as easily go around the area and leave us mostly
dry. Any storms that do make it into the area would be strong to
severe given the instability and shear in place, as evidenced by
SPC outlooks. The most likely element from any storms would be
heavy rainfall given the high PWATs and long CAPE profiles. Any
areas that get repeated activity would also be under consideration
for flooding from saturated soil. Right now it appears the best
chance for strong to severe storms is across northern Wisconsin
Monday night into Tuesday morning on the periphery of the upper
level ridge with things getting murkier beyond this point in the
forecast.

The ridge begins to retreat towards the middle to late part of the
week, which would allow better chances for showers and
thunderstorms across the region and raise the chances for repeated
heavy rainfall. This also increases the chances for high
temperatures to under perform given the increased risk of
convective debris lingering across the region. Any thunderstorms
during the middle to late part of the week would also carry the
risk for severe weather given the instability and shear in place
near a frontal boundary expected to linger across the western
Great Lakes.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1205 AM CDT Sun Jun 28 2026

VFR conditions are expected through the TAF period. High clouds
will stream in during the overnight period. Clouds will then
thicken and lower throughout the day on Sunday as a low pressure
system develops across the Plains. There will be chance (15-25%)
for showers and thunderstorms across central and north-central
Wisconsin during the afternoon; however, the probability is too lo
to include at the TAF sites. There is a better chance (30-50%)
Sunday night as showers and thunderstorms develop north of an
advancing warm front. Some of these storms could be strong to
severe. Given the better chance, will include a PROB30 across the
central and north-central Wisconsin TAF sites Sunday evening.

Winds will generally be light from the east-southeast overnight.
Winds will then become southeast Sunday and increase to 10 to 20
knots by the afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Watch from Monday afternoon through Monday evening
for WIZ030-031-035>039-045-048-049.
&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kurimski

NWS GRB Office Area Forecast Discussion