NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 100702
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
202 AM CDT Wed Jun 10 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Multiple rounds of strong to severe thunderstorms through this
  evening. There is no one time frame of the day and evening that
  is more favored than others for thunderstorms. There is an
  enhanced risk for severe weather as storm complexes move
  through, including damaging winds, large hail, and an isolated
  tornado.

- Additional strong to severe thunderstorms are expected Thursday
  afternoon into Thursday evening.

- Heavy rain is an increasing hazard today through Thursday.
  Localized flooding is expected where heavy rain occurs.

- Dense fog over northeast WI to Lake Michigan this morning will
  create hazardous travel conditions.

- Very warm and humid through Thursday. Peak of heat today with
  heat indices potentially into the lower 90s if there is enough
  break in between rounds of storms. Cooling trend later this
  weekend into next week.

&&

.DISCUSSION...
Issued at 200 AM CDT Wed Jun 10 2026

Main changes: Plethora of upstream convectively induced shortwaves
has resulted in multiple waves of storms today. Given instability
building in over the area, any of these rounds of storms could be
strong to severe. First round arrives over much of the area
through mid morning, with additional round moving in earlier in
the afternoon. A potential third round could impact the region
this evening. All severe hazards still could occur. No change
there. However, given multiple rounds of storms with heavy rain,
risk of flooding will increase where episodes of heaviest rain
overlap. HREF 95th percentile for 24hr rainfall ending at 7am on
Thursday shows widespread net of 3-4 inches of rain, maximized
over central WI where there is better chance of multiple rounds of
heavy rain.

Severe and Heavy Rain Potential Through Tonight...First up is
squall line over eastern Dakotas, arcing into southern MN. Complex
is on leading edge of mid-upper jet and on nose of 60+ kt low-
level jet just upstream of MLCAPEs of 4000j/kg. CAPE gradient
shifts northeast into WI by 12z as warm front arrives. 00z HRRR
and ARW matching reality best and show this line of storms into
central/north-central WI by 12z supported by sufficient 0-1km
shear downstream of the building instability. Severe thunderstorm
watch is in effect until 7a into western WI. Expect the storms
to cross northern WI this morning (exiting by 10-11a) with severe
winds a possibility.

Next round of storms then looks to arrive earlier, during the
mid to late afternoon with genesis region in western IA this
morning as next shortwave/increasing H5 jet interacts with
reservoir of untapped instability ahead of approaching cold front.
If something close to the decently agreed CAM guidance is
correct, severe storms may be breaking out over central WI by
early this afternoon, with the main line moving through soon
thereafter. No real change in very favorable, high-end parameter
space for developing storms to interact. MLCAPEs over 2500J/kg,
mid-level lapse rates over 7c/km and very ample CAPE in hail
growth favor very large hail while mid-level dry air and DCAPE up
to 1000 j/kg lead to damaging winds. Backed flow in low-levels,
likely due to earlier day convection/outflows, results in 0-1km/0-3km
SRH that favors the potential for tornadoes, especially with
discrete cells that form in the afternoon. Additional convection
could occur in bows/lines into the early evening, but trying to
get specific how that will unfold is pretty dicey given there could
be multiple complexes of storms that occur before then that will
no doubt impact the ambient convective environment. The best advice
today is to keep up to date with the forecast as it will be changing
based on near term trends, and have multiple ways to receive warnings.

Again, given the multiple rounds of heavy rain could see the need
for a flood watch later today once it becomes clearer where swaths
of heavy rain set up and if they overlap in similar areas. Currently
HREF PMM/LPMM 24hr rainfall ending at 7am on Thursday suggest the
most likely areas to see 2+ inches with maxes up to 4 inches will
be over portions of central to north-central WI. WPC highlights
almost all of our area in a Slight risk for Excessive Rainfall.
Typically when we have a Slight Risk we will see at least isolated
flash flooding occur. Just where that occurs in this scenario will
be the primary question.

Otherwise for today, given the multiple rounds of storms, think
it is going to be a challenge to realize heat index values
flirting with upper 90s to near 100. Forecast temps have been
lowered, with most spots remaining in the 80s. And, some models
would indicate that may be even optimisitic, for at least some
areas. Fog near Lake Michigan and over northeast WI is expected to
fade by late morning, but convection during the morning and outflows
could alter that idea along the lake. Will be yet another something
to keep eye on today as it leads to hazardous travel with the
lower visibility and will have direct impact on instability that
is present this afternoon. A lull still looks to be in store later
tonight after convection ends by late evening. Still warm and humid
with patchy fog.

Severe and Heavy Rain Potential Thursday...No large change in
the idea that a second and more potent shortwave tracks toward the
region on Thursday afternoon, causing an associated surface low
to lift northeast directly into southeast or east-central
Wisconsin by Thursday evening. Widespread showers and
thunderstorms will accompany this system, fueled by a deep plume
of moisture with precipitable water values climbing well above
normal. Severe threat may develop in the afternoon over east-
central Wisconsin where instability increases to around 1000 J/kg
under strong deep layer shear of 50 to 60 kts. At current,
greatest risk for severe wind and the potential for tornadoes may
remain just south of Fox Valley/lakeshore. However, probabilty for
hail would be maximized due to the strong shear and sufficient
instability. That said, will not take too much of a jog north in
the effective warm front to put all severe hazards in play over
especially central and east-central WI on Thursday. Other issue
will be heavy rain. Signal that showed up yesterday on NBM and
LREF remains in place this morning, with widespread higher-end
percentiles depicting at least 2 inches of rain along and just
north of the track of the sfc low, with 95th percentile showing
2.5 to 3.5 inches for the far southern portions of the area. These
amounts would easily lead to urban or low-lying flooding if they
impact the Fox Valley. Depending on rainfall amounts today and
tonight, these areas could be looking at the need for a flood
watch on Thursday.

Convection will wind down by mid-evening following the passage of
a strong cold front. A much cooler and drier weather pattern
will return to the western Great Lakes Friday into early next week
as a broad longwave trough sets up from the Hudson Bay down into
the region. On the southern periphery of this cold pool aloft,
spotty diurnally driven showers and storms look possible on Friday
and Saturday afternoons. Saturday still standing out as having
the slightly better potential for scattered afternoon showers and
storms due to the passage of a secondary cold front and building
daytime instability as highs now look to reach back into the lower
80s in parts of the area. In fact, higher end CAPEs around 1000
J/kg now shown could result in at least a small shot of isolated
severe potential given enough shear. Will be something to keep
eye on in the coming days.

By Sunday and early next week, behind the front dry air and
persistent high pressure will take hold, dropping temperatures
slightly below seasonal normals.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1040 PM CDT Tue Jun 9 2026

Latest guidance/observations continue to show dense fog expanding
across far northeast WI and the lakeshore. Model visibility
forecast shows the greater potential for widespread dense fog east
of an Eagle River to Antigo to Oshkosh line overnight. The fog
will likely become more widespread dense as you get closer to the
bay and Lake Michigan. Late tonight into Wednesday morning, the
first round of thunderstorms will push northeast across the area.
Still some uncertainty in how quick the morning convection will
clear out, but another round of strong or severe storms is
expected later Wednesday afternoon into Wednesday evening. Large
hail of 1" or greater and wind gusts over 50 knots are possible
with this cluster of thunderstorms.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CDT this morning for WIZ013-021-
022-039-040-050-073-074.
&&

$$

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