692
FXUS63 KGRB 112359
AFDGRB

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

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Rain and non-severe thunderstorms are expected this evening and
  overnight. A narrow band of heavy rain (1-2 inches) is possible
  east of a Stevens Point to Iron Mountain line, which may result
  in flooding of urban and low-lying areas.

- A few strong to severe storms will be possible on Saturday.
  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 00Z TAF Issuance
Issued at 644 PM CDT Fri Jul 11 2025

Scattered showers and a few thunderstorms continued over NC/C WI
early this evening, within an instability axis. A line of severe
thunderstorms was ongoing over southern WI. In between, an area of
light to moderate rain was spreading into our southern counties,
in response to an approaching short-wave/MCV. Most observing sites
were reporting VFR conditions.

Expect the convection over our western counties to weaken early
this evening, as daytime instability wanes. Otherwise, look for
steady light to moderate rain to overspread the southeast two-
thirds of the forecast as the MCV and associated weak surface low
move through this evening/overnight. Once this occurs, ceilings
and vsbys are expected to drop to MVFR/IFR. There may be a locally
heavier band of rain east of a Stevens Point to Iron Mountain
line, though a lack of instability may limit convective
contribution and limit rainfall rates. expect the rain to pull
out overnight 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. Added 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.

&&

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

&&

$$

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