420
FXUS63 KGRB 241115
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
615 AM CDT Mon Aug 24 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Dry today, then shower/storm chances (40-80%) at times Tuesday
  afternoon through Wednesday evening. Low risk of severe weather,
  mainly Tuesday evening/night.

- Comfortable today with highs near normal, then temps climb
  slightly above normal with increasing humidity mid-week.

&&

.DISCUSSION...
Issued at 143 AM CDT Mon Aug 24 2026

Today into Tonight...Light winds, clear skies have produced ideal
radiational cooling conditions across the region early this
morning, with temps dropping into the 30s across the typical cold
spots across northern WI. A little patchy ground fog will once
again be possible early this morning and overnight into early
Tuesday, mainly across central and northern WI. Any fog would
burn off shortly after sunrise. Otherwise, dry and quiet
conditions are expected today into tonight, with high clouds
increasing through the day. It will be less windy, with northwest
winds generally under 12 mph, with some higher gusts this morning
in/near Door Co.

Shower/Storm Chances Tuesday into Wednesday...Chances for showers
and storms will increase on Tuesday as a shortwave and cold front
approach from the west. The HRRR is the most aggressive with the
first batch of showers and isolated storms, bringing it all the
way through the area Tuesday morning. Other CAMs hint at some
activity, but thinking the dry air will eat away at its eastward
advancement, so have only brought 20-30% chances in the parts of
central and north-central WI. Behind the initial area, instability
will build within the warm sector, with SBCAPEs climbing to at
least 500-1000 J/kg, highest in north-central WI, with some 2000
J/kg possible towards northwest WI. 0-6 km bulk shear should be in
the 25-30 kt range, allowing for some organized storm activity.
Could have some isolated activity in the warm sector during the
day, but the main show looks to develop across northwest WI during
the afternoon/evening as the shortwave dives into northern MN and
the front arrives. Machine Learning guidance has honed in on this
area for the greatest severe weather threat, which could extend
into parts of north central WI Tuesday evening (SPC brings the
Marginal Risk to the CWA border), with gusty winds and hail the
main threats. Storms will likely become more elevated through the
night, with the area of showers and embedded shores spreading
across the area Tuesday evening/night, with 50-80% chances across
the area. While widespread heavy rain is unlikely with probabilities
of over 0.5" at 50% or less (highest over northern WI), some
locally heavy rain will be possible in any storms, and especially
if any training storms occur. Other areas of moderate rain are
also expected Tuesday night into Wednesday morning, so many spots
will at least put a dent into the drought conditions. Models
remain in fair agreement with faster FROPA on Wednesday, pushing
the primary severe risk farther east. Enough cool air aloft with
the trough to result in shower/storm chances (20-70%, highest
north/east), especially during peak heating. Lingering instability
could lead to a strong storm with gusty winds and hail.

Thursday into the Weekend...northwest, cyclonic flow across the
western Great Lakes could produce a few showers on Thursday,
especially in the afternoon during peak heating and steepest low-
level lapse rates. But with the colder air aloft and better forcing
to our north/east, along with dry air, will limit the shower
potential with chances under 20% (highest near Door Co.). Dry
conditions are expected on Friday as weak high pressure slides
across the region. Next chances for showers and storms (20-40%)
move back into the area from the southwest this weekend as flow
aloft becomes more zonal. While the higher threat for severe weather
and flooding will be to our south/west, any northward shift would
bring the threat into our area, at least for a day or two.

Temperatures...After the chilly conditions this morning, temps
the rest of the week look to be near normal or slightly above
normal. Warmest days with highs in the low-mid 80s should be
Tuesday ahead of the front. Warmest night in the 60s much of the
area will be Tuesday night with clouds, showers/storms and some
wind. Lows could drop back into the upper 30s and 40s again late
this week over the north.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 615 AM CDT Mon Aug 24 2026

Other than very patchy ground fog, mainly across central and
north-central WI, early this morning and again late tonight, VFR
conditions are expected through the TAF period. Drier air will
limit the fair weather cumulus clouds today, but high clouds will
spread across the region through the day.

Winds will be lighter today, with northwest winds generally under
10 kts. Light and variable winds are expected tonight.

&&

.MARINE...
Issued at 143 AM CDT Mon Aug 24 2026

Northwest winds of 15-22 kts continue north of Sturgeon Bay early
this morning, with a few gusts to 25 kts near Death`s Door. The
strongest of the winds will continue through sunrise, so will
just let the Small Craft Exercise Caution run its course through
12z. Winds will slowly ease after sunrise.

A period of persistent south/southwest winds is forecast on
Tuesday afternoon into Wednesday. Gusts to 25 kts will be
possible, with waves building to at least 2 to 4 ft with some 5
foot waves possible. A Small Craft Advisory may be needed.
A moderate swim risk is also expected on Lake Michigan beaches.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......Bersch
MARINE.........Bersch

NWS GRB Office Area Forecast Discussion