605
FXUS63 KGRB 190753
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
253 AM CDT Sun Jul 19 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- A plume of wildfire smoke will continue to cycle over the region
  this today. Degraded air quality and visibility are expected at
  times. Additional bouts of smoke are possible during the middle
  of this week.

- Multiple rounds of thunderstorms are likely (60-80%) to impact
  the region Monday into Monday night. 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.
  Craft Advisory likely Monday afternoon into Monday night.

&&

.DISCUSSION...
Issued at 250 AM CDT Sun Jul 19 2026

Thunderstorm/Precip Chances:

Dry conditions will prevail for much of today with upper ridging
over the region. CAM ensembles do show a low-end (15-30%) chance for
scattered showers north of HWY 8 late this evening and overnight,
however, the bulk of this activity is expected to stay in the UP
and over Lake Superior.

Monday continues to be the main focus for thunderstorms over the next
week. The overlap of a seasonally strong upper jet/vort max and
strong instability will set the stage for a potentially significant
severe weather event if conditions ultimately align. However, even
with the supportive synoptic environment there is a high level of
uncertainty with how this event may ultimately unfold.

Digging into more details with Monday`s event the first question
mark of the day will be how morning convection plays out within
the WAA regime ahead of the main wave. CAMs are in generally good
agreement that multiple clusters of storms will develop well west
and north of the forecast area Sunday night with one or two of
these clusters possibly following an instability gradient/LLJ into
north-central WI Monday morning. These storms will likely be on a
downward trend by this time as they will be encountering drier
more stable air, in part due to the lingering presence of wildfire
smoke shrouding the forecast area. However, with elongated
hodographs can`t entirely rule a marginal risk for severe hail or
damaging winds as these storms move east through the morning.
Following the departure of any morning convection attention will
turn to how quickly modified areas can recover instability as well
as focusing in on any outflow/differential heating boundaries due
to debris clouds that could serve as a focus for later rounds of
storms.

Into the afternoon the main upper wave is progged to be dropping over
the MN Arrowhead with the surface front becoming orientate from
northeast MN to northeast SD. Ahead of these features CAMs show a
rapidly destabilizing warm sector as dew points surge into the upper
60s to low 70s and middle level lapse rates steepen. Some CAMs show
initial discrete supercells developing in this warm sector across
western and central WI during the mid afternoon. If these storms
can maintain a discrete nature for a time that is when the tornado
and large hail threat would be maximized. However, the window for
discrete cells may be limited to just a few hours as the
progressive nature of the front as long with likely splitting
cells and storms interactions favors quick upscale growth into one
or move MCS/QLCS structures with embedded bowing segments
becoming the focus for damaging winds swaths and spin up type
tornados. This threat looks like it will persist all to the way to
the lakeshore, however, CAMs do generally show lower instability
further east so while storms may remain severe some downward trend
with eastward extent is possible. In general the severe threat
looks to be moving out of the forecast area by midnight Monday.

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:

The current round of smoke will stick around through today with
continued impacts of air quality and visibility (less than 3 miles
at times). 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 today 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 potential that the
earlier storms could also be severe, so stay tuned for updates.

&&

.MARINE...
Issued at 250 AM CDT Sun Jul 19 2026

South to southwest winds will increase tonight 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. A Small
Craft will likely (80-90%) be needed Monday afternoon into Monday
night.

Wildfire smoke will also continue to impact Green Bay and Lake
Michigan through 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.....GK
AVIATION.......JLA
MARINE.........GK

NWS GRB Office Area Forecast Discussion