740
FXUS63 KARX 022347
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
647 PM CDT Tue Sep 2 2025

.KEY MESSAGES...

- Showers and thunderstorms continue this afternoon, some of
  which could produce funnel clouds through the afternoon.
  Showers and storms are expected overnight (50-80%) with
  additional showers Wednesday afternoon (30-40%).

- Colder temperatures are expected for the end of the week with
  highs and lows 10 to 15 degrees below normal.

- Showers and possibly a storm return Thursday into Friday
  (60-80%).

&&

.DISCUSSION...
Issued at 208 PM CDT Tue Sep 2 2025

Showers and Storms Today into Wednesday

Showers and thunderstorms associated with a 500hPa shortwave
trough and surface MCV over northern Minnesota have been moving
southeastward across Minnesota through the morning hours and
have made their way into our area this afternoon. Confidence is
low regarding the evolution of these showers and storms as we
continue into the afternoon hours as the CAMs have been
struggling to handle their evolution. Several boundaries have
developed across portions of southeast Minnesota and northeast
Iowa, primarily associated with the outflow from the earlier
storms, which coincide with building MLCAPE values of 500-1000
J/kg through the afternoon. Highest confidence in showers and
storms is along these boundaries within the more convectively
favorable environment, but as the MCV moves through northern
Wisconsin, could see some additional shower development with
perhaps a rumble of thunder. With light winds through the
troposphere, effective shear is meager at best so any storms
that develop are not expected to become severe. However, funnel
clouds could develop from storms along the boundaries given NST
values greater than 1, steep 0-3km lapse rates, and low level
instability.

Higher confidence in the forecast comes this evening and
overnight as a cold front currently situated over northern
Minnesota into central South Dakota propagates southeastward
through the area. Convergence along the front along with skinny
instability profiles of 250-1000 J/kg should allow for shower
and storm development overnight into Wednesday morning. After
the front moves through the region Wednesday, cold air advection
behind the front will allow for steepening 0-3km lapse rates,
providing enough instability for additional shower development
by the late afternoon (30-40%).

Cooler Temperatures to End the Week

Behind the cold front, the  aforementioned cold air advection
will bring much cooler temperatures to the region, generally 10
to 15 degrees below normal. Given the below normal temperatures,
there is some concern for frost development towards northern
and central Wisconsin Wednesday night into Thursday morning.
The 02.13z NBM mean depicts low temperatures in the mid to upper
30s with the 10th percentile falling to just above freezing.
Dependent on the ultimate sky condition and low level wind
field, which are somewhat uncertain at the moment given the
upper trough remaining over the region, frost may become a
concern. Will need to monitor trends, but current probabilities
of frost development are low based on the 02.00z LREF (< 15%).

Showers and Storms Thursday into Friday

Another upper level shortwave will dive southward out of Canada
Thursday into Friday, supporting a surface low and associated
frontal boundaries. This will provide the next best time period
for notable precipitation development across the Upper
Mississippi River Valley (60-80%). Discrepancies regarding the
location of the low and the associated fronts is noted in the
02.00z GEFS/ENS/GEPS and their deterministic solutions which leads
to low confidence in the ultimate outcome.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 647 PM CDT Tue Sep 2 2025

Showers and occasional storms will be the primary aviation concern
across the region tonight and into the morning hours on Wednesday.
VFR conditions will begin the period for much of the local area,
however around 06z a surface cold front will approach the local area
bringing a round of showers and storms during the overnight hours.
Highest confidence for any TSRA impacts per some of the recent CAMs
would be along and east of the Mississippi River which may result in
periods of IFR vsby reductions. Cigs will drop to MVFR heights
during the overnight as well with the 02.18z HREF having high
probabilities (40-80%) for MVFR cigs through 16-18z Wednesday.
As diurnal mixing kicks in during the afternoon on Wednesday,
this will aid in increasing cigs to VFR but will also increase
winds to around 10-15 kts from the northwest with occasional
gusts to around 20 kts. A few showers will be possible late into
the TAF period around 21z to 00z in southeast MN. However,
exact confidence in how these will evolve remains low at this
time.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Naylor