291
FXUS63 KGRB 191630
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1130 AM CDT Sun Jul 19 2026

Updated aviation portion for 18Z TAF 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 18Z TAF Issuance
Issued at 1108 AM CDT Sun Jul 19 2026

At KOSH...high pressure across eastern Wisconsin as resulted in
poor mixing this morning, thus slower improvement in visibilities.
Visibilities should slowly improve this afternoon up to 3 to 4
miles by late afternoon. Watching cumulus field to the east of the
airfield which was moving westward, but was struggling to
maintain a broken deck. Have included a tempo group for MVFR CIGS
between 2,500-3,000 feet until 21z. Otherwise, areas of smoke will
continue tonight with visibilities between four and six miles. On
Monday, the first cluster of showers and thunderstorms will
approach the site between 16z-18z Monday. Currently have a PROB30
group for this event as the showers and storms will be on the
weakening trend, and it is possible the showers and storms could
dissipate or move just south of the airport. Also, the weakening
showers may also produce gusty winds from the northwest for an
hour Monday morning, which is not in the 18z TAF. Later Monday
afternoon into the evening, will need to watch round of strong or
severe storms across northeast WI. These storms have the
capability of producing a high end wind event with gusts of 60+
knots along with large hail and torrential rainfall.

For the rest of northeast WI, smoke will continue to gradually improve
through the afternoon and tonight. Some patchy MVFR CIGS will
likely rise into the VFR category this afternoon. The first round
of showers and storms will move into central and north-central WI
after 13z, then continue to move southeast and weaken through the
late morning. Some stronger storms with hail and gusty winds are
possible in north-central and central WI. Meanwhile, later Monday
afternoon and evening, a round of strong or severe storms is
expected with large hail, a high end wind event of gusts of 60+
knots and heavy rainfall.

&&

.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.......Eckberg
MARINE.........GK

NWS GRB Office Area Forecast Discussion