295
FXUS63 KGRB 311204
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
704 AM CDT Mon Aug 31 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Isolated showers and a few non-severe storms this morning. Small
  chance (20-30%) for showers and storms this afternoon and
  evening. If storms develop, they may become strong or severe,
  capable of producing hail, damaging winds, and torrential
  downpours.

- Warm, humid conditions continue into Tuesday. Heat indices in
  the 90s expected this afternoon, and again for some locations
  on Tuesday.

- Conditional threat for hazardous boating and swimming conditions
  on Lake Michigan this afternoon. Dense fog possible at times on
  Lake Michigan through Tuesday.

&&

.DISCUSSION...
Issued at 248 AM CDT Mon Aug 31 2026

Precipitation/Storm Trends...Isolated showers prevailed across
portions of central and east-central WI early this morning where an
850mb jet was increasing within an area of WAA, while a narrow line
of elevated thunderstorms developed over the WI/Upper MI border and
exited the region to the northeast where an area of steeper mid-
level lapse rates, 850mb f-gen, and another area of 850mb WAA
prevailed. As the 850mb jet continues to increase within the area of
WAA over central and east-central WI this morning, anticipate the
shower activity increasing into northeast WI before exiting east by
9 AM. Despite up to 1000 J/kg of MUCAPE and effective shear around
30 kts, expecting only a few elevated, non-severe storms within the
shower activity. If anything, the showers will produce brief heavy
downpours with PWATs near 2.00 inches.

Once the morning shower activity ends, much of today will be dry as
a weak capping inversion will be in place. However, some CAMs/short-
range models indicating a brief period when the cap may break during
the afternoon/evening producing isolated showers/storms as a weak
low-pressure system and associated weak cold front move over the
region. If this cap can break, convection will develop in a rather
unstable and moist atmosphere with MUCAPE of 2000-3000 J/kg, deep-
layer shear of 35-45 kts, and dew points in the upper 60s to low
70s. If any storms can develop, there will be a marginal threat for
strong/severe storms capable of producing hail around 1 inch and
damaging winds, in addition to torrential downpours. SPC has a
Marginal risk for severe storms over much of the forecast area,
except north-central WI. A few elevated storms may linger into the
evening, but coverage looks limited.

The aforementioned weak cold front/boundary will sag south into
Tuesday and hover just to the south of the forecast area for
Tuesday, leaving dry conditions in place for most of the day.
Chances for showers and storms then return Tuesday evening/night as
the frontal boundary lifts north aided by mid-level forcing from an
approaching mid-level shortwave. Shower/storm chances will continue
into Wednesday as the shortwave moves over the region. A couple
shortwaves then look to move over the region through the remainder
of the work week and into the start of the weekend, bringing
intermittent chances for showers and storms at times.

Temperatures/Humidity...Summer continues! A rather hot and humid day
is expected with dew points in the upper 60s to low 70s as high
temperatures climb into the mid 80s to low 90s. This will result in
afternoon heat indices in the low to mid 90s. Some spots may even
see heat indices in the upper 90s if temps or dewpoints slightly
over perform. Despite the cold front moving over the region this
evening, temperatures on Tuesday will be only a few degrees lower
than today. It will also still be humid on Tuesday, as dew points
remain in the 60s to low 70s, but locations in north-central WI may
see a little relief with dew points forecast in the low 60s.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 704 AM CDT Mon Aug 31 2026

LIFR/IFR clouds continued across northern WI this morning,
sneaking into the central WI TAF sites within the past hour as
surface winds were from the east. As winds turn southerly
throughout the morning, these clouds will lift north and gradually
rise/dissipate, leaving VFR conditions across all TAF sites by
midday. Hi-res models indicate isolated showers and storms
developing over central and far northeast WI late this afternoon
and tracking southeast into this evening. Confidence is not high
in these isolated showers or storms moving directly over any one
terminal, so have included PROB30s for -SHRA at all TAF sites with
most confident timing. If one of these showers or storms move
over a TAF site, a brief reduction in visibility to IFR is
expected with the potential for strong wind gusts and hail.

Forecast confidence for late tonight decreases as guidance is not
in agreement with the potential for cigs and vsbys dropping to
MVFR/IFR. For now, have TEMPO groups at all TAF sites.

Winds will turn south this morning, then turn southwest by midday.
A weak cold front is expected to move across the region this
evening, causing another wind shift to the northwest. Overall,
winds will stay under 15 kts for today, before becoming light and
variable by late tonight.

&&

.MARINE...
Issued at 248 AM CDT Mon Aug 31 2026

Southerly winds are expected to increase again today, gusting to
around 20 kts, building waves to around 3-4 ft with a few waves to
5 ft within the nearshore waters along Lake Michigan. This will
bring a conditional threat for hazardous conditions to small craft
and a moderate risk of rip currents along Lake Michigan beaches.
Based on how Sunday`s marginal winds/waves performed in a similar
pattern, decided not to issue any headlines. There will also be a
slight offshore component to the wind today, which may keep the
higher waves just offshore. With dew points in the upper 60s to
low 70s through Tuesday and water temps in the upper 50s and 60s,
some dense fog will be possible at times. Any fog threat should
end as winds turn offshore Tuesday night.

&&

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

&&

$$

DISCUSSION.....Kruk
AVIATION.......Kruk
MARINE.........Kruk

NWS GRB Office Area Forecast Discussion