195
FXUS63 KGRB 171128
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
628 AM CDT Fri Jul 17 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Air quality and visibility will continue to be degraded by
   smoke from wildfires burning across northern Minnesota and
   southwest Ontario through this morning. Smoke will start to
   clear from west to east through the day.

- Isolated to scattered thunderstorms are expected this afternoon
  and evening (60-80% chance). A few storms could become strong
  to severe, mainly across northern WI, with threats of damaging
  wind gusts, hail, and locally heavy rain.

- Another round of thunderstorms is possible (50-70% chance)
  Monday. There is increase confidence that a few of these storms
  could be strong to severe.

&&

.DISCUSSION...
Issued at 141 AM CDT Fri Jul 17 2026

Smoke Trends...Blanket of dense wildfire smoke continues to sit over
the region early this morning impact air quailty and visibility.
Expectations is that has winds veer around to the southwest today
smoke will clear out from southwest to northeast. For areas in
central WI clearing is expected to begin late this morning (9-11AM)
while areas in far northeast WI and along the lakeshore may not see
much improvement until 7-9PM this evening. Unfortunately, the
reprieve from the smoke will be relatively short as RAP/HRRR/RRFS
show a second wave of smoke overtaking much of the forecast area
Saturday as winds turn northwesterly behind a cold front. There is
some uncertainty with how dense this second round of smoke may be
due to fire behavior over the next 48 hours, but smoke models are
generally less aggressive with concentrations this weekend that what
we have seen the last two days.

For next week periods of smoke may continue to cycle over the region
any time winds are persistently our of the northwest to northeast,
while persistently southerly winds will bring generally more clear
conditions.

Thunderstorm Chance...Mid-level WV imagery shows a few subtle short-
waves moving across western and central WI early this morning
spurring on a few isolated showers. As these waves move east some
CAMs show an increase in showers this morning over east-central and
northeast WI where surface winds are more convergent. However, with
a lack in instability don`t expect much organized thunderstorm
development with this round.

A second period of isolated thunderstorms is possible this
afternoon, mainly across northern WI as a deepening low over Ontario
draws a warm front northward. South of this front increase
instability is expected with MLCAPE increase to 1000-1500 J/kg. An
upper jet streak will also result in increase deep layer shear and
elongated hodographs which could aid in storm organization and lead
to at least an isolated hail and damaging wind threat. However,
forcing for ascent appears limit through this afternoon, so it may be
a struggle to get any storms to fully take advantage of this
environment.

Third period of note today is late this evening and overnight as a
sharp cold front sweeps across the area. There is uncertainty with
how any preceding convection may modify the environment, but CAMs
show enough instability to support scattered thunderstorms along and
ahead of the front some of which may be strong to marginally severe.
Low level shear will be maximized across northern WI, near the
intersection of the warm and cold fronts. It is this area where
there is a low-end (2% chance) for a brief tornado with any storms
along or just ahead of the front, however, LCLs are rather high
(1000+ m) which due to the dry boundary layer which does limit the
tornado threat. As storms move east overnight they may tend to
become more elevated with hail and sporadic damaging wind gusts
becoming the main hazards. Once these storms clear the area tonight
dry conditions are expected through for the weekend.

Monday will be the next day to focus on for possible thunderstorms
as a dynamic upper short-wave/anomalous jet streak are progged to
eject southeast out of the Canadian prairie and across the western
Great Lakes. As these features overspread the region deep layer
shear will increase to 45-50kts. At the surface southwesterly winds
will increase through the day and advect a plum of upper 60s to low
70s dew points into the region. This moist air mass will be
overspread by an EML with steep mid-level laps rates resulting in
strong MUCAPE values (2000+ J/kg). The combination of strong
instability and shear will create a parameter space supportive of
strong to severe thunderstorms Monday afternoon into Monday night.
However, exactly how convection will evolve is uncertain as dominate
storm mode is uncertain. Additional there is some uncertainty with
how any elevated smoke could impact destabilization during the day.

Beyond Monday shower and storm chances are low (10-15%) through much
of next week as a drier air mass settles in over the forecast area.

Temperature Trends...With southerly winds today and clearing smoke
temperatures will trend hot again with highs forecast to reach the
upper 80s to low 90s this afternoon. Behind a cold front temps will
moderate, but remain a few degrees above normal this weekend. Monday
will see similar temperatures as today as southerly winds help highs
back into the upper 80s. A cooler, drier airmass is then favored by
the middle of next week leading to generally at or slightly below
normal temperatures.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 627 AM CDT Fri Jul 17 2026

Smoke will continue to be the main aviation impact this morning as
it creates IFR/MVFR vsbys at all terminals. As winds turn S/SW later
this morning, the smoke will begin to clear from southwest to
northeast through the afternoon. Surface obs may also continue to
show MVFR ceilings at times, however, many of these ceilings are
tied to smoke rather than clouds. Other VFR/MVFR clouds will
continue to push across the area this morning as a area of showers
and storms slowly spreads across the area.

For the aforementioned showers have TEMPO groups with -SHRA through
14Z, but with limited instability and recent satellite trends have left
thunder out of the TAFs for now. Another round of storms is expected
to drop south across the region this evening into tonight, mainly
between 02-08Z. There is a low (15%) chance for a few of these
storms to become strong to severe, mainly across norther WI which
could impact RHI. If any stronger storms develop strong wind gusts
30-40kts and hail would be possible.

S/SW winds of 5-15 kts are expected through much of the day today.
Overnight winds will shift to the NW behind a cold front and may
gust up to 20kts.

.KOSH...

IFR visibilities from smoke will continue to impact KOSH this
morning. Smoke will clear out at OSH this afternoon, likely between
18-21Z. However, thicker smoke is likely to move back into the area
at times this weekend as flow turns back to the north. Surface obs
will also continue to show MVFR ceilings at times, however, these
ceilings are tied to smoke rather than clouds. Other VFR/MVFR clouds
will push across the area this morning associated with an area of
showers moving across the region.

For the showers this morning did include a TEMPO group through 14Z
for light rain, but left thunder out of the TAF based on limited
instability and recent satellite trends. Another round of showers
and storms is possible late this evening/overnight as a cold front
pushes south. There is uncertainty if any storms will hold together
far enough south to impact OSH, so for now have a PROB30 group for
light rain after 07Z.

S/SW winds of 6-13 kts are expected through much of the day today.
Overnight winds will shift to the NW behind a cold front and may
gust up to 20kts.

Looking ahead smoke will be the main aviation impact this weekend
with otherwise dry conditions. There is an increase chance for one
or more rounds of thunderstorms to move across the Fox Valley on
Monday.

&&

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

&&

$$

DISCUSSION.....GK
AVIATION.......GK

NWS GRB Office Area Forecast Discussion