943
FXUS63 KGRB 190301
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1001 PM CDT Sat Jul 18 2026

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 848 PM CDT Sat Jul 18 2026

Widespread smoke has descended upon northeast WI this evening,
with many visibilities now down to 1-2 miles. Nowcast AQI from
airnow.gov shows air quality has become degraded to the very
unhealthy category (purple) from northern WI into eastern WI.
Based on these trends, increased smoke coverage to widespread rest
of tonight. Based on recent runs of the RRFS which is doing okay
with the extent/concentration of the smoke, could see visibilities
drop to less than 1 mile into northern WI rest of the night.
Forecast trends do continue to suggest we will see gradual
improvement with the smoke on Sunday, but it may not occur until
the afternoon hours. Even with the improvement, it does not look
like the smoke will completely clear out.

&&

.KEY MESSAGES...

- Another plume of wildfire smoke will continue to spread across
  the region this afternoon/evening. Smoke will then likely cycle
  around the region through the weekend. Degraded air quality and
  visibility are expected at times.

- A round of thunderstorms is likely (60-80%) to impact the region
  Monday into Monday night, with a severe weather event becoming
  more likely. There is a level 3 out of 5 severe thunderstorm
  risk Monday afternoon/evening.

- Dense marine smoke is expected to continue at times into Monday.
  An area-wide Small Craft Advisory will likely be needed Monday
  afternoon into Monday night.

&&

.DISCUSSION...
Issued at 337 PM CDT Sat Jul 18 2026

Shower/Storm Potential: CAMs are getting a little more aggressive
with bringing in some showers and possibly a storm over northern
WI Sunday afternoon as activity from northeast MN spills into Lake
Superior and northern WI. Don`t expect much fanfare with this
activity, but did add some slight chances PoPs over the far north.

Monday into Monday night is still looking like the most active
day of the week with thunderstorm activity likely at some point
during the day/night, as an upper level vort max and seasonally
strong jet streak are forecast to move across the state. South
winds will usher in a pretty moist airmass, with dewpoints
climbing into the upper 60s to lower 70s, and PWATs approaching
1.75". The vort max, steep mid-level lapse rates, mid-upper jet
and CAPEs building to at least 2000 J/kg will make for a favorable
environment for severe storms. However, storm scale details such
as timing, storm mode, and convective evolution remain a little
uncertain, especially with some questions on debris clouds,
morning convection, and smoke which could limit destabilization.
In addition, some capping could be present, which would aid in
holding the activity in check. But a higher end event appears
possible, especially if we miss out on the early morning activity,
with the area maxing out instability in the later afternoon as
the best dynamics arrive and the cap breaks. Elongated hodographs
will favor supercells and bowing segments, with a tornado threat
as well, especially near the onset of the storms, if we archive
the higher levels of instability. The development of a QLCS with
pockets of higher end wind damage and some spin ups, will also be
possible. SPC`s has bumped up our area in an Enhanced Risk, which
seems reasonable due to the dynamics/instability in place.

Behind this front, drier weather is expected for mid-week as high
pressure builds in with gusty northerly winds on Tuesday. Next
chance for showers and storms looks to arrive late Thursday into
Friday.

Smoke Trends: Relief from the smoke was rather short-lived as
winds shifting back to the north/northwest behind the front has
brought an additional plume of smoke into the region. This batch
will stick around through the weekend, but HRRR and RRFS surface
smoke forecasts show this round being a little less intense than
this past Wednesday/Thursday (with no 1SM VSBYs noted in our area
so far today). Still, impacts to air quality and visibility (down
to around 2 miles) are expected. An Air Quality Advisory is in
effect statewide through noon Monday. Additional plumes of smoke
may impact the region Tuesday into Wednesday, as flow turns back
to the north/northwest behind a frontal boundary. A little tough
to forecast the smoke that far out, as fire behavior will
determine just how much smoke there is to spread into the region.

Temp Trends: Despite the smoke, seasonably warm temperatures are
expected to continue through the weekend under surface high
pressure, with less humid conditions. A day of humid conditions is
expected ahead of the front on Monday, then more pleasant
conditions return mid-week as stronger cold advection will occur
behind the frontal passage, with near to below average temps for
at least a day or two.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1000 PM CDT Sat Jul 18 2026

Smoke persists rest of tonight, before slowly diminishing through
Sunday afternoon. Visibility of 1-3SM and a broken-overcast layer
of 025-035 will be common with the smoke, but actual conditions
will be variable. Visibility will improve to 3-5SM by Sunday
afternoon, with a broken layer of 035-050, scattering out by late
day. Smoke Sunday night will be more variable, but still could
see vsby down to 3SM at times.

An isolated shower or storm may occur late Sunday afternoon
into Sunday evening over far northern WI. More widespread storm
chances arrive after midnight Sunday night on into Monday and
Monday night. Some storms Monday into Monday night could be
severe.

Expect winds from the E-SE less than 10 kts rest of tonight,
before shifting to the SW at 10 kts or less Sunday into Sunday
night.

.KOSH...

Smoke layer will persist through the night with vsby 2-3SM and a
broken-overcast layer 030-050. Slow improvement will occur on
Sunday with vsby increasing to 3-4SM in the morning, and to 5-6SM
in the afternoon. Any associated broken-overcast layer will abate
in the afternoon. Smoke on Sunday night will be more variable, but
still could produce vsby down to 3-4SM at times.

ENE winds around 10 kts through the early overnight hours will
diminish to less than 5 kts late tonight while shifting ESE. Winds
on Sunday will increase to 5-8 kts from the SE by the afternoon,
veering to the S by Sunday evening.

Looking ahead, preliminary indications are that the earliest time
thunderstorms could move into Oshkosh would be late morning on
Monday. A greater chance for thunderstorms, some of which could
be severe, would be late Monday afternoon into Monday evening.
This timing could change and there is some potenital that the
earlier storms could also be severe, so stay tuned for updates.

&&

.MARINE...
Issued at 337 PM CDT Sat Jul 18 2026

North/northeast will continue to gust to around 25 kts into the
early evening hours, then will ease through the mid and late
evening. South to southwest winds will increase Sunday night into
Monday, with gusts to 30 kts likely Monday afternoon. Waves on
Lake Michigan will build to 4-7 ft on Monday, and to 2-4 ft on
the bay. The current Small Craft Advisory goes until 7pm, with
another one likely for Monday afternoon into Monday night.

Wildfire smoke will continue to impact Green Bay and Lake Michigan
this afternoon into at least Monday morning, dropping visibilities
to around 1NM at times. Some smoke models want to nudge the thicker
smoke just west of the waters, but with the marine inversion in
place, the smoke will likely get trapped. Have extended the Marine
Dense Smoke Advisory through noon Monday.

&&

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

&&

$$

UPDATE.........JLA
DISCUSSION.....Bersch
AVIATION.......JLA
MARINE.........Bersch

NWS GRB Office Area Forecast Discussion