979
FXUS63 KGRB 180358
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1058 PM CDT Fri Jul 17 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Some improvement from the smoky conditions from the west this
  afternoon and tonight although additional smoke will spread
  south across the area Saturday and Sunday with potential
  visibility and air quality impacts.

- There is a 40-70% chance for storms across northern
  Wisconsin, especially between 8 pm and midnight, with a low
  chance (less than 15%) for a severe storm. Storm chances
  decrease southward.

- Additional rounds of storms expected (60-80% chance) Sunday
  night through Monday night. There is a level 2 of 5 risk of
  severe storms on Monday.

&&

.DISCUSSION...
Issued at 210 PM CDT Fri Jul 17 2026

Thunderstorm potential:

This afternoon-tonight: There is a level 1 of 5 risk of severe
storms across northern Wisconsin, with the primary focus along a
cold front that will swing south this evening and tonight. The
highest thunderstorm potential will be across northern
Wisconsin, especially from 8 pm to midnight, with storm chances
decreasing with southward extent away from the stronger mid-
level flow, weaker forcing, and diminishing instability with
loss of daytime heating. Overall, locally damaging winds and
hail will be the primary threats with any stronger, more
organized updrafts.

Isolated showers or a storm cannot be ruled out ahead of the
cold front through this afternoon, but forcing for ascent will
be weak, so expect little organization.

Sunday night-Monday: A potentially more impactful severe weather
event may evolve during this time with a level 2 of 5 severe
weather risk in place from SPC. Global ensemble mean 500 mb
flow exceeds the 95% percentile relative to climo with
precipitable water values near the 90th percentile. This will
support a favorable thermodynamic and kinematic environment
ahead of an approaching cold front for severe storms. However,
at this time range, convective evolution is unclear, including
potential impacts of smoke on destabilization and on early day
warm-advection induced precipitation on the later day
environment. This period will bear watching through the weekend
as trends become more clear, though.

Behind this front, drier weather is expected for mid-week as high
pressure builds in with gusty northerly winds on Tuesday.

Smoke:

Some relief from the smoke is expected into tonight before winds
shift back to the north late tonight into Saturday. Both
HRRR/RRFS smoke models suggest increasing smoke later Saturday
and persisting within the surface ridge axis on Sunday. This
smoke will likely have additional impacts to visibility and air
quality. With northwest flow aloft amplifying next week,
additional bouts of smoke may impact the area over the next
week, dependent on fire behavior to the north and wind direction.

Temperatures:

Seasonably warm temperatures are expected through the weekend under
surface high pressure, but with less humid conditions. Stronger
cold advection will occur behind the frontal passage early next
week, with near to below average temps then favored through
late next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1058 PM CDT Fri Jul 17 2026

Low pressure moving across Lake Superior will push a cold front
across the region overnight. Isolated showers and thunderstorms
are expected to push into the area as the front drops south,
though chances will decrease through the night as instability
wanes. Looks like the thunder will just miss AUW/CWA, so have
removed the thunder and went with a TEMPO group for showers. Also
will continue with TEMPO groups for showers at GRB/ATW/MTW/OSH as
instability will be waning overnight. Brief IFR flight conditions
and gusty winds are possible in any storm.

With the frontal passage, winds will turn to the northwest with
gusts to around 20 kts possible. More fair weather clouds will
likely pop on Saturday morning into the afternoon. Some MVFR
ceilings are possible in far northern WI on Saturday morning that
could impact RHI. Left ceilings as scattered for this issuance.
Smoke will likely return into the region on Saturday, spreading
from north to south. However, concentrations are not looking as
intense, so will keep VSBYs in the 3-6SM range for now.

.KOSH...

VFR conditions expected the rest of the night. A cold front will
bring a very low chance (under 20%) of showers early Saturday
morning (07-11Z). Will continue with a PROB30 group for these
shower chances, but impacts to aviation look to be little to none.
SW winds will shift to the NW as the front moves through
overnight, with NW wind gusts to around 20 kts. Another batch of
smoke is forecast to move back into the area on Saturday
afternoon/evening and could stick around at times into Sunday.
This batch does not look as intense, so will keep VFR VSBYs but if
the thicker smoke gets a little further south than anticipated,
MVFR VSBYs would occur.

Looking ahead, there is an increasing chance for one or more
rounds of thunderstorms to move across the Fox Valley on Monday.

&&

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

&&

$$

DISCUSSION.....JM
AVIATION.......Bersch

NWS GRB Office Area Forecast Discussion