206
FXUS63 KGRB 122348
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
648 PM CDT Sun Jul 12 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Intense heat is expected Monday and Tuesday with highs in the
  90s with a few locations around 100 degrees. Heat indices both
  days will range from 95 to 105 degrees, resulting in heat
  related impacts. A Heat Advisory has been issued for the entire
  area from 11 AM Monday to 9 PM Tuesday.

- Showers and storms are possible at times from Thursday through
  next weekend. It is too early to determine their severity.

&&

.DISCUSSION...
Issued at 328 PM CDT Sun Jul 12 2026

Precipitation/Thunder Chances...This afternoon`s satellite imagery
showed the anvils of a cluster of showers and storms moving over the
central U.P. while mostly sunny skies prevailed across the forecast
area. Pairing along with this, radar imagery showed the cluster/line
of showers and storms tracking south/southeast over the central
U.P.. This leads to the bigger question of if these showers and
storms will track south enough to reach far northeast WI and Door
County late this afternoon into this evening. Despite the CAMs
struggling with this feature all day, anticipate the tail of this
cluster/line to clip far northeast WI or Door County late this
afternoon into this evening. If these storms can reach these
areas/hold together, 1500-2500 J/kg of CAPE and 0-6km shear of 30-35
kts would support the potential for strong or severe storms capable
of damaging winds. Otherwise, they may pass just to the east of the
area or dissipate before reaching the area.

Dry conditions are then expected for Monday through at least
Wednesday with a strong upper-level ridge prevailing over the area.
Wednesday into Thursday, the upper-level pattern transitions to a
northwest flow, leaving the forecast area in the line of fire for
any shortwaves riding the ridge. This brings the next chances for
showers and storms to the area from Thursday through the end of next
week. But, it is too early to determine timing or the potential for
severe weather and heavy rainfall.

Dangerous Heat/Temperatures...As the upper-level ridge prevails
overhead early this week, hot air will accompany it, peaking Monday
and Tuesday. 925mb temps will climb to 26C to 34C over the area each
afternoon with 850mb temps of 23C to 26C. This will lead to air
temps in the 90s to some spots approaching or reaching 100F. The
bigger question is how well or if the area/parts of the area will be
able to mix to 850mb to tap into those 850mb temps. If we can mix,
the air temperature will increase, but dew points (and therefore
heat indices) will decrease. For now, the higher dew points, in the
upper 60s to low 70s, are progged across central and east-central
WI, with low to mid 60s across the Northwoods. This brings heat
indices in the 95 to 105 degree range across the area for Monday and
Tuesday, with the highest values in far northeast WI and Door
County. Decided to issue a Heat Advisory from Monday morning through
Tuesday evening, since overnight heat indices will still be around
75 degrees, leaving little recovery time to shelter from the
afternoon heat. Given some locations have heat index values around
105 or a couple of degrees above, debated on issuing an Extreme Heat
Warning, but since these values would only occur for a short period
of a couple hours and were not widespread across the counties of
concern, decided to keep the headline as an advisory. If the
forecast changes and dew points look to increase, an upgrade to an
Extreme Heat Warning may be needed for some counties.

As the ridge breaks down to the northwest flow midweek, temperatures
will not be as hot as Monday and Tuesday, but will still remain
above normal in the 80s to low 90s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 646 PM CDT Sun Jul 12 2026

VFR through the period with just a few high clouds. Looks too
capped on Monday for even fair weather cu. Only issue is right
at the beginning of the TAF period this evening at GRB. Outflow
from earlier storms over northern Door County is shifting down the
bay. If this holds together, a brief wind shift to E-NE with
gusts over 15 kts could occur.

Otherwise, winds will settle back to less than 5 kts by late
evening for all sites, including GRB. West winds will gust over
15 kts at most of the TAF sites mid morning Monday through Monday
afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM Monday to 9 PM CDT Tuesday for WIZ005-
010>013-018>022-030-031-035>040-045-048>050-073-074.
&&

$$

DISCUSSION.....Kruk
AVIATION.......JLA

NWS GRB Office Area Forecast Discussion