386
FXUS63 KGRB 270913
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
413 AM CDT Fri Jun 27 2025

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Near/below temperatures continue today, then increasing heat and
  humidity into the weekend, with highs in the 80s to near 90 on
  Sunday.

- There is a chance of strong to severe storms late this weekend,
  especially Sunday afternoon and evening. Heavy rain and
  localized flooding is also possible.

&&

.DISCUSSION...
Issued at 412 AM CDT Fri Jun 27 2025

Today: Surface low pressure, cold front and mid-level shortwave
will slowly exit the area this morning, with lingering light
showers ending from southwest to northeast. A stray thunderstorm
will remain possible as some elevated instability will reside
ahead of the front. Recent rain and lighter winds will allow fog,
locally dense (especially across central WI), to continue in spots
this morning as well. Cyclonic flow will keep clouds around
most/all of the day, with west/northwest wind gusting to 25 mph.
Temps will remain below normal with highs ranging from the 60s
across north central WI to the 70s over central and eastern WI. It
will remain on the muggy side across eastern WI ahead of the
front, with more comfortable conditions arriving from west to east
through the day.

Severe Storm Potential & Increasing Heat/Humidity This Weekend:
Most/all of Saturday is looking dry as high pressure shifts into
the eastern Great Lakes. However, will need to monitor for a dying
complex early in the day, then more shower/storm develop later in
the day along a weak frontal boundary lingering across the state,
as some of the CAMs want to initiate of activity along it, but
won`t bite on that just yet. More widespread shower and storm
development is expected to our west Saturday PM/night where the
LLJ interacts with the frontal boundary and a large pool of CAPE
over 3000+ J/kg. This area/complex looks to be organized enough to
move into parts of central and/or north central WI late Saturday
into Sunday morning, but likely weakening as it tracks east. Some
gusty winds and heavy rain would be the main threats. Attention
then turns to Sunday as a mid- level trough digs into the northern
Plains and a cold front tracks across the state. Impressive
instability forecast to build ahead of the front, with 3000-4000
J/kg of SBCAPE. Deep layer shear is still forecast to be on the
weaker side (20-30 kts), especially the further south you go,
which would hinder better organization. But up to 40 kts of shear
could be realized later in the day across central and north
central WI, which would favor supercells and bowing segments and
an organized severe weather event (with all hazards possible).
AI/ML convective outlooks continue to highlight our area as well.
SPC has placed much of the area in a Slight Risk for severe storms
on Sunday, which seems very reasonable given the strong
instability.

Temps and humidity levels will be on the rise this weekend as
south flow prevails across the western Great Lakes. Highs in the
upper 70s and low 80s (away from Lake Michigan) are expected on
Saturday with humidity levels climbing through the day. A warm and
humid day on Sunday is expected with highs in the 80s to around
90 with dewpoints in the mid 60s to low (possibly mid) 70s,
producing heat index values in the low to mid 90s for parts of
central and eastern WI.

Flooding: Cancelled the flood watch earlier as the heavier rain
exited the area and only lighter rain expected the rest of the
morning. Other than some rising rivers (especially the Yellow and
Wisconsin) and possible minor flooding due to the recent
rain/runoff, no other flooding concerns are expected the rest of
the week. Bouts of heavy rain are possible this weekend as PWATs
climb back to around 1.5" and at least a round or two of
convection is looking more likely. The convection on Sunday will
be fairly progressive, which should limit the overall flooding
threat. However, if/where any places get multiple rounds of storms
and/or training cells, some additional minor flooding concerns.
This will be especially the case for locations that received the
heavier rain over the past few days.

Rest of the Forecast: As the large trough drops across the Great
Lakes on Monday, expect some clouds along with a few showers in
the northwest/cyclonic flow regime. Models are not in the best
agreement the rest of the week, but additional chances for
showers and storms look return at times as the boundary will set
up somewhere to our west/south.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1038 PM CDT Thu Jun 26 2025

Generally poor flying conditions will remain in the region
overnight, but some improvement is expected by the the afternoon
on Friday.

Rain will continue in the early overnight hours but thunder will
mainly only linger on in east-central Wisconsin before departing
to the east. Ceilings will remain low, ranging from IFR to LIFR,
especially if fog develops overnight under the low clouds.

Winds will increase in the morning hours again, which will help
lift some ceilings and disperse any fog. Better flying conditions
are expected by the end of day Friday.

&&

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

&&

$$

DISCUSSION.....Bersch
AVIATION.......Uhlmann