029
FXUS63 KGRB 261927
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
227 PM CDT Sun Jul 26 2026

.KEY MESSAGES...

- Heat indices into the middle to upper 90s across central
  Wisconsin this afternoon and early evening, where a Heat
  Advisory is in effect for Wood, Portage, Waupaca, and Waushara
  counties.

- Strong to severe thunderstorms, and heavy rainfall and urban
  and small stream flooding, are possible tonight. There are
  lesser chances for severe storms on Monday. Damaging winds
  and large hail will be the primary hazards.

- A cold front passing through the region will bring a shift to
  northerly winds and relief from the high humidity for Tuesday
  through mid-week, with lower thunderstorm chances until late in
  the work week.

&&

.DISCUSSION...
Issued at 225 PM CDT Sun Jul 26 2026

A weak wave of low pressure over sw Ontario will continue ewd
across nrn Lake Superior this evening along with an area of weak
PVA via vorticity maximums. A little farther to the south, persistent
850-700 mb warm, moist advection will continue across nrn MN to
over Lake Superior this afternoon then gradually shift swd into
Upper MI and nrn WI this evening via wly 850 mb flow of 25-30 kt.

A tongue of projected RAP MLCAPE is expected to rise to 3000-3500
J/KG from wrn WI to just and west of Duluth by late this afternoon
with a high CIN region over ne MN due to cloud cover, then greater
instability with less CIN in sw Ontario. The CAMs due initiate
convection over ne MN this afternoon within this high CIN region,
but it is possible initiation could occur farther to the south
where a weak boundary, from the passing sfc trough to the north,
will separate light wly winds from sswly winds to its south. It`s
also possible the showers and scattered storms over nw MN will
grow upscale when encountering the higher CAPE environment to its
se later this afternoon and evening.

Overall there is much uncertainty on the timing and location this
afternoon and early evening, but will count on the aforementioned
850-700 mb warm, moist advection that will gradually shift swd
across nrn and central WI through the evening and overnight to
bring some clarity to the forecast. MUCAPE should range from
1500-3000 J/KG from east to west across the forecast area tnt,
while the mid level cap likely stays over wrn WI. Some CAMs show
persistent north to south showers and storms from late evening
into Mon AM which agrees well with the persistent warm, moist
advection via wly flow aloft. High PWATs of 1.5-1.8 inches will be
available and will need to message heavy rain and urban and small
stream flooding. The recent dry conditions and the overall uncertainty
precludes the issuance of a Flood Watch at this time.

An Enhanced Risk is outlooked for WI but is counting on a mature
and severe MCS. Deep layer nwly shear of 50 kt is in place along
with the aforementioned values of CAPE and mdt to large DCAPE.
However, if more discrete cells or clusters of cells occur
instead of a large dominant MCS, large hail and damaging wet
microbursts will still remain fairly probable just with lesser
coverage. The tornado threat looks low given relatively weak low
level wind shear.

For Monday low pressure will track from east central MN across
central or srn WI, while a shortwave trough tracks from sw
Ontario into the nrn Great Lakes. Scattered showers and storms may
still be ongoing Mon AM for the overnight hours, but should
mostly dissipate by late morning. New shower and storm development
is expected but will focus over the ern half of the forecast
area. Believe temps will still rebound back into the 80s but there
is much uncertainty given the clouds and precipitation. This will
also affect the potential for severe storms which does look a bit
lower at this time.

Afterward, this low pressure area and upper wave will occlude
and remain over portions of the Mid Atlantic States and New
England for Wed and the remainder of the week. This maintains
nwly flow aloft for the wrn Great Lakes with a sfc ridge
residing over the area for Tue nt-Thu. Shortwave troughs in the
flow aloft will then bring 40-50 percent chances for showers and
storms Thu nt-Sat. High temps in the lower to middle 80s are
expected for much of this period.


&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 218 PM CDT Sun Jul 26 2026

for 18Z TAF Issuance
Issued at 105 PM CDT Sun Jul 26 2026

Scattered fair weather cumulus fields will be present during the
early afternoon but are expected to diminish shortly as capping
and mixing arrive across the area.

The main concern will be the formation of strong to severe
thunderstorms this evening, which will dive southeast from the
arrowhead of Minnesota into Wisconsin. Maintained the approximate
timing of the first wave of convection across the forecast area.
Expect low visibility and ceilings with the strongest storms,
bringing conditions to IFR. Additionally, severe storms may also
include strong wind gusts and large hail. Behind this initial
line, additional rain and storms may develop along an axis from
northwest to southeast across the region. Amount of additional
thunder with the active weather remain uncertain at this time, but
will need to watch for any additional stronger storms.

A relatively short period of quieter weather is then possible
across the middle part of the day Monday before we again look
ahead towards additional storms Monday evening.

.KOSH...

Scattered to few cumulus clouds are on their way out this morning
as skies clear. Strong capping will then keep skies clear into the
evening.

The chance of thunderstorms will increase this evening when
clusters of storms pass across the region. Maintained the TEMPO
group from the previous routine TAF as the timing window has
changed little. Once storms develop far to the north across the
arrowhead of Minnesota this afternoon, the timing should be able
to be narrowed from the 4 hour group currently in the TAF.

Thunderstorms will be capable of producing strong surface wind
gusts over 40 knots, LIFR visibilities, and IFR ceilings in the
strongest activity.

Additional showers are also likely to follow, which may maintain
the lower ceilings across the area through the overnight hours
into Monday.

&&

.MARINE...
Issued at 225 PM CDT Sun Jul 26 2026

Light to modest sly winds this afternoon and evening will shift
wly late tnt into Mon AM, then back to southeasterly for Mon
afternoon. Nly winds will then develop Mon nt-Tue with waves
increasing to 2 to 4 feet. Patchy fog could develop at times
into tnt.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory until 9 PM CDT this evening for WIZ035>037-045.
MARINE...None.

&&

$$

DISCUSSION...MG
AVIATION...Uhlmann
MARINE...MG