918
FXUS63 KGRB 291209
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
709 AM CDT Sat Aug 29 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Rain showers to spread across the area this morning into this
  evening. Most locations to see at least 0.20" with the greatest
  potential for localized heavy rainfall (0.50-1") across the
  Northwoods.

- Hazardous boating and swimming conditions on Lake Michigan from
  late tonight through Sunday evening.

- Becoming warmer and more humid Sunday into early next week. Heat
  indices may rise into the 90s Monday afternoon.

- Thunderstorms possible at times from Sunday into early next
  week. It is too early to determine if any of the storms would
  become severe from Sunday through Tuesday.

&&

.DISCUSSION...
Issued at 241 AM CDT Sat Aug 29 2026

Precipitation Trends...The forecast area remains on tracks to see
widely scattered rain showers today as a mid-level shortwave/trough
and weak surface warm front sweeps across the region. Although deep-
layer shear will be around 30-40 kts, a lack in instability (only
around 100 J/kg) will limit thunderstorm chances to only a few
rumbles of thunder at times. As the main area of rain gradually
departs the region to the northeast late this evening, another warm
front will begin to lift into central and east-central WI. Models
seem to be in decent agreement this front will produce additional
isolated/scattered showers and perhaps some elevated storms in these
areas before these showers/storms and the showers in far northeast
WI exit by Sunday morning. PWATs will mainly be in the 1.50-1.75
inch range, but will increase to 1.75-near 2.00 inches with the
arrival of the secondary warm front. CAMs/short-range models
indicate the axis of heaviest rain (0.50-1.00 inches) will be across
the Northwoods, while mid to long-range models indicate the axis
will extend from central into east-central WI. However, ensembles
are trending towards the short-range model solution. Leaned more
towards this solution given the agreement/trends.

The warm front will gradually lift north on Sunday and become nearly
stationary over the area on Monday as an upper-level ridge resides
overhead. This will leave the forecast area in the warm sector with
a surplus of moisture and instability, especially on Monday (MUCAPE
of 2000-3000 J/kg). Models are in disagreement in precip chances for
Sunday, but the greatest chances should remain focused along the
warm front as it lifts north. For Monday, despite the surplus of
moisture and instability, mid-level capping may prevent any
convection from developing. However, there are some signs of a cold
front/shortwave moving over the area sometime later in the day on
Monday, which would present the opportunity for showers and
storms, including strong/severe, to develop. Will need to monitor
these features over the next few forecast runs.

Depending on where/when the aforementioned cold front moves over
the region, models are in some agreement with the front dropping
somewhere over the state and remaining nearly stationary, leading
to additional chances for showers and storms on Tuesday. Another
shortwave then looks to move over the region sometime midweek,
bringing more chances for showers and storms.

Temperatures...Highs will be a few degrees below normal today due to
the anticipated rain/cloud cover, with values in the low to mid 70s.
Temperatures will then rise above normal on Sunday into the upper
70s to mid 80s, and even warmer on Monday and Tuesday with highs in
the mid to upper 80s, due to the persistent southerly flow. This
flow will also result in the return of humid weather on Sunday and
Monday as dew points increase into the upper 60s and low 70s.
Depending on cloud cover and precip chances, heat indices on Monday
may rise into the low to mid 90s. Mother Nature is reminding us
summer isn`t over yet.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 709 AM CDT Sat Aug 29 2026

High and mid-level clouds spread across the region this morning as
isolated showers moved into central and north-central WI. Quickly
following these showers is a larger area of rain that will spread
from west to east across the region throughout the morning. VFR
conditions are mainly anticipated through the duration of this
morning`s rain, but some MVFR vsbys will occur within the heavier
rain showers. However, by midday, MVFR cigs will spread into the
central and north-central WI TAF sites as the rain gradually ends.
Despite the rain ending at the east-central WI TAF sites late
this afternoon/early this evening, VFR cigs should prevail through
the remainder of this TAF period. While the MVFR cigs will remain
in place at the central WI TAF sites through the remainder of the
TAF period, anticipate cigs to drop to IFR/LIFR at the RHI TAF
site around/after midnight tonight with some reductions in vsbys
as well. There are signs of additional scattered showers
developing after 00z Sun, but confidence in coverage at all TAF
sites is low. Have included PROB30 groups when confidence in
showers occurring is greatest.

For both time periods of rainfall, there is a low chance of some
embedded thunder, but confidence is not high enough to include in
this TAF period at this time.

Winds will be from the southwest this morning at 5 to 10 kts, with
a few gusts to 15 kts, before turning southeast this evening.

&&

.MARINE...
Issued at 241 AM CDT Sat Aug 29 2026

Southerly winds will steadily increase late tonight into Sunday,
with sustained winds at 15 to 20 knots along Lake Michigan. These
persistent and gusty southerly winds will build wave heights to 3
to 5 feet along the Lake Michigan nearshore waters, producing
hazardous conditions for small craft. Furthermore, the strong
onshore wave action will generate a high risk of rip currents
along Lake Michigan beaches from late tonight through Sunday
evening. Small Craft Advisories and Beach Hazards Statements will
be needed. Winds and waves are forecast to gradually subside
Sunday evening as the gradient relaxes slightly.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion