579
FXUS63 KGRB 070630
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
130 AM CDT Sun Jun 7 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Warm moist airmass moving over Lake Michigan may bring a period
  of marine dense fog across our nearshore zones this morning.
  Patchy fog may also develop over the lakeshore counties.

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

- Next chance for widespread showers will be Monday into Tuesday.
  Increasing storm potential during the middle to end of the week.

&&

.DISCUSSION...
Issued at 1238 AM CDT Sun Jun 7 2026

Fog... Areas of fog have developed over the open waters of Lake
Michigan overnight, with high-res guidance retaining a signal for
the fog bank retrograding into our nearshore zones later this
morning. Night fog product shows signs of this already happening
as winds turn more easterly, so will hold onto the Marine Dense
Fog Advisory for the time being. Fog should then burn off within a
few hours of sunrise.

Temperatures... Though warming trend remains in place for this 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.

Rain/storm chances... Next chances (60 to 90%) for widespread
precip arrive Monday into Tuesday 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.

Active pattern takes shape next week as upper flow re-amplifies
and several shortwaves propagate over the northern CONUS.
Becoming increasingly more concerned about severe weather
potential during the middle to end of the week as surface low
spins up over the northern Plains and cold FROPA interacts with
reservoir of surface-based instability over the Midwest. ML
guidance and SPC Day 4-8 Outlook already highlight severe
potential over Wisconsin on Wednesday and Thursday, so will bear
monitoring as we get further into the week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1011 PM CDT Sat Jun 6 2026

Patchy fog is possible across the north OVERNIGHT, mainly in the
MVFR category although could not rule out some IFR CIGS/VSBYs.
Some dense marine fog is possible, especially overnight along the
Lake Michigan shoreline. For Sunday, fair weather cumulus between
3,500 and 5,500 ft is expected during the day. Mid and high clouds
will be on the increase Sunday night. The next chance for showers
and storms will be on Monday.

&&

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

&&

$$

DISCUSSION.....Goodin
AVIATION.......Eckberg

NWS GRB Office Area Forecast Discussion