629
FXUS63 KARX 091119
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
619 AM CDT Sun Aug 9 2026

.KEY MESSAGES...

- Showers and storms likely (70-90% chance) this morning and
  early afternoon with the risk for some storms to become strong
  to severe, mainly south of I-90. Damaging wind gusts and
  locally heavy rainfall will be the primary threats with these
  storms.

- Additional storm chances Monday through Wednesday with some
  severe potential, however confidence in details remains low at
  this time.

- Seasonable temperatures through mid-week with highs in the
  upper 70s to middle 80s.

&&

.DISCUSSION...
Issued at 1152 PM CDT Sat Aug 8 2026

This Morning - Early Afternoon: Storms Likely, Some Strong to Severe

Initial forecast concerns this morning will feature likely storm
development as a 700mb shortwave moves through the Dakotas and into
the Upper Mississippi Valley. As this occurs, increasing warm air
advection and instability aloft will allow for a profound
instability gradient to setup across portions of the region. The
overall evolution manifests as discrete convection develops
west of the local area and progresses eastward during the
overnight and early morning hours. As this occurs, cold pools
with widespread discrete convection associated with the wave
will likely result in upscale growth with much of the CAMs
agreeing on pushing an MCS/MCV through the region with some
differences on exact timing but generally during the mid-morning
hours.

Overall, the main question during this period will be exactly
how much storms maintain as they move through the local area
since they will be pushing into a lower instability environment,
especially near the Mississippi River. The primary threat with
these storms would be damaging winds with the organized cold
pools and favorably oriented 0-3km shear vector. If a more
coherent MCV with embedded bowing structures can manifest (as
shown in the very recent 09.02z HRRR and 09.00z RRFS), would not
be shocked to see some gusts approaching 70 mph. An embedded
tornado cannot be fully ruled out with this given the
aforementioned 0-3km shear vector, however fairly respectable
capping present over the region would make this fairly unlikely.
This complex would generally be progressive in nature with much
of the CAMs generally having it exiting east of the local area
by early afternoon.

This Evening - Overnight: Slight Chance for Redeveloping Storms

Additional storm development later into the evening will heavily
hinge on how quickly convection during the morning and early
afternoon pushes through the region. Based on the current state of
the CAMs, convection later into the evening would seem less
favorable as the cold pool from this MCS would likely push the
instability gradient further south of the area. This being
said, if we can recover instability quick enough and convect by
evening, the environment would favor some multi-cellular
clusters with embedded supercells. In this scenario, large hail,
damaging wind gusts and locally heavy rainfall would be the
primary threats with continued development along the instability
gradient. Again, need to emphasize though that this is heavily
contingent on if we can recover any instability back into the
region in light of the morning and early afternoon convection.

Monday - Wednesday: Additional Storm Chances, Severe Storms and
Locally Heavy Rainfall Possible

As we head into the start of the work week, persistent zonal to
northwesterly flow will allow occasional shortwave
perturbations to move through the region. Consequently,
expecting additional chances for showers and storms. However,
much of this will be contingent on how storms for previous days
modify the instability gradient which will be the primary focus
for where storms form. Deterministic guidance (GFS/NAM/EC)
generally wants to highlight an additional shortwave
perturbation that moves through the region later Monday evening
and into the overnight. With fairly steep mid-level lapse rates
and some stronger flow aloft, wouldn`t be surprised if initial
development could trend supercellular before organizing cold
pools would trend towards a damaging wind threat. The trouble
with this again is where storms form will be contingent on where
the instability gradient is during this timeframe, which could
very likely remain south of the local area.

Heading into Tuesday and Wednesday, the aforementioned zonal to
northwesterly flow will persist over the local area. Consequently,
shower and storm chances (15-30% in the recent NBM) will remain
across the local area, however exact details at this point remain
largely uncertain due to evolution of how earlier days storms may
manifest. In any case, will need to watch for if repeated rounds of
storms may track over the same locations through mid-week as
precipitable waters remaining around 1.5-2" and deep warm cloud
depths would suggest storms from today through mid-week will likely
be efficient rainfall producers. Consequently, flooding concerns
would increase if multiple rounds of storms occur over the same
locations through mid-week.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 618 AM CDT Sun Aug 9 2026

A large cluster of storms currently stretching from South Central
Minnesota down into Central Iowa is starting to track east towards
the local region. These storms will impact the terminals over the
coming hours with transient MVFR CIGs and MVFR/IFR visibilities from
heavy rainfall. These storms should push off to the east through the
morning and into the earlier afternoon, leaving VFR conditions in
their wake. Another round of storms is possible this evening (a low
confidence scenario that will depend on the timing of the departure
of the morning storms and how quickly the atmosphere can recover)
across NE Iowa and SW Wisconsin but this should remain south of the
terminals. Southerly winds will prevail through the day with speeds
generally at or below 10 kts, becoming light and variable overnight.
This will allow for patchy fog development overnight across much of
the region. Low stratus is also expected to build in for areas along
and east of the Mississippi River with CIGs dropping into the
MVFR/IFR range.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...Barendse