970
FXUS63 KGRB 262321
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
621 PM CDT Thu Jun 26 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- There is a slight risk of severe thunderstorms in central Wisconsin
  and the southern Fox Valley late this afternoon and evening.
  Damaging winds and a few tornadoes are possible. The greatest
  threat is expected southwest of a line from Marshfield to
  Oshkosh. Severe weather will be most likely between 4 pm and 10
  pm.

- A Flood Watch has been issued for central Wisconsin and the
  southern Fox Valley, where soils are already saturated and
  additional rainfall amounts of 1.5 to 3 inches are expected.
  Areas with greatest flood potential include low-lying and urban
  areas, though localized river flooding may also occur.

- Near/below temperatures continue through Friday, then increasing
  heat and humidity into the weekend, with highs near 90 by
  Sunday.

- There is a chance of strong to severe storms late this weekend,
  especially Sunday afternoon and evening.

&&

.DISCUSSION...
Issued at 259 PM CDT Thu Jun 26 2025

Forecast concerns include severe weather and flooding potential
through this evening, and another couple rounds of strong to
severe storms from Saturday night through Sunday evening.

Heavy Rainfall/Flooding Concerns: Will continue the Flood Watch
for Wood, Portage, Waupaca, Waushara and Winnebago counties from
4 pm today through 4 am Friday. Much of this area has received
1.5 to 3 inches of rain since Monday, so soils are saturated. A
west to east line of storms extending from KLSE-KDLL-KUNU will
continue to lift north into our southern counties between 4-5 pm,
followed by a well-developed squall line crossing central and east
central WI from 6-10 pm. Both of these lines will be capable of
producing torrential rainfall, given PWATs approaching 2 inches,
and enough elevated instability to support higher rainfall rates
with convection. The end time of the watch is likely longer than
it needs to be, as most of the heavier rain will be gone by late
evening, but wanted to match the end time of ARX`s Flood Watch to
our southwest.

Severe Weather Threat Through This Evening: Most models keep the
warm front and associated surface based instability south of the
forecast area late this afternoon/evening, but given the close
proximity of the front (shallow stable layer near the surface),
MUCAPE of 500-1000 j/kg, deep layer shear of 40-45 kts, 0-3 km
SRH of 200-300 m2/s2, there is potential for supercells with
damaging winds and a few tornadoes, especially in our far
southwest counties. CAMs show development starting in our far
southwest by 4-5 pm. A squall line will also move through C/EC
from west to east between 6 and 10 pm, with potential for sporadic
strong to damaging gusts.

Rest of the Forecast: Quieter conditions expected friday and
Saturday, with warmer temperatures in the 80s arriving for the
weekend. A weak cold front is expected to approach the region
Saturday night, then move through on Sunday and Sunday night, and
this should bring a good chance of storms. With SBCAPE rising to
2-4k j/kg on Sunday, there is ample instability to support severe
storms. However, deep layer shear is on the weak side; around
20-25 knots. Drier and more comfortable condiitons are expected
for much of the following work week.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 621 PM CDT Thu Jun 26 2025

Generally poor flying conditions will move into the region during
the TAF period from heavy rain and thunderstorms this evening,
rain overnight, and low ceilings and fog by Friday morning.

Most locations have MVFR to IFR ceilings moving into the region as
showers and thunderstorms move in. Thunderstorm extent northwards
seems uncertain, so only made brief mention for RHI. May need to
extend thunder in this region if storms can work their way
northwards, but certainty isn`t high. Elsewhere a band of
thunderstorms will work its way across the region through the
early overnight. Kept a TEMPO group in place for the main period
of scattered thunderstorms this evening.

A low stratus deck plus recent rain will likely lead to IFR and
possibly even LIFR from fog in the morning hours Friday before
some improvement is possible by the late morning to early
afternoon. Most locations will still be sitting at MVFR by the
early afternoon hours on Friday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 4 AM CDT Friday for WIZ035>037-045-048.
&&

$$

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