955
FXUS63 KGRB 030907
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
407 AM CDT Wed Sep 3 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Showers and a few embedded thunderstorms expected this morning.
  No severe storms are expected. Light showers to continue in
  north-central Wisconsin through tonight.

- Colder air arrives today into tonight. Record lows temps
  possible tonight, with record to near-record low max temps
  likely Thursday and Friday. Below normal temps to continue
  through the weekend.

- Another round of rain arrives Thursday evening and lingers into
  early Friday. This system will also bring gusty winds on
  Friday.

&&

.DISCUSSION...
Issued at 406 AM CDT Wed Sep 3 2025

Short Term...Today...Tonight...and Thursday

Shower/Storm Trends: A couple areas/broken lines of showers will
spread west to east across the area this morning as a cold front
and shortwave move through, and an upper low drops into southern
Canada. MUCAPEs up to 600 J/kg will still reside ahead of the
front, so a few non-severe storms will be possible through the
morning hours. A few post-frontal showers/sprinkles/drizzle will
be possible, along with some instability showers this afternoon,
mainly across central and north-central WI. The most widespread
coverage (50-75%) will be over north-central WI, where northwest
winds flowing over Lake Superior will produce some lake-enhanced
showers. This activity will continue over far north-central WI
into tonight, then taper off overnight.

Temperatures & Frost Potential: The well-advertised cool down
starts today as CAA spread across the region behind the cold
front and an unusually cold airmass settles over the Great Lakes.
Morning highs are likely for most spots today (50s far north, 60s
elsewhere), with steady or slowly falling temps this afternoon as
the stronger CAA arrives. It will be much colder tonight with
lows in the 30s to low 40s for most spots, with some warmer
readings in Door Co. Have continue to mention patchy frost over
much of central and north-central WI. However, prospects for
widespread frost will be hindered by clouds and winds (especially
just off the surface) keeping things mixed enough to limit frost
production. That said, the NBM has the highest probabilities
(20-40%) of getting below freezing across Marathon Co., which
could occur if winds decouple and clouds clear sufficiently. A
Frost Advisory may be needed where this occurs. We will be
approaching some record low temps tonight, with most sitting in
the 30s. Wausau may be the most achievable with a record low of
37, and should have the lighter winds and fewest clouds. Thursday
will be a chilly day with highs in the 50s to low 60s, along with
a west wind gusting to 25 mph. Record low max temps for Sept 4
will be in jeopardy, as all sites have records in the mid 50s to
60.

Long Term...Thursday Night Through Tuesday

Precipitation Chances...A quick-moving low pressure system will
dive  southeast across the Dakotas/MN into WI by Thursday
evening, track across the state, and depart to the east by late
Friday morning. Despite slight disagreements with the exact track
of the low, widespread rainfall is expected. Rainfall amounts
should remain less than 1 inch (and likely below 0.75 inches)
given PWATs of 0.75-1.00 inches. Additional light rain showers are
possible in far north- central WI on Friday with lingering low-
level moisture and slightly favorable west-northwest winds. Models
indicate additional light shower activity on Saturday associated
with a weak embedded mid- level shortwave, but impacts will be
minimal. Dry weather results Sunday into Monday as surface high
pressure shifts over the area. Models then indicate the next
chance for precip sometime midweek.

Wind...Accompanying the quick-moving low pressure system will be a
tight pressure gradient with strong southwesterly low-level winds
ahead of the low Thursday evening, turning westerly with CAA on
Friday. As a result, gusts of 25 to 35 mph are possible throughout
this time frame, with the highest gusts on Friday. Winds will
subside Friday evening.

Temperatures...An abnormally cold airmass will remain in place
through Saturday, leaving some record low highs potentially in
jeopardy for Sept 5 (Friday). Friday`s high temperatures will be
about 15 to 20 degrees below normal with values ranging from the
low  50s to low 60s. Temperatures will gradually warm by a few
degrees each day throughout the weekend and into early next week,
but will overall remain below normal.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1029 PM CDT Tue Sep 2 2025

One area of showers is exiting far northeast Wisconsin late this
evening. Meanwhile, a more potent line of showers and storms is
progressing southeast over northwest WI at about 25 kts and will
reach RHI at about 05z at its current speed and heading. Some
weakening is expected by the time this line reaches RHI, which
should continue as it moves into northeast WI. Confidence is low
that this line will reach central WI and the Fox Valley.

Another round of showers is expected to moved across the region
between 10-16z Wednesday. This round will likely be more
widespread (60-80% chance). Ceilings will quickly lower as these
showers and associated cold front move through, with most
locations lowering to MVFR/IFR. In addition, there may be some
minor vsby restrictions due to the showers. A slow improvement in
flight conditions is expected during the late morning or early
afternoon hours on Wednesday, but most places will probably not
reach VFR before 18z Wednesday. North- central WI may remain MVFR
through much of the afternoon.

Widely scattered shower activity is expected to redevelop over
central and north-central WI on late Wednesday afternoon as a
potent upper low draws near and end by mid-evening. Clearing is
then expected to arrive from west to east by late evening.

Steady but light southwest winds will persist into the early
overnight, then become gusty from the west to northwest in the
wake of the frontal passage Wednesday morning. Winds will remain
gusty through the rest of the TAF period.

&&

.MARINE...
Issued at 406 AM CDT Wed Sep 3 2025

Southwest winds will continue to gust up to around 20 kts early
this morning ahead of a cold front. This will keep waves mainly in
the 1-4 ft range. Winds will shift to the northwest late this
morning and afternoon, with forecast soundings showing gusts to
25 kts likely as the stronger CAA arrives. Highest winds will
likely be on the bay and near Death`s Door where the waters are
the warmest. Will hoist a Small Craft Advisory for this afternoon
for these locations. Another period of gusty southwest/west winds
are expected on Thursday evening into Friday, with a Small Craft
Advisory likely being needed. A few gale force gusts to around 35
kts are possible on Friday as well with NBM probabilities for
gales of 40-70% along the nearshore waters.

As for waterspout potential, will continue to carry a chance this
morning as the cold front works across the bay/lake. As the front
exits to the east, the waterspout threat will be non-zero due to
the colder air aloft, but think the better chances shift over the
open waters and Michigan shorelines as an inversion will limit
better convective cloud heights from materializing, so will not
include this afternoon into tonight. There is another small chance
for waterspouts late Thursday into Friday morning as another low
pressure system tracks through the area.

&&

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

&&

$$

DISCUSSION.....Bersch/Kruk
AVIATION.......MPC
MARINE.........Bersch/Kruk