373
FXUS63 KGRB 171910
AFDGRB

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

.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 /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1200 PM CDT Fri Jul 17 2026

Low pressure moving across Lake Superior will push a cold front
across the region late tonight. Southwest winds are shifting
the smoke reduced visibilities to the northeast across the
region and ahead of this front late this morning. As a result,
should see improving visibilities from southwest to northeast
this afternoon at all TAF sites. Otherwise, VFR fair weather
clouds are expected this afternoon.

There is a chance of showers and thunderstorms along the front
tonight, though chances will decrease through the night. Highest
chances (50%) will occur at RHI and will make minor timing changes
to the tempo group. Prob30s look good at AUW, CWA, GRB, and ATW
though made minor timing changes there too. Brief IFR flight
conditions are possible in thunderstorms.

With the frontal passage, winds will turn to the northwest with
gusts up to 20 mph possible. More fair weather clouds will likely
pop on Saturday morning.

Lastly, some guidance brings MVFR ceilings into far northern WI on
Saturday morning that could impact RHI. Left ceilings as scattered
for this issuance. Smoke will likely return into far northern WI
by late in the TAF period, but impacts will likely hold off until
after 18z at the terminals.

.KOSH...
Visibilities are improving over central WI late this morning and
expect this trend to continue east into KOSH this afternoon.
Therefore, smoke remains on track to clear out this afternoon,
likely between 18-21Z. However, thicker smoke is likely to move
back into the area on Saturday night and Sunday as flow turns back
to the north. Until the smoke clears, surface obs will continue
to show MVFR ceilings at times, however, these ceilings are tied
to smoke rather than clouds. Otherwise, VFR fair weather clouds
are forecast this afternoon.

A cold front will bring a very low chance (under 15%) of showers
early Saturday morning (08-12Z) and too low for a prob30 group.

S/SW winds of 6-13 kts are expected through much of the day
today. Overnight winds will shift to the NW behind a cold front
and may gust up to near 20 mph.

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

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...None.
MARINE...Dense Smoke Advisory until 7 PM CDT this evening for LMZ521-
     522-541>543.

&&

$$

DISCUSSION...JM
AVIATION...MPC

NWS GRB Office Area Forecast Discussion