393
FXUS63 KGRB 072252
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
552 PM CDT Sun Jun 7 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Warm moist airmass moving over Lake Michigan may bring a period
  of marine dense fog across the nearshore zones through early
  this evening. Patchy fog will may also move in over the
  lakeshore counties at times.

- Above normal temperatures persist for the next week. High
  temperatures in the 90s paired with increasing humidity will
  result in potential for moderate to major heat-related impacts.

- Record to near-record high temperatures are possible Wednesday
  afternoon.

- Chance for widespread showers Monday and Monday night.
  Increasing storm potential during the middle to end of the week.

- Strong to severe storms are possible late Wednesday afternoon
  into Wednesday evening. The best chance will be west of the Fox
  Valley.

&&

.DISCUSSION...
Issued at 105 PM CDT Sun Jun 7 2026

Fog...The fog bank over the middle of the lake has finally made
it to the nearshore zones, mainly south of Kewaunee. Hi-res models
have been absolutely terrible in modeling what will happen with
this fog bank; therefore, confidence in its future placement is
rather low. Current thinking is the fog bank should mix out this
evening as winds increase across the lake. Satellite observations
indicate this is already happening with the fog mixing out from
north to south. Will keep the Marine Dense Fog Advisory for the
lake through early this evening and assess as time goes on for a
possible early cancellation.

Temperatures...Though warming trend remains in place for the
upcoming week as heat ridge builds, gradually becoming less
confident in seeing higher end heat indices (100+) during the
middle to end of week timeframe. NBM seems to be coming in a few
degrees hot with highs in the low to mid 90s during this time,
though LREF ensemble shows mean temperatures in the mid to upper
80s with a fairly tight interquartile spread. Current thinking is
that shower and storm chances in/around the area would hamper
temps from rising to their full potential, though predictability
of storm placement/coverage is low this far out. Nevertheless, can
expect well above average (5 to 10 degrees) highs as subsidence
under mid-level ridge brings 850 mb temps between 22 and 25C down
to the surface. Would venture to say that headlines will be
necessary at some point during the middle of the week given
widespread moderate (level 2) to major (level 3) risk for heat-
related impacts. If current temperatures hold, record to near-
record high temperatures will be within reach Wednesday afternoon.

Rain/storm chances...A chance (60 to 90%) for widespread rain
arrives Monday into Monday night as a fairly potent shortwave
migrates through prevailing southwesterly flow and up into the
Midwest. PWATs range between 1.75 and 2" during this time, nearing
the absolute max relative to climo, so safe to say that periods
of heavy rain can be expected. However, rain seems to have a more
stratiform appearance during this time since organized convection
appears unlikely due to absence of upper support and lack of
surface forcing mechanism. However, embedded thunder will be
possible as modest instability (~500 to 700 J/kg) pools near
central Wisconsin. Any convection would be efficient rain
producers in this moisture-rich environment, so will have to
monitor for higher-end rainfall (1+") in this scenario. As it
stands now, probabilistic guidance retains a 40 to 70% signal for
receiving 0.5" of rain. Even at the higher end amounts, the
flooding threat is not expected to be significant as soil moisture
percentiles across much of the region are below 30% with much of
the area in the D0 drought monitor so a heavy rainfall can likely
be soaked in rather efficiently by the ground.

Active pattern takes shape during the middle to late part of the
week as upper flow re-amplifies and several shortwaves propagate
over the northern CONUS.

Severe weather risk...While the severe weather risk for the middle
to late part of the week isn`t clear, there is increasing
confidence for strong to severe storms late Wednesday afternoon
into Wednesday evening. The cold front moving through the western
Great Lakes region is moving through during a favorable time, late
afternoon into the evening, and has sped up from previous runs.
In addition, MUCAPEs are forecast to be around 2000 J/kg with bulk
shear values ranging from around 25 knots in the Fox Valley to
closer to 50 knots across north-central Wisconsin. Model soundings
show thick CAPE in the Hail Growth Zone along with 1000 J/kg of
DCAPE, indicating large hail and damaging winds are possible.
Abundant low level turning in the hodographs and LCL heights
below 1000 m indicate tornadoes are not out of the question.

The best potential for severe weather appears to be in the
western portion of the CWA out in central and north-central
Wisconsin given the earlier timing where instability and shear
will be maximized. The severe weather threat drops off as you go
further east towards the Fox Valley and lakeshore given less
favorable shear and a later arrival of the storms, which would
mean instability would not be as high. The timing of the front
will play a large role, so any further adjustments in the timing
of the front will alter the severe weather risk Wednesday
afternoon and Wednesday evening.

Another round of storms is slated to move through the region on
Thursday. However, the severe weather potential for this day will
likely hinge on what happens with the system on Wednesday and
Wednesday night. Therefore, it is too early to ascertain what will
happen this far out.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 547 PM CDT Sun Jun 7 2026

VFR conditions will continue into Monday morning as mid and high
clouds will continue to be on the increase overnight. A band of
showers will move across the area later Monday morning into the
afternoon. May need to add thunder in the 06z tafs for KAUW/KCWA.
There will be a break in the rain behind the first round, with a
steadier round of showers and storms later in the afternoon into
the evening. CIGS are likely to drop into the MVFR or lower
category later Monday afternoon and Monday night. Fog will be
possible Monday night.

&&

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

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Eckberg

NWS GRB Office Area Forecast Discussion