450
FXUS63 KGRB 170641
AFDGRB

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

Forecast discussion for routine morning forecast 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 06Z TAF Issuance
Issued at 958 PM CDT Thu Jul 16 2026

Smoke will continue to be the main aviation impact overnight into
Friday morning. The smoke will continue to create IFR/MVFR vsbys
into tonight, but as winds turn S/SW on Friday, the smoke will
exit the area from southwest to northeast through the late morning
and 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 late this evening as a area of showers and
storms slowly spreads into the area.

In addition to the smoke, the area of showers and storms over
central WI will continue to slowly work northeast toward the
area. Have continued with TEMPO groups for showers overnight into
early Friday. But confidence remains low if any thunder will
impact the TAF sites, so will not include any thunder after 06z.
Will continue to monitor trends. Additional isolated to scattered
showers and storms will move into central and north central WI
Friday evening.

Light winds are expected overnight, with S/SW winds of 5-15 kts
expected on Friday.

.KOSH...

IFR visibilities from smoke will continue to impact KOSH overnight
into Friday morning, then the smoke will move out of the area
Friday afternoon. The 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 late this evening
associated with the area of showers and storms to the west.

Models continue to indicate that scattered light showers and
isolated storms are possible after midnight through Friday
morning. Will continue with a TEMPO group for showers from 09-
13z, but spotty additional activity is possible later in the day.
But most of the day does look dry.

Light winds are expected tonight, with S/SW winds of 6-13 kts
expected on Friday.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion