177
FXUS63 KGRB 101123
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
623 AM CDT Fri Jul 10 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Isolated thunderstorms are possible during the afternoon and
  early evening hours across the north today and Saturday. Main
  hazard would be brief heavy rain, lightning and wind gusts to
  around 30 mph in the stronger storms.

- Patchy to areas of ground fog continue through an hour or two
  after sunrise this morning, and are forecast to develop again
  late tonight. The fog may result in localized reduced
  visibilities for motorists.

- Building heat and humidity early next week will bring a period
  of minor heat-related impacts, with heat index values forecast
  to rise into the middle to upper 90s on Monday and Tuesday.

&&

.DISCUSSION...
Issued at 200 AM CDT Fri Jul 10 2026

Skies were mostly clear across much of the region early this
morning. Areas of fog were noted with temperatures ranging from
the middle 50s to lower 60s north to the middle to upper 60s
south. The fog should linger through sunrise, then dissipate a
few hours later. The latest change to the forecast is to add
isolated thunderstorms to the forecast during the afternoon and
early evening hours today and Saturday across the north.

Several meso-models, a few of the global models, along with the
HREF paintball members supported isolated convection (20-25%
chance) during the afternoon into the early evening today and
again on Saturday. This was supported that SPC Day 1 and Day 2
Outlooks that portions of the area were in general thunder. Bufkit
soundings at Rhinelander indicated 500 to 1,000 J/KG of CAPE and
shear values around 25 knots. The parameters were similar for
Saturday. The main hazard with any storm would be brief heavy
rain, lightning, and wind gusts to around 30 mph. We are at the
height of the boating and camping season, so any isolated storm
may be impactful.

For Sunday, there is a 20 percent chance of thunderstorms across
far northeast WI. The 500mb ridge builds early next week, with
700mb temperatures warming to 12-14C resulting in the area being
capped. 850mb temps warm to 20-22C supporting high temperatures
in the lower to middle 90s. The 12z ECMWF and 00z MEX guidance
numbers for highs on Monday and Tuesday were very similar. NBM
dewpoints were on the low side compared to the numerical guidance
values. This is important as a degree or two difference in the
dewpoint temperatures can have a big impact on the maximum heat
index. Current heat index values are forecast to be in the middle
to upper 90s, however if the higher dewpoints are reached could
result in possibly a Heat Advisory for portions of the area. Heat
related impacts are likely to be felt during the first half of
next week.

On Tuesday night and Wednesday, a weak frontal boundary will drop
southward into northern WI. This may be the focus for thunderstorm
activity Wednesday afternoon into Wednesday night. Depending on
where convection sets may have a significant impact on convective
trends on Thursday.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 618 AM CDT Fri Jul 10 2026

Patchy ground fog should dissipate by 9 am this morning.
Otherwise, fair weather cumulus between 2 and 3 thousand feet this
morning will rise to 4,000-6,000 feet later this afternoon.
Isolated thunderstorms (20-25% chance) are possible this
afternoon across the north. Coverage is so low, decided not to
add to the KRHI 12z TAF. The storms and cumulus field will
disappear after sunset this evening followed with more patchy fog
late Friday night. Isolated storms are possible again Saturday.

&&

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

&&

$$

DISCUSSION.....Eckberg
AVIATION.......Eckberg

NWS GRB Office Area Forecast Discussion