723
FXUS63 KGRB 240906
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
406 AM CDT Tue Jun 24 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Much cooler temps today through Thursday, but it will remain
  quite muggy, especially today across the south.

- Periodic chances of showers and thunderstorms will continue
  today through Friday morning.

- Periods of heavy rainfall are possible at times Wednesday and
  Thursday. Probability of receiving over 2 inches is highest
  (20-40%) across central WI.

&&

.DISCUSSION...
Issued at 405 AM CDT Tue Jun 24 2025

Short Term...Today...Tonight...and Wednesday

Storm / Heavy Rain Threats: Cold front has made its way well south
of the area overnight and will reside in southern WI or northern
IL the next couple of days. This will keep any severe weather
threat very low as better surface instability will remain to our
south. However, some elevated instability (up to ~900 J/kg,
highest over the south) will be present to keep at least some
isolated to scattered showers and stray storms around, especially
this morning into the early afternoon and along/south of Hwy 29.
By later this afternoon, northeast winds will usher in some more
stable air, ending the threat for showers/storms for most spots.
Additional shower/storm activity will spread back into the area
on Wednesday as another push of higher PWATs and shortwave/FGEN
forcing arrive. PWATs between 1.5-2.0" and warm cloud depths to
~14,000 ft will bring a heavy rain and localized flooding threat
to any location that sees repeated showers/storms (or that
received the heavier rain the last 24 hours, especially Waushara
Co.), but the overall flooding threat looks low through mid-
afternoon Wednesday.

Temps / Humidity: It will be much cooler today and Wednesday with
highs mainly in the 70s. Some 60s are expected near the immediate
showers of Lake Michigan. It will remain muggy to start the day,
then dewpoints will drop from north to south through the day,
bringing more comfortable humidity levels later today into
Wednesday. Lows tonight will be quite refreshing for some, with
upper 40s and 50s over far northern WI, with lows near 60 over
central WI and the Fox Valley. The east/northeast flow on
Wednesday will hold high temps mainly in the upper 60s and 70s.

Long Term...Wednesday Night Through Monday

Mid-level fgen and an anomalously moist airmass (PWATS 1.8-1.9")will
combine to produce periods of moderate to heavy rainfall Wednesday
evening through Thursday morning. Ensemble and deterministic guidance
both suggest the heaviest rainfall will occur generally along a
corridor from southeast MN to central WI. Within this corridor NBM
probs for 24 hour rainfall greater than 1.5" are 40-50% across
central WI and decrease to 20-40% further east. The risk for any
embedded thunderstorms through Thursday morning is low as the better
instability is shunted south of a stalled frontal boundary forecast to
set up across southern WI.

Isolated to scattered thunderstorms do look slightly more favorable
late Thursday afternoon and evening as instability builds to 600-
1000 J/kg ahead of an approaching cold front. 0-6km shear is also
forecast to reach 30-40kts which may help any thunderstorms that do
develop become more organized. With precipitation loading and 500-
700 J/kg DCAPE there will be a risk for a few strong microburst wind
gusts, however, confidence any wind gusts reach severe criteria is
low. In addition to the wind, long skinny CAPE profiles and near
climatological max PWATS ~ 1.9" support a risk for heavy downpours
and isolated flood concerns. Will need to monitor antecedent soil
moisture from prior rainfalls to determine what areas may be most at
risk of flooding.

Behind the aforementioned front the region is forecast to dry out to
end the week and start to weekend. However, the dry weather does not
look like it will stick around for long. ML/AI convective hazard
forecast show an increase chance for more thunderstorm activity
Sunday into early next week. Ensemble mean 500mb flow also supports
a chance for thunderstorms during this period with a deepening
trough moving over the upper Midwest.

Temperatures through the extended period will slowly start to warm
backup with highs returning to the middle to upper 80s by this
weekend. However, lower humidity levels should keep heat indices
from feeling as oppressive as the past few days,.

&&

.AVIATION.../00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1106 PM CDT Mon Jun 23 2025

Challenging aviation forecast. A large swath of light rain with
sparsely embedded thunder is setting up to impact all sites
except for KRHI. KAUW and CWA on northern edge... expecting no
thunder at those sites.

All sites except for KRHI are slated to drop to MVFR. Held off
on any IFR for now, as confidence is not high enough. Will
monitor for fog potential overnight at all sites not KRHI. IF
fog develops, expecting vsbys of 4 to 6 miles at this time.

&&

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

&&

$$

DISCUSSION.....Bersch/GK
AVIATION.......Kotenberg