642
FXUS63 KGRB 120359
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1059 PM CDT Fri Jul 11 2025

Updated aviation portion for 06Z TAF issuance
and new information added to update section

.UPDATE...
Issued at 1041 PM CDT Fri Jul 11 2025

Precipitation trends are tough to pinpoint, as showers in NC/C WI
have been more persistent than previously thought, and the area of
rain associated with the MCV and surface meso-low is not as
widespread as expected. Heaviest rains have occurred in C WI,
where a few spots in western Marathon County received 2+ inches
earlier. Not as confident in heavy rainfall chances farther east
due to recent radar trends and a lack of instability (leading to
somewhat lower rainfall rates).

Made some changes earler to add some smoke to the grids in the
wake of the cold frontal passage tomorrow afternoon, and again
during the day on Sunday. WDNR issued an Air Quality Alert to
address this potential.

&&

.KEY MESSAGES...

- Periods of rain and isolated embedded thunderstorms are
  expected overnight. Pockets of heavy rainfall will remain
  possible, but do not expect additional amounts to exceed 1 inch
  through daybreak.

- A few strong to severe storms will be possible on Saturday
  afternoon. Gusty winds, isolated large hail, and heavy
  downpours will be the main hazards with any stronger storms.

- Next round of active weather arrives during the middle of next week.

&&

.DISCUSSION...
Issued at 438 PM CDT Fri Jul 11 2025

Precipitation/Thunderstorm Chances...This afternoon`s water vapor
imagery was showing two features of interest. A developing MCS
was located over eastern IA/southwestern WI/northwestern IL, while
a line of convection developed along a cold front in northern MN.

In the near term, the attention is focused with the developing MCS
as models have trended with a slightly further north track. While
the higher potential for severe weather will remain well to the
south of the forecast area, a threat for a narrow corridor of heavy
rainfall is seeming more apparent as models indicate the deformation
zone of the system will set up somewhere over the area tonight.
There seems to be a general consensus the narrow band will occur
east of a Stevens Point to Iron Mountain line. Within this band, 1
to 2+ inches of rainfall and localized flooding is possible. Even
higher, very localized, rainfall amounts cannot be ruled out given
the abnormal PWATs of 1.75 to 2.10 inches (175-200% of normal for
this time of year). Locations in north-central WI will see the
lowest rainfall amounts (0.50 inches or less). The precip associated
with this system will come to an end Saturday morning as it exits to
the northeast of the region.

The aforementioned cold front in northern MN will be the feature
of concern for Saturday as it tracks across the forecast area.
There is good consensus that a broken line of showers and
thunderstorms will develop along the front sometime midday
Saturday or Saturday afternoon over the area. The front and
convection will exit by Saturday evening. A tongue of 1000-1500
J/kg of MUCAPE, deep-layer shear of 35-45 kts, and steep mid-level
lapse rates will support a marginal severe threat for any of the
storms that develop along the front. However, if there is too much
cloud debris Saturday morning from the overnight precipitation,
this may hinder some of the instability for the afternoon. If
strong or severe thunderstorms develop, damaging winds, large
hail, and brief heavy downpours will all be possible.

Following the cold front, models continue to show subtle indications
of a weak boundary sweeping across the area late Sunday or Monday,
which could bring light precip and thunderstorm chances. Otherwise,
sometime midweek will be the next chance for widespread
precipitation and thunderstorms.

Smoke...An area of smoke from Canadian wildfires was observed on
visible satellite imagery this afternoon entering far northwest MN,
following the previously mentioned cold front. Smoke models indicate
a concentrated area of near-surface smoke sweeping across the
forecast area following the front for Saturday and continuing into
Sunday. As a result, coordination with the WI DNR has led to the
issuance of an Air Quality Advisory for the entire state through
noon Monday, with the PM2.5 AQI reaching the Unhealthy for Sensitive
Groups to Unhealthy level.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1041 PM CDT Fri Jul 11 2025

Areas of light to moderate rainfall and a rare rumble of thunder
were reported across the forecast area late this evening. While
most of the area still had VFR conditions, sporadic MVFR
conditions were observed in the western and southern parts of the
forecast area.

Light to moderate rain will continue overnight, with ceilings and
vsbys gradually dropping to MVFR/IFR. locally heavy rainfall may
occur, along with IFR vsbys. Expect the rain to pull out late
tonight into early Saturday, with gradually improving flight
conditions during the mid to late morning. A cold front will move
through the region on Saturday, reaching NC/C WI late morning and
exiting eastern WI by evening. Kept the Prob30`s for thunderstorms
at the eastern TAF sites for the 18z-22z time frame, as the front
moves through during peak heating. Locally strong storms are
possible. Gusty west winds will develop in the wake of the front
on Saturday.

Clearing skies and decreasing winds are expected by sunset.

&&

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

&&

$$

UPDATE.........Kieckbusch
DISCUSSION.....Kruk
AVIATION.......Kieckbusch