NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 182037
AFDGRB

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

Forecast discussion for routine afternoon forecast issuance

.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.
  A Small Craft Advisory is in effect north of Sturgeon Bay until
  7 PM this evening, with an area-wide Small Craft Advisory likely
  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 18Z TAF Issuance
Issued at 123 PM CDT Sat Jul 18 2026

A SCT/BKN cu field with cloud bases of 3000 to 5000 ft AGL
prevailed across the region early this afternoon. Meanwhile,
wildfire smoke dropping from the north was causing MVFR/IFR vsbys
across most TAF sites. Northerly winds this afternoon were gusting
to 15 to 20 kts.

Anticipate the cu field to dissipate into this evening, but the
smoke may keep cigs around 3500 ft AGL late this evening and
overnight. The northerly winds will decrease and turn
northeast/east into this evening and overnight. Winds then turn
south/southwesterly by the end of this TAF period. Additionally,
vsbys will remain in the MVFR/IFR category due to the smoke but
may lift to 6SM or above Sunday morning when guidance indicates
some relief, mainly for the east-central WI TAF sites.

.KOSH...

SCT clouds around 4500 to 5000 ft are anticipated this afternoon
with northerly winds gusting to around 16 kts. However, vsbys are
expected to decrease to MVFR due to smoke dropping south over the
area. Decided to have vsbys as low as 3SM starting at 22z today,
but this may have to be lowered to IFR depending on how thick the
smoke becomes upstream. Vsbys look to increase to at least 6SM
Sunday morning, but the smoke will still be around on Sunday. The
northerly winds will decrease and turn northeast/east this
evening, becoming southerly towards the end of this TAF period.

&&

.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.

&&

$$

DISCUSSION.....Bersch
AVIATION.......Kruk
MARINE.........Bersch