117
FXUS63 KGRB 161138
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
638 AM CDT Sat Aug 16 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Another thunderstorm complex is expected to impact the region in
  the late morning to early afternoon. Severe storms are possible
  with damaging winds, hail, and heavy round.

- Additional scattered thunderstorms are possible in the late
  afternoon across portions of central to east-central Wisconsin. Severe
  storms and localized flooding remain possible.

- Sunday may see a break before another round of heavier rainfall
  arrives in the late evening.

- With high rainfall rates likely in any storms, the risk for
  flooding may increase if repeated rounds of storms impact the
  same areas. Probabilities for at least 2 inches of rain are 20
  to 60% from now through Monday morning, with the highest
  probabilities in central Wisconsin.

&&

.DISCUSSION...
Issued at 327 AM CDT Sat Aug 16 2025

Precipitation trends remain the main forecast concern for the next
few days as an active weather pattern remains in place over the
Great Lakes. In addition to occasional strong storms, there is a
lingering heavy rainfall threat as heavy rain potential remains in
place over the course of several days.

Storms Today and Tonight...
Behind the initial rain from the overnight period, some quieter
conditions are expected to linger across the region for the early
to mid morning period before ongoing warm air advection brings
showers back into the region. Attention then turns to an upstream
MCS over the Dakotas early this morning associated with a notable
shortwave in the mid levels. As this system propagates eastwards,
would expect it to follow along the instability gradient across
Minnesota into Wisconsin, possibly lifting northwards slightly due
to the southwesterly flow in the low to mid levels. Many CAMs
have also latched on to this signal, suggesting an arrival of the
thunderstorm complex sometime in the late morning to early
afternoon. As the complex gets develops eastwards into eastern
Wisconsin it will get away from the better instability, which
should lead to some weakening. Therefore, the better potential for
any strong or severe storms will remain focused towards central
Wisconsin, but isolated wind gusts cannot be ruled out further
east. From there, guidance does hint at some redevelopment in the
late afternoon as the shortwave progresses southeastwards along
the remaining instability gradient across central to east- central
Wisconsin, but that will depend heavily on any lingering outflow
from the midday convection. By the evening, convective activity is
expected to largely push the more unstable airmass into southern
Wisconsin. If this occurs, much of Saturday night may be dry for
most of the region. It`s worth noting however that some storms may
still get into portions of central Wisconsin, especially if any
organized cold pool from today`s storms ends up being more
disorganized. Heavy rain potential remains present in the area,
with a 50-70% chance of getting more than an inch of rainfall
along much of central to east-central Wisconsin. The localized
high end amounts are also still in the 2-3 inch range, but getting
to these totals would likely require redevelopment to occur over
the same areas that receive the midday MCS, and therefore only
represent a 5-10% chance at any one location.

Sunday`s Storms...
Sunday`s details will largely depend on the preceding overnight
details and where the boundary of the warmer and more moist air
sits during the daytime. For the most part, models agree that the
more moist and unstable airmass will not shift much over the
course of the day, but disagree on where exactly that boundary
will be. If it does set up south of our area Saturday night, most
of Sunday will indeed by dry as well. However, if it lingers
across portions of central Wisconsin, some rain and thunderstorm
activity can still be expected across portions of the area. No
larger organization is anticipated for the daytime however. The
main focus for Sunday will come along the next fast moving
shortwave that will be supported by a modest low level jet and
mid-level warm air advection during the late evening to overnight
period, which will again serve to organize some more widespread
rainfall and storms in the region. Fortunately, this time period
will fairly starved for instability and upper support, so severe
potential remains low. Heavier rainfall will be more limited on
Sunday than today do to the relatively more limited instability,
but thru remains a region of 40-60% chance of exceeding an inch
in portions of central to north-central Wisconsin. Despite this,
the overall flooding potential is helped some by the possible
quiet period from the overnight through much of Sunday.

Monday... An upper low will follow the Sunday night activity,
crossing the region Monday. Confidence on this time period is low,
but there would be enough dynamics around to support some
additional storm development in the afternoon as instability
increases once more. Shear values during this timeframe remain
relatively weak, but lapse rates would support some larger hail
and possibly a few wind gusts.

Rest of the Forecast...
Quieter weather conditions are then finally expected by the
middle of the week, with drier conditions forecast to linger on
through the remainder of the work week into the beginning of next
weekend.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 638 AM CDT Sat Aug 16 2025

Main aviation concern today will be the arrival of a complex of
thunderstorms in the late morning to early afternoon (16Z-19Z)
from west to east. These storms will bring some MVFR to IFR
ceilings, low visibility due to rainfall, and some strong wind
gusts. Kept a TEMPO to time out the main period of storms. Behind
this initial round, some redevelopment will be possible in the
late afternoon and evening for portions of central to east-central
Wisconsin, although confidence is not high on the exact timing.
Included a PROB30 for any redevelopment in this period. Finally,
forecast has trended drier for the overnight period, with rain
largely getting out of the forecast period for tonight, although
some lower MVFR cloud cover may return.

&&

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

&&

$$

DISCUSSION.....Uhlmann
AVIATION.......Uhlmann