115
FXUS63 KGRB 101935
AFDGRB

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

Forecast discussion for routine afternoon forecast 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 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
  warmer and more humid conditions along with a chance of storms
  returns late in the week.

&&

.DISCUSSION...
Issued at 232 PM CDT Sun Aug 10 2025

Remnants of MCV that moved out of Iowa late last night have
largely fizzled out while shifting into central and northeast WI.
This is due in large part to debris light showers and clouds from
the very heavy rainfall that occurred in southern WI last night
holding down the instability farther to the north. We remain ahead
of primary cold front over MN and in a very moist airmass with
PWAT this morning at GRB of 1.78 inches. Main concerns are
convective trends rest of the afternoon into this evening as
shortwave and cold front approach from the west. Next opportunity
for strong to severe storms will be Tuesday.

Precipitation/Thunderstorm Trends...Quiet currently with just a
few light showers north and east, but watching showers and storms
forming in area of greater instability over MN/IA. As these track
across especially southern half of the area after 5-6 pm through
midnight, could see some thunder. Given the juicy, moisture laden
airmass present, any storm could produce heavy rain. If the storms
cross the more hydrophobic areas of the Fox Valley, especially if
they train, then urban flooding could occur. This seems like a
very low risk at this time given the expected coverage of any
thunderstorms. After midnight the showers and storms will be
exiting. Areas of fog may form late tonight again, especially
northwest of the Fox Valley. In wake of the shortwave moving
through tonight and associated cold frontal passage, Monday has
trended drier. Retained smaller chances for showers and storms,
especially during peak heating of the day as MLCAPES rise to
500-1000J/kg and another wave approaches from the central plains.
Better focus for precipitation could end up just being restricted
to far southern and southeast areas.

Still keeping eye on Tuesday as approach of sharper mid-level
trough will increase shear to 35+ kts. Stronger dynamics, including
RRQ of upper jet, along with building instability coming together
during peak heating ahead of a cold front could support risk for
at least isolated severe storms during the afternoon. Machine
learning output not too excited, but the large scale pattern
suggest at least some potential. Will highlight this mention in
HWO.

After the cold front moves through Tuesday night, high pressure
will bring drier and more comfortable weather for Wednesday and
Thursday. The break will be brief as another warmer, more humid,
and potentially active severe weather regime develops again Friday
into next weekend.

&&

.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.....JLA
AVIATION.......JLA