697
FXUS63 KGRB 181118
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
618 AM CDT Sat Jul 18 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Another plumb of wildfire smoke is expected to spread over the
  region from north to south this afternoon. Smoke will then
  likely cycle around the region through the weekend. Degraded air
  quality and visibility are expected at times.

- A round of thunderstorms is likely (60-80%) to impact the region
  Monday into Monday night. There is a level 2 out of 5 severe
  thunderstorms risk Monday.

&&

.DISCUSSION...
Issued at 220 AM CDT Sat Jul 18 2026

Precip/Thunderstorm Chances...A cold front moving into far northwest
WI early this morning will continue to progress south east through the
morning. Along the front a few isolated showers or weak storms are
possible (20-30%) through about 7AM this morning. Once the front
clears the region upper riding will start to build in keeping this
weekend dry.

Monday remains the main focus for thunderstorm activity as an upper
level vorticity max and seasonally strong jet streak are progged to
move across the state. At the surface southerly winds will deliver a
plumb of upper 60s to low 70s dew points which paired with steep mid-
level lapse rates associated with an elevated mix layer will result
in strong destabilization. The combination of favorable
thermodynamics and kinematics will create a parameter space
supportive of possible higher end severe storms Monday. However,
storm scale details such as timing, storm mode, and convective
evolution remain uncertain. A few key features to watch will be
how any morning convection modifies the environment and how much
instability is able to recover. There will also likely be some
elevated wildfire smoke over the region that may also hamper
instability to some extent. Lastly, the degree of capping
associated with the EML will be key in determining how much
instability can build through the day ahead of the surface front.
Think the high end scenario would be a round of elevated storms
during the early morning capable of producing marginally severe
hail and damaging winds followed by a lull in storm active through
the late morning and afternoon then a period of semi discrete
super cells with all severe hazards possible. Quick upscale growth
along the progressive front may then lead to the development of a
QLCS with bowing segments producing swaths of damaging winds
Monday evening. A lower end scenario is that morning convection
lingers into the afternoon shunting the stronger instability to
the south and increasing capping resulting is much less impressive
severe potential. As CAMs come into range over the next 24-48
hours some of these details will come more into focus, but how
exactly storms will play out may not be clear until Monday
morning.

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

Smoke Trends...Relief from the smoke will be rather short-lived as
winds shifting back to the northwest today allowing another plumb
of smoke to cycle over the region this afternoon through Sunday.
However, HRRR and RRFS surface smoke fields show this round of
smoke being less intense than this past Wednesday/Thursday. Still
impacts to air quality and visibility are expected today and
Sunday. 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.

Temperature Trends...Seasonably warm temperatures are expected this
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 12Z TAF Issuance
Issued at 618 AM CDT Sat Jul 18 2026

With the frontal passage through the region early this morning winds
have turned to the northwest with gusts to around 20 kts. Expect
breezy northerly winds to continue to the TAF period. Fair weather
clouds will likely pop on this morning, however, incoming smoke may
limit the extent of the cloud cover today. Smoke will also impact
vsbys today as it spreads from north to south. For now have vsbys
gradually trending from low end VFR to MVFR beginning late this
morning through the afternoon. This plumb of smoke does not look
quite as intense as this past Wednesday and Thursday, however, can`t
rule out periods of IFR vsbys, especially across northern WI late
this afternoon and evening. Smoke will likely stick around for much
of Sunday as well.

.KOSH...

VFR conditions are expected to prevail at OSH this morning. In the
wake of a cold front that passes overnight winds have shifted to the
northwest this morning with gusts up to 20kts possible through the
morning. During the day winds will gradually shift around to the
north and eventually northeast by this evening.

Main impact to aviation at OSH today will the another round of
wildfire smoke that will spread into OSH early this afternoon. By
19Z smoke may be thick enough to start restricting vsbys to under
5SM. These MVFR vsbys will likely then persist through the afternoon
and evening. This round of smoke does not appear quite as dense as
what OSH saw on Thursday, however, vsbys as low as 2-3SM seem
possible tonight. Smoke will likely stick around for much of Sunday
as well.

&&

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

&&

$$

DISCUSSION.....GK
AVIATION.......GK