690
FXUS63 KGRB 131110
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
610 AM CDT Mon Jul 13 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

-Scattered showers and isolated thunderstorms will move across far
 eastern WI early this morning, ending by sunrise.

- Intense heat is expected today 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 night
  through next weekend. It is too early to determine their
  severity.

&&

.DISCUSSION...
Issued at 225 AM CDT Mon Jul 13 2026

The complexities of summer forecasting. A complex of thunderstorms
across eastern Upper Michigan was moving into northern lower
Michigan. Special Marine Warnings are in effect on the other side
of the lake. About an hour ago, it looked like the showers and
storms would clip far northern Door County. Since then, scattered
showers and maybe a thunderstorms have developed westward across
Menominee and Dickinson counties in Upper Michigan. Based on radar
trends, have expanded and extended rain chances (isolated storms
possible) west into Marinette and all of Door into Kewaunee county
for a few hours early this morning. The rain should be out of
here by sunrise.

For the heat, with the expected hot temperatures forecast today
and tomorrow, a few degrees difference in the dewpoint can make
the difference between a Heat Advisory compared to a Heat
Warning. Looking at what happened yesterday, thinking the lower
dewpoints is the way to go. Bufkit soundings indicated a lot of
dry air off the surface, even drier on Tuesday that will mix out
the dewpoints. Also, noticed the last few days Green Bay has not
warmed to the expected values on the MET/MAV guidance despite
925mb temperatures supporting the warmer temps. Based on the
latest 925mb temps, have nudged down high temperatures a degree
or two over central and east-central WI. Tuesday will be or maybe
a tad bit hotter than today for some locations. For later tonight,
heat index values are likely to drop below 75F for a few hours.
The break is not long enough to worry about criteria in this case.
A second day of hot temps will help accumulate heat related
impacts across the region. Will have a weather story/social media
post with heat related strategies to protect yourself from the
heat. Based on calculated temp/dewpoints, current Heat Advisory
look to be in good shape.

A cool down, well relatively speaking, on Wednesday and Thursday
with highs a few degrees either side of 90. Heat indices should
climb into the upper 80s to middle 90s. For Thursday night
through next weekend, ridge will begin to break down as
temperatures return to closer to normal. There are periodic
chances of thunderstorms during this time frame, however there
is low confidence on when/where storms would occur.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 605 AM CDT Mon Jul 13 2026

VFR conditions prevail through Tuesday. West to southwest winds
around 10 knots will gust from 14 to 19 knots this afternoon.
After sunset, winds will be around 5 knots. Similar wind speeds
and gusts are also possible on Tuesday.

&&

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

$$

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

NWS GRB Office Area Forecast Discussion