207
FXUS63 KARX 181104
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
604 AM CDT Tue Aug 18 2026

.KEY MESSAGES...

- A few rounds of showers and storms today, but severe weather
  unlikely.

- Periodic shower and storm chances Thursday through Friday
  night, then likely drier and slightly cooler than normal.

&&

.DISCUSSION...
Issued at 1236 AM CDT Tue Aug 18 2026

A few rounds of showers and storms today

Potentially a few rounds of showers and storms today as some weak
shortwaves and MCSs embedded in northwest flow aloft ripple through
the region. Scattered upstream evening convection over portions of
Minnesota and the Dakotas was tied to a plume of modest instability
approaching 2000 J/kg, with a sharp instability gradient eastward
into our forecast area. Through daybreak, that diminishing plume of
instability will spill eastward with MUCAPE around 1000 J/kg or
less, supporting gradually weakening clusters of storms diving
east/southeast through the forecast area. Because of the rather weak
forcing, CAMs aren`t in the best agreement, but they lend support
for most of our area to be impacted by at least one such cluster
through the morning hours, with the greatest chances (50-60%)
generally near and west of the Mississippi River. No severe weather
expected with this round of elevated morning convection.

Lingering clouds after morning showers and storms will likely temper
our daytime warming, and the forecast has been trending a smidge
cooler for today`s highs. The main forecast question revolves around
how much we manage to destabilize ahead of potentially another round
of scattered storms this afternoon. This activity would seem to be
focused mainly south of I-90 as drier air will be encroaching from
the north, but CAMs are not in much agreement as it hinges on how
morning convection plays out. Better theta-e convergence will be
found south of I-90, and that is where the 00Z HRRR initiates late-
afternoon scattered storms. While deep layer near-unidirectional
shear magnitude will be respectable (50+ knots), weak forcing and
limited instability thanks to weak mid-level lapse rates should
inhibit severe potential locally. Forecast soundings show the deeper
(albeit skinny) CAPE profiles in our far south, suggesting that
would be where any healthier updrafts could conceivably manage to
develop, but it looks marginal at best. So, thinking a marginal SPC
risk is adequate for potentially an isolated wind threat late this
afternoon-evening.

Today does not have the look of a widespread soaking rainfall event,
given weak to modest moisture transport, limited warm cloud depths,
and progressive storm cluster motion. Looking like 0.25 to 0.5" on
average, with some higher pockets perhaps exceeding 1 inch.

Periodic rain chances Thursday and Friday, then generally drier

Under broad upper troughing, a drier airmass briefly takes hold for
Wednesday with embedded shortwave activity just clipping our far
southern forecast area. Weak moisture return gradually takes hold
Thursday into Friday, ushering in PWATs around 1.25". This will
allow for the return of periodic shower and storm chances as an
active northwest flow pattern takes hold aloft. Thursday night into
Friday brings the highest chances (50-70%).

This weekend and beyond becomes a little murkier of a forecast for
rain chances given diverging upper level flow patterns between
various guidance, but overall it looks fairly dry and slightly
cooler than normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 604 AM CDT Tue Aug 18 2026

VFR conditions are expected throughout much of the TAF period with
showers and storms being the primary TAF concern. Recent CAMs
highlight areas near I-94 for convective development so have
opted to maintain a prob30 for -tsra at KLSE through 00z. Strong
wind gusts may accompany any more robust storms. Otherwise,
winds will shift from southwesterly to westerly today with winds
around 5-10 kts before diminishing overnight.

&&

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

&&

$$

DISCUSSION...Kurz
AVIATION...Naylor