NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 090703
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
203 AM CDT Tue Jun 9 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Scattered showers with brief heavy downpours this morning,
  especially north-central and northeast WI.

- Storms return late tonight into Wednesday morning. Isolated
  strong to severe storms possible.

- Some severe storms expected late Wednesday afternoon into
  Wednesday evening. Primary hazard over most of the area will be
  damaging winds, though there will also be risk of large hail and
  an isolated tornado.

- Very warm and humid through Thursday. Peak of heat on Wednesday
  with heat index values over 95, leading to moderate risk of heat
  related impacts. Turning cooler beginning Friday.

- Dense marine fog may impact areas near Lake Michigan at times
  through Wednesday.

&&

.DISCUSSION...
Issued at 203 AM CDT Tue Jun 9 2026

Near term through Tonight...Moist southerly return flow ahead of
frontal boundaries over the northern Plains is spurring on
scattered showers iwth locally heavy rain early this morning.
Shortwave lifting over southern WI is enhancing the activity.
Expect the showers to diminish mid to late morning, not before
producing isolated rainfall over 0.50 inch in north-central to far
northeast WI. Sfc wave of low pressure tied to the shortwave will
cross southern Lake Michigan this morning. Main impact will be to
switch winds from E-SE to E-NE this afternoon. Some fog is on the
lake already and as the winds shift, may see fog impact shoreline
of Lake Michigan. If that occurs, temps could trend cooler in the
afternoon compared to the forecast. Otherwise, highs will reach
the lower to middle 80s, warmest over central/north-central WI.

Late this evening and overnight, attention will be on advancing
warm front into western/southwest WI. Effective MUCAPE is healthy
at 1000-2000J/kg with sufficient shear at 20-30 kts. Isolated
strong to severe storms are on the table late tonight into
Wednesday morning as warm front lifts in. CAMS indicate it is
possible that a more organized complex of storms may be over our
area late, instead of isolated storms. Given position of low-level
jet shifting into WI and extent of instability, that certainly is
a potential. Will be a warm, muggy night with areas of fog.

Severe storms and Heavy Rain Potential Wednesday and Wednesday
evening...Though morning convection trends will have some bearing
on how convective pattern evolves later Wednesday into Wednesday
evening, sharp trough, jet energy, and cold front approaching from
the northern Plains interacting with higher-end instability with
CAPE of 2000-3000 J/kg with effective shear of 40+ kts points to
higher ceiling with severe potential on Wednesday. Details not
clear yet, but general idea is still on track with scattered
severe storms developing late afternoon over central MN into
western WI closer to mid-level trough and stronger shortwave
embedded within the flow, with storms then expanding into central
WI early evening, quickly spreading to eastern WI, lakeshore mid
to late evening. Soundings, hodographs point to damaging winds,
large hail initially given elongated hodographs and unidirectional
flow. Once storms grow upscale into a line while sweeping east on
Wednesday evening, QLCS tornado potential is present with expected
0-3km shear vector strong and perpendicular to orientation of the
line. Once the storms get going, models agree to get storm threat
through entire area quickly, with some favoring ending time as
early as 9-10p, and certainly by midnight. Majority of area is
now in Enhanced severe weather risk with higher end severe likely
including wind speeds over 70 mph, hail over 2 inch in diameter
and the potential for an EF2 tornado. Those with outdoor plans on
Wednesday evening, need to start planning for severe weather now.

Despite warm cloud depths to 12kft and PWATs well above the 90th
percentile, and nearing the max for the day, heavy rain potential
on Wednesday evening will be lowered so long as storm motion is
swift. However, MBE vectors less than 5kt point to slow moving
storms/training *if* storms try to backbuild. Max percentiles
(95th percentile to max) from LREF/NBM point to localized high
end rain amounts 2 to 3 inches on Wednesday evening. Will be a
near term nowcast item to monitor on radar.

Another round of storms on Thursday...Even with the storms on
Wednesday evening to the east of the area, we will not be out of
the woods yet in terms of severe/heavy rain potential as primary
trough will still be upstream on Thursday. Decent signal a
stronger wave in the right entrance region of upper jet will
result in more showers and storms crossing the area. Main question
is will severe be main issue (model differences in extent of
instability remaining over the area), or just heavy rain as PWATs
will still be very high. Max percentiles (95th percentile to max)
from LREF/NBM for 24 hr precip ending 12z Friday point to more
widespread high-end rain amounts over 2 inches Thursday into
Thursday evening.

Temperatures...Overall, the theme of models backing off of the
extreme heat that was shown a few days ago continues. Even so,
very warm and humid conditions are expected Wednesday and
Thursday. Based on 850mb temps near 20c if morning storms are not
too disruptive and storms developing in the afternoon occur later
versus earlier, portions of the Fox Valley to far northeast WI
could see high temps into the lower 90s with heat index values
nearing 100. Heatrisk for the day is solidly into the moderate
range. Cannot rule out the need for near term Heat Advisory
headline, but would not say it is likely. On Thursday, highs
reaching the mid 80s with lingering higher dewpoints over eastern
WI will lead to another round of moderate heat related impacts
before showers and storms move in through the afternoon. Heat
backs off by Friday.

Extended...Broad trough remains anchored over upper Great Lakes
through the weekend. Enough lingering moisture and instability to
generate at least small potential for pop-up isolated showers and
storms Friday through the weekend. Even building in higher-end
CAPEs, severe weather looks unlikely. Despite the rain, there will
be plenty of dry time. Temperatures will be closer to normal,
with highs in the 70s. Troughing expands into more of the region
late weekend into early next week, leading to temperatures trending
below normal.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1015 PM CDT Mon Jun 8 2026

Scattered showers will continue overnight into early Tuesday
morning. Could not rule out an isolated thunderstorm, but
coverage and probabilities to low to include in the 06z TAFS. CIGS
also slower drop into the MVFR/IFR category during the evening,
but should drop into these two categories overnight. Patchy fog
may restrict visibilities at times between 06z-13z. Otherwise,
sped up the improving CIGS on Tuesday, reaching the VFR category
Tuesday afternoon. The latest guidance is suggesting fog is likely
Tuesday night and may be dense at times. On Wednesday, strong or
severe storms are possible, especially during the afternoon.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......Eckberg