609
FXUS63 KGRB 011130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Tue Sep 1 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Warm, humid conditions continue today with highs in the 80s to
  lower 90s. Heat indices climbing into the lower to middle 90s
  across central into northeast WI.

- Marginal Risk (Level 1 of 5) of severe storms late tonight into
  Wednesday south of a Merrill to Wausaukee line. The main risk
  would be strong or damaging winds and hail up to one inch in
  diameter.

- Above normal temperatures and the periodic chances of
  thunderstorms will continue Thursday into weekend.

&&

.DISCUSSION...
Issued at 215 AM CDT Tue Sep 1 2026

The first day of meteorological fall will be a warm one with highs
in the 80s to lower 90s. The heat index will climb into the lower
to middle 90s across central into northeast WI. Attention then
turns to late tonight when a warm front will lift northward
towards the area. A 40 knot 850mb low level jet/850mb warm
advection will trigger thunderstorm activity across Minnesota and
western WI during the evening, then overspread the area after
midnight. Mid-level lapse rates not all that impressive at 5.5
to 6 C/KM. However, low level winds at 850mb are expected to
increase to about 40 knots towards 12z at Green Bay. Wind shear
values of at least 30-40 knots and CAPE values of 500 to 1,500
J/KG would support the potential for strong/damaging wind gusts
and potential for hail up to one inch in diameter. After the
storms exit Wednesday morning, a lot of uncertainty if storms
would redevelop across east-central WI during the afternoon.
Only have a 20-30% chance into the evening.

For Thursday into the weekend, above normal temperatures are going
to continue with the periodic chances of thunderstorms. Hopefully
some of these storms will move across our area to help alleviate
the on-going drought. Placement of the axis of heavier rain will
be difficult to pinpoint this far out based on the upper air
pattern. Otherwise, late guidance is suggesting cooler
temperatures early next week, a hint of the changing of the
seasons.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 624 AM CDT Tue Sep 1 2026

Low clouds and fog were at or below airport minimums north
and west of Green Bay and Appleton. The only exception was
at KAUW/KCWA where conditions improved over the last hour.
The fog and low clouds should clear the area by 14-15z with
fair weather cumulus developing after 16z between 2,500 and 4,000
feet rising to 5,000 to 8,000 feet this afternoon. Light
and variable winds become south/southwest with gusts to around 20
knots this afternoon. Showers and thunderstorms should arrive
across central WI after 06z, and then towards the Lake Michigan
shoreline towards 12z Wednesdsay. Showers and storms should exit
the area Wednesday morning.

&&

.FIRE WEATHER...
Issued at 215 AM CDT Tue Sep 1 2026

Drier air is still expected to move into northern WI today.
Deep mixing, winds gusting to around 25 mph and warm temps may
lead to elevated fire weather conditions in north-central WI,
especially Vilas County this afternoon where RHs should dip into
the upper 20s and lower 30s during peak heating. Per coordination
call yesterday with surrounding offices and the DNR, no SPS will
be issued as just enough enough moisture from previous rains
should keep any fire danger subdued, especially with the latest
fire danger in the low category.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT this morning for WIZ005-
010>013-018>021-030-031-035>037-045-073-074.
&&

$$

DISCUSSION.....Eckberg
AVIATION.......Eckberg
FIRE WEATHER...Bersch/Eckberg

NWS GRB Office Area Forecast Discussion