884
FXUS63 KGRB 200019
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
719 PM CDT Sun Jul 19 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Level 3 of 5 risk of severe storms Monday, including risk for damaging
  winds, large hail, and a few tornadoes. Highest risk is late
  afternoon and early evening.

- Smoke visibility and air quality impacts continue into Monday.

- Drier and cooler for mid-week.

&&

.DISCUSSION...
Issued at 225 PM CDT Sun Jul 19 2026

Severe Storm Potential Monday:

Anomalously strong deep wind fields for late July combined with
ample instability and ascent from an approaching shortwave trough
and cold front will provide a very conducive environment for severe
storms on Monday.

Early day warm advection driven showers/storms may impact the area,
however these will be ahead of the greater instability, so the
overall severe weather risk appears low during this time.

The higher risk for severe weather will be late in the afternoon
into the evening as forcing from the approaching trough and cold
front increase and erode a stout capping inversion. Overall,
19.12Z convection allowing models suggest generally scattered
storm development after 3 or 4 pm with storms moving
southeastward. Given the elongated hodographs, supercell mode or
bowing segments may be favored with a risk of all hazards,
including hail of at least 2 inches and significant winds. Low-
level winds remain southwesterly, but enough speed shear is
forecast to increase low-level shear. Tornadic potential may be
increased with any right-moving supercells. Some guidance
suggests preferred corridors for more organized storm
development within a broader area from northern Iowa northward
through Wisconsin and the UP. These trends will be evaluated
leading up to the event.

Although high rain rates will accompany storms, the scattered nature
of the storms and progressive movement likely will limit
widespread higher rain amounts, but localized 2 inch amounts
could occur. Urban areas or poor drainage areas will be
susceptible to higher rain rates and localized flooding.

Smoke:

Smoke from wildfires to the north continues to impact the area today
within the ridge of high pressure with continued visibility/air
quality impacts. Some gradual improvement in visibility has
been occurring today with diurnal mixing, with more substantial
improvement suggested by the RRFS/HRRR through the day on Monday
as winds increase out of the south ahead of the cold front.

Rest of the week:

High pressure builds south behind the cold front providing cooler
and drier weather for mid-week. By late week into next weekend, mid-
level ridging is forecast to build eastward from the Rockies with
gradually warming temps. No strong signal for precipitation is
apparent late week with low predictability in placement of any
smaller scale shortwave troughs.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 717 PM CDT Sun Jul 19 2026

Smoke trends main issue through late tonight. Given steady SW
winds and smoke not as thick as Saturday, expect vsby 2-4 SM,
lowest over central WI. First chance of showers and storms arrives
over central/north-central WI on Monday morning. Expect these
storms to be on weakening trend, but brief IFR vsby could occur.
Remnants of these storms could reach eastern WI TAF sites late
morning, but with expected weakening, continue to only mention
showers, with no TS. Otherwise, MVFR vsby from smoke will slowly
improve by midday over central WI, then over eastern WI mid to
late afternoon. Lowest vsby will be 3-4SM.

Late afternoon, expect showers and storms to blossom over central/north-
central WI. Initially the coverage will be scattered, so mentioned
as a TEMPO. Toward 24z, showers and storms should become more
widespread in coverage, so have opted for prevailing groups for TS
at GRB/ATW after 23z, led in by a prob30 group after 21z. Most TS
will not make it to MTW until after end of TAF valid period. No
specifics put into the TS mention yet in terms of heavy rain,
gusty winds, hail, as these details can be added in later updates.
A direct hit from TS would result in sub VFR conditions, but not
enough confidence to include any notable reduction to vsby yet.

.KOSH...

Dry tonight with smoke trends main concern. Enough wind tonight
and less concentrated smoke to prohibit vsby lower than 3SM most
of the night, though brief IFR could occur overnight.

On Monday, the first cluster of showers and thunderstorms will
approach the site between 15z-18z Monday. No TS mentioned as
storms will be on the weakening trend, but even though weakening,
the showers could still produce brief gusty outflow winds from
the NW. Decent agreement that primary window for showers and
storms at Oshkosh will be after 22z, and especially after 00z.
Have put prob30 to lead into this time, starting at 21z, with a
prevailing group for TS at 23z. Similar to other eastern WI TAF
sites, did not include specifics with the TS mention yet in terms
of heavy rain, gusty winds, hail, as these details can be added in
later updates. A direct hit from TS would result in sub VFR
conditions, but not enough confidence to include any notable
reduction to vsby yet.

&&

.MARINE...
Issued at 225 PM 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 Advisory has been issued. A Beach Hazards Statement has
also been issued.

Wildfire smoke will also continue to impact Green Bay and Lake
Michigan through least Monday morning, dropping visibilities to
around 1NM at times. The Dense Marine Smoke Advisory continues
into tonight.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement from Monday morning through Tuesday
morning for WIZ022-040-050.
&&

$$

DISCUSSION.....JM
AVIATION.......JLA
MARINE.........JM

NWS GRB Office Area Forecast Discussion