967
FXUS63 KGRB 101821
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
121 PM CDT Sun Aug 10 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Chances for thunderstorms late this afternoon through the
  evening. Main hazard will be torrential rainfall and localized
  urban flooding. The overall severe risk for today has decreased.

- Small chance for showers and storms on Monday, especially in the
  afternoon. Greater chance for storms setting up for Tuesday
  afternoon when conditions look more favorable for at least
  isolated severe thunderstorms.

- Dry weather and more comfortable humidity arrives mid-week, but
  more humid conditions and a chance of storms return late in the
  week.

&&

.DISCUSSION...
Issued at 436 AM CDT Sun Aug 10 2025

Areas of dense fog developed overnight, prompting the issuance of
a Dense Fog Advisory for much of central, north central and far
northeast WI. Some improvement has been noted on the southern and
eastern side of the advisory, and if this continues, a portion of
the advisory may be cancelled early. Increasing WAA and moisture
convergence was resulting in an uptick in elevated convection in
the far southern part of the forecast area, where MUCAPE of
1000-1500 j/kg and PWATs of 1.75 to 2.00 inches resided early
this morning. Looking upstream, WV imagery showed a huge MCS and
associated MCV moving from eastern NE into southwest IA. This MCV
is expected to track northeast through the GRB forecast area this
afternoon.

Precipitation/Thunderstorm Trends...Expect showers and storms to
gradually expand northward this morning and early afternoon,
initially due to WAA and moisture convergence on the nose of a
25-35 kt LLJ, then later in response to the arrival of the NE/IA
MCV. Have gone with likely pops as the MCV moves through. Despite
abundant cloud cover, models show CAPE increasing to about
800-1300 j/kg this afternoon, which should allow for a few strong
thunderstorms to form. The modest instability, combined with deep
layer shear of 20-30 kts, should limit the overall severe threat,
but isolated marginally severe storms with damaging winds are
possible. With PWATs in the 1.75 to 2 inch range lingering over
the southeast part of the forecast area, will also likely see
pockets of heavy rainfall and an isolated flooding risk for urban
areas in C/EC WI. Will continue to skew pops from lowest
northwest to highest southeast tonight into Monday with respect
to moisture and instability gradients.

Tuesday could be an interesting day, as a stronger cold front,
short-wave trough, RRQ of an upper jet, CAPE of 1000-2000 j/kg and
much stronger deep layer shear of 40-45 kts move through the
forecast area during peak heating. This will be a day to watch for
potential severe thunderstorms.

After the cold front moves through Tuesday night, high pressure
will bring drier and more comfortable weather for Wednesday and
Thursday. As the high shifts east late in the week, more humid air
returns, along with the chance of thunderstorms.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 115 PM CDT Sun Aug 10 2025

Low cigs (MVFR) have retreated to far northern WI. Otherwise,
even with some light rain lifting over especially east-central WI,
conditions have trended to VFR. First wave of showers expected to
exit east-central WI by mid afternoon. After a break, expect a
loosely organized cluster of showers and maybe some thunder to
push across the area in the 22z-04z window. Main hazard with any
TSRA will be brief heavy rain, but confidence is low in coverage
of these storms. Later tonight, after showers diminish, another
round of low stratus and fog will be possible, especially northwest
of the Fox Valley/lakeshore areas. Lowest VSBY in this set of TAFs
will be at RHI/AUW/CWA, but MVFR VSBY may occur at other TAF sites
as well.

Small chances for showers on Monday, probably most likely mid to
late afternoon during peak heating. After any stratus and fog
depart, conditions expected to be VFR through the day.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......JLA