NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 281929
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
229 PM CDT Sun Jun 28 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Small chance of thunderstorms (20-30%) over central and 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.

- 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 Warning is in effect Monday afternoon and
  evening for central Wisconsin and the Fox Valley. An Heat
  Advisory is in effect for the rest of northern and northeastern
  Wisconsin.

&&

.DISCUSSION...
Issued at 228 PM CDT Sun Jun 28 2026

Severe Weather Potential Today and Tonight...

A decaying MCS will bring a brief chance of rain to the area along
with widespread high cloud cover, but is expected to have minimal
impact during the afternoon. Assosciated precipitation will have
around a 20-30% chance of reaching the surface.

The main focus of the active weather today will be for storms
tonight (60-90% chance) as a surface warm front lifts into the
region. Keeping with previous forecasts, the LLJ now ramps up a
couple hours sooner, with short-term guidance suggesting initation
as early as a couple hours before midnight across western and
central Wisconsin before expanding storms eastwards into the rest
of the area. The warm front will bring a surge of instability and
ample moisture, providing the means for organized convection and
strong to severe storms overnight. Damaging winds and very heavy
rainfall will be possible with any storms. Abundant PWATs pushing
upwards of 2 inches do suggest that some areas may see very
localized rainfall amounts over an inch under the stronger storms.
This will likely not be widespread by may need watching if storms
train over an area. The area is in the Marginal Risk (5% chance)
of excessive rainfall. As for hail, models have increased the
available instability aloft through the hail growth zone over the
last 24 hours, which would support getting hail to the surface
despite the deeper warm layer. Finally, the earlier start time has
also moved up the departure time of precipitation Monday morning,
with drier conditions spreading across the area by the mid-morning
hours as capping establishes itself aloft behind the warm front.

Storms Monday Night and Tuesday Night...

Ample moisture and heat will provide the instability for storm
development through the upcominn work week. However, lingering
warm air aloft will limit surface based storms at times. Thus, the
placement of the upper ridge and assosciated 'heat dome' over
eastern CONUS will remain the critical components to watch for
convective potential for our area. The first shortwave will cross
the Upper Midwest Monday night into Tuesday, but will largely
inititate in Minnesota. This system will then spread eastwards
through the evening, but capping over our area should help weaken
storms as they arrive. This will limit the best severe potential
to our west, with the Marginal Risk currently limited to portions
of central to north- central Wisconsin. This scenario then repeats
Tuesday evening as the next shortwave arrives, but this time the
ridge will be slightly more east, possibly bringing the storms
more into our area. That said, the details of convection each day
are muddy, largely depending on when/where storms developed the
previous day. That said, the upper ridge is expected to continuing
shifting eastwards through the work week, bringing us into the
line of fire of any shortwaves along the upper ridge. Any storms
Monday and Tuesday will have the potential to be strong to severe
given the instability and moisture around. The most likely hazard
will be very heavy rainfall, especially if storms repeat each day
and soils become heavily saturated.

Dangerous Heat...

Active weather aside, the heat accompanying the upper ridge will
be a hazard itself. Dewpoints well into the 70s accompanied by
high temperatures into the 90s will bring heat indices well into
the upper 90s to mid-100s Monday and Tuesday. With the strong heat
signal over central Wisconsin and probabilistic guidance still
suggesting around 60-80% chance of exceeding 104 heat indices,
decided to convert the Extreme Heat Watch into an Extreme Heat
Warning for all of central to east-central Wisconsin. The most
likely areas to get the extreme heat will be central Wisconsin
into the Fox Valley, but also included the lakeshore areas for the
inland portions of the counties. Those living along the shoreline
of Lake Michigan and north of Sturgeon Bay should see
significantly lower impacts than those further inland. North of
the Extreme Heat Warning, heat indices will remain just below
advisory criteria during the afternoon, lingering in the 95-99
range. However, overnight temperatures are unlikely to drop below
75 in many areas, which typically means little relief from the
heat for those without shelter and means of cooling. Given that
this makes for a long stretch of heat, and also that the forecast
keeps overnight temperatures up even as high temperatures drop
slightly by Wednesday, decided to issue a Heat Advisory for the
rest of the region.

As we get into the mid to late week, heat indices should see a
minor drop, but temperatures are currently forecast to remain in
the upper 80s to lower 90s each day. The main complicating factor
for headlines during this period will be convective weather, as
any storms could provide some relief and lower the daytime high in
some areas. On the other hand, the forecast keeps heat indices for
most of the area above 70 through Friday, which would compound
heat fatigue effects for those without shelter as mentioned above.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 640 AM CDT Sun Jun 28 2026

VFR conditions remain in the region through much of the day today.
High clouds will move in over the afternoon as the remnants of a
rainy system approach central Wisconsin. Added a small period of
rainfall for the decaying system over Minnesota this morning, but
expect relatively low impacts to aviation when the showers
arrive. Of greater concern will be the potential of severe storms
late tonight as storms develop north of an advancing warm front.
Some of these storms could be strong to severe, but coverage of
thunder is a little less certain so kept thunder to a PROB30 group
for now during the overnight period. Some of the storms could be
strong to severe. Expect ceilings and visibility to decrease with
the storms arrival, bringing MVFR/IFR ceilings into the area.

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...
Heat Advisory from noon Monday to 7 PM CDT Tuesday for WIZ005-
010>013-018>021-073-074.

Beach Hazards Statement from late tonight through Monday evening
for WIZ022-040-050.

Extreme Heat Warning from noon Monday to 7 PM CDT Tuesday for
WIZ022-030-031-035>040-045-048>050.
&&

$$

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