140
FXUS63 KARX 030527
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1227 AM CDT Wed Sep 3 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1208 AM CDT Wed Sep 3 2025

More scattered nature to ongoing storms observed at 04.06Z TAF
issuance compared to previous forecasts lowers overall
confidence in potential aviation impacts through the early
morning hours. Radar reflectivity depicts highest confidence
initially along the northeastern half of the forecast area from
west-central into central Wisconsin. Some unstable air allowing
storms are quickly fill in after formation, persisting thunder
threat. Expect frontal boundary to progress east-southeast
through the forecast area over the next few hours.

While frontal boundary pushes south of the local forecast area
through the morning, isolated storm threat could persist through
the evening as bouts of strong cold air advection causes transient
instability. While not widespread, current area of concern primarily
from southeast Minnesota through central Wisconsin. Widespread flight
impacts will be low MVFR to higher IFR ceilings from colder air saturating
lower levels. Expect widespread impacts to wane into tonight.

Cold air advection also causes increased northwest winds area
wide this morning through the evening.
Subsequent locally impacts expected overnight Thursday into
Friday morning with additional storm chances. Ceiling and strong
wind impacts could be felt through Friday due to more incoming
cold air.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...JAR