413
FXUS63 KARX 182338
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
638 PM CDT Sat Jul 18 2026

.KEY MESSAGES...

- Air quality concerns return tonight through Sunday as
  northerly winds bring wildfire smoke back to the area.

- Monday continues to show promise for severe weather potential,
  but details remain uncertain.

- Cooler temperatures and mostly dry weather are expected
  Tuesday through the end of next week.

&&

.DISCUSSION...
Issued at 135 PM CDT Sat Jul 18 2026

Today - Sunday: Air Quality Concerns Return

Post-frontal northerly winds have already started to bring some more
smoke down from the Canadian wildfires into the Upper Mississippi
River Valley, with some of it already mixing down to the surface
creating slight visibility reductions. The concentration of near
surface smoke is expected to increase later this evening and
especially overnight, primarily for our Wisconsin counties and
portions of SE Minnesota. Forecasted smoke does not look to be
nearly as dense as it was earlier in the week but visibility
reductions are expected with Air Quality Alerts already out for the
entire state of Wisconsin through noon Monday. All the smoke
that gets pushed south tonight will then start to make its way
back north as surface winds shift back to the south/southeast,
meaning the smoke is going to be sticking around in some
capacity through much of the day on Sunday. Concentrations are
expected to get lighter through the day Sunday as the nighttime
inversion breaks and allows for diurnal mixing. With the smoke
partially limiting daytime heating tomorrow, high temperatures
will be moderated in the low to mid 80s.

Monday - Monday Night: Strong to Severe Storm Potential

As the upper ridge across much of the central CONUS starts to
flatten out and retrograde slightly to the west, this is putting the
Upper Midwest in more progressive northwesterly flow aloft. Late
Sunday into Monday, an upper trough is expected to strengthen across
the Canadian Plains, dropping southeast into the Upper Midwest and
Great Lakes. At the base of this trough, a 500 mb jet max will
overspread the Upper Midwest through the day on Monday. At the
surface, a low pressure center will be located north of the Canadian
border, likely in Western Ontario by 12Z Monday. A trailing cold
front over northern Minnesota and the Dakotas is expected to slide
southeast into the region by the evening, providing ample lift at
the surface. A very moist and potentially extremely unstable airmass
is forecast to develop through the afternoon with forecast soundings
showing 3000-4000+ J/kg of SBCAPE with between 50-70 kts of
effective bulk shear. All hazards are possible with the initial
supercellular growth along the cold front but a wind threat will
be favored overall as forcing along the front and the overall
progressive nature of the system will likely result in quick
upscale growth into a bowing linear feature. Forecast DCAPE
values are also expected to exceed 1000 J/kg, favoring
downburst wind potential. These storms will produce a quick bout
of heavy rain given forecast pWats between 1.5-1.8 inches but
with the progressive nature of the storms, a flash flood threat
is not currently anticipated. One of the main limiting factors
in confidence for the event as a whole is the likelihood of an
early Monday morning MCS moving through the region. If this can
move out as quickly as many models are suggesting in the 00/12Z
suites, the thermodynamic and kinematic profiles would suggest a
medium-high chance of severe storms across the area Monday
afternoon and evening. If this MCS moves in slower than
anticipated and/or lingers longer into the morning, this could
limit the recovery for the afternoon/evening activity,
potentially limiting their intensity. Details on timing,
especially with this morning activity will be crucial to how
Monday`s event ultimately plays out so further refining is to be
expected over the next 36-48 hours, especially as hi-
resolution guidance and CAMs start to come into range.

Tuesday - End of the Week: Cooler Temperatures and Mostly Dry

Once the cold front passes and the storms clear out late Monday
night, there should be a noticeable difference across the area with
an overall much cooler airmass expected for mid next week.
Temperatures Tuesday and Wednesday will finally drop below average
into the upper 70s to low 80s with dry conditions expected as a weak
surface high pressure moves in behind the front. While a quick
moving disturbance may bring some low rain chances to the area by
late week, expect generally dry conditions and near normal
temperatures to round out the next work week.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 638 PM CDT Sat Jul 18 2026

The main aviation impact over the next 24 hours will be wildfire
smoke currently moving southward from northern Wisconsin given
light northerly winds. MVFR visibilities may be realized within
the heaviest smoke, primarily across north-central Wisconsin
where many sites are already reporting visibility around 2-4SM,
though the 18.18z REFS does suggest a 10-20% chance for less
than 6SM for areas across western and southwestern Wisconsin.
Surface winds will be variable overnight as they veer to the
south for Sunday but remain light, so smoke is expected to
linger through the TAF period after it arrives.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...Barendse
AVIATION...Falkinham