NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 291815
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
115 PM CDT Mon Jun 29 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- An Extreme Heat Warning is in effect from this afternoon through
  Tuesday for central Wisconsin and the Fox Valley. A Heat
  Advisory is in effect for the rest of northern and northeastern
  Wisconsin for the same time period.

- High heat and humidity will result in continued heat-related
  impacts for the middle to late part of the week.

- Gusty onshore southerly winds will result in high waves and
  dangerous currents on Lake Michigan beaches through Tuesday
  evening.

- Periodic chances for thunderstorms expected at times this week.
  Some of these storms could become strong or severe. Main hazards
  would be damaging winds, large hail, and heavy rain.

&&

.DISCUSSION...
Issued at 115 PM CDT Mon Jun 29 2026

Storms Potential the Next Couple of Days...
Ample moisture and heat will provide the instability for storm
development through the upcoming week. However, lingering warm air
aloft will limit surface based storms at times. Thus, the
placement of the upper ridge and associated '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 tonight into Tuesday, but will largely initiate
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.

Tuesday the ample heat and moisture in the region during the
afternoon will provide for significant instability at the surface
under relatively weaker capping than today. Timing of convective
initiation remains tricky, but generally suggest development
along a weak surface boundary before following the instability
into our area. Shear around 40-50 knots will serve to organize
storms and will likely lead to more progressive systems that move
relatively quickly across the area. Therefore would expect
damaging winds and heavy rainfall to the be primary severe weather
concerns for the region. Additional convection is then possible
again overnight as another guidance brings another weak shortwave
and accompanying warm air advection into the region late overnight
into Wednesday. If we get two rounds in the same areas, may need
to watch for any lingering boundaries and intensification.

Wednesday...
Active weather potential continues into Wednesday as get closer to
the edge of the 'heat dome' to our east. A surface boundary
stretching over the Upper Midwest through northern Wisconsin on
Wednesday, which may serve to sustain any ongoing overnight
convection mentioned above or to help redevelop additional storms
during the afternoon and evening period later in the day. Storm
timing/location will heavily depend upon the details of
convection the previous 48 hours; but strength potential-wise
there will be ample heat and instability to work with to produce
some stronger storms during the afternoon and evening.

Dangerous Heat...

Dangerous heat works its way into the region this afternoon.
Dewpoints have already pushed well into the 70s across the region,
making the outdoors feel very muggy if not tropical. As cloud
cover scatters out expected temperatures to make a push towards
the 90s across central to east-central Wisconsin, pushing heat
indices into the upper 90s to lower to mid 100s. Only northern
Wisconsin may see temperatures a few degrees cooler, as the robust
low clouds cling on for a few more hours and lower daytime highs a
couple of degrees. Still, probabilistic guidance remains in good
agreement on heat indices over 104 today and again on Tuesday, so
will continue the Extreme heat Warning. well into the 70s
accompanied by high temperatures into the 90s will bring heat
indices well into the upper 90s to mid-100s today and Tuesday.
With the strong heat signal over central Wisconsin and
probabilistic guidance still suggesting around 60-80% chance of
exceeding 104 heat indices, will keep the current headlines of 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. There
remains a a signal on Tuesday that southern Oconto and southern
Marinette counties may reach Extreme Heat Warning criteria Tuesday
afternoon; however, will continue hold off on any upgrades for
these areas since overnight convection or clouds could impact
temperatures on Tuesday.

Those living along the shoreline of Lake Michigan and north of
Sturgeon Bay should see significantly lower heat related impacts
than those further inland. North of the Extreme Heat Warning,
heat indices are expected to hit the 95-99 range, which would be
just below typical heat criteria. 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, the Heat
Advisory remains in the forecast.

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 while heat indices remain in
the 90s. 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. Depending on how these
convective trends and clouds play out, an extension of heat
headlines is not out of the question.

4th of July Weekend...

Looking ahead to the 4th of July weekend, current trends suggest
the heat will linger in the region on Friday before pushing
southwards over the weekend. This will come with a downside, as
there will be lingering chances for showers and thunderstorms at
times as the front becomes the focus for convection as several
shortwaves track along the zonal flow across the western Great
Lakes region. At this time the best window for convection appears
to be Friday afternoon and Friday night as well as Saturday
afternoon into Saturday night, relying heavily on peak heating for
instability. With how far out this forecast still is, changes in
the timing are certainly possible. Storm strength also remains
difficult to assess this early, but given the ample expect
moisture and instability, strong to severe storms are certainly a
possibility for the weekend.

Temperature-wise we are expected to cool slightly into the 80s
Saturday and Sunday but heat index values on Friday will still be
well into the 90s, with values possibly approaching 100, cooling
into the lower 90s by Saturday and Sunday. As mentioned for heat
above, compounding extended heat may still a compounding effect
for the region despite the 'cooler' temps, especially as people
are more prone to spend their extended time outdoors for the
holiday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1220 PM CDT Mon Jun 29 2026

Low clouds continue to lingering the region this afternoon,
providing IFR to MVFR ceilings for much of the area. As
temperatures continue to rise through the afternoon, ceilings
should continue to lift, especially for central to east-central
Wisconsin, which should see the greatest improvement in flying
conditions. Tonight, some low cloud cover or fog may return as
temperatures drop again across the region. This may limit
visibility at times in many areas.

Winds will be out of the south this afternoon and tonight with
gusts up to 15 to 20 knots during the afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Tuesday for WIZ005-010>013-018>021-
073-074.

Beach Hazards Statement until 10 PM CDT this evening for WIZ022-
040-050.

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

$$

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