964
FXUS63 KARX 032338
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
638 PM CDT Wed Sep 3 2025

.KEY MESSAGES...

- Isolated to scattered showers are possible this afternoon
  (10-30%). Frost is possible north of I-94 tonight (40-60%).
  A Frost Advisory has been issued.

- A quick hitting system moves through the region Thursday
  night, bringing rain and perhaps a rumble of thunder (60-90%).

- Temperatures remain cool through the weekend before a warming
  trend next week.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Sep 3 2025

Today and Tonight

Isolated to scattered showers are expected late this afternoon
into the evening associated with steepening lapse rates in the
850-700hPa layer via cold air advection (10-30%). Any showers
that develop will be light.

The abnormally cold airmass sinking into the Upper Midwest this
afternoon will drop temperatures to below normal values through
the end of the week. Tonight appears to be the coldest, as the
03.13z NBM depicts low temperatures of 35 to 40 degrees over the
region, lowest along and north of I-94. Clouds continue to
throw a wrench into the mix though, as lingering 850hPa moisture
is shown in RAP/HRRR soundings, making the ultimate low
temperature tricky to forecast. Lingering stronger low level
winds via the tightened pressure gradient associated with
departing low pressure over the Great Lakes could also hinder
frost development by decreasing condensation/deposition.
However, the favorable temperatures and early season timeframe
does lead to more concern of impacts from frost. Overall, a
marginal set-up for frost development is expected overnight,
hinging on several factors that need to come together correctly.
Provided skies clear and winds diminish overnight, confidence
is high that frost will develop.

Quick Hitting system Thursday night into Friday

Model guidance is in much better agreement regarding a 500hPa
shortwave trough diving south out of Canada Thursday,
propagating through our northwest flow aloft. Forcing associated
with this feature provides substantial support for deepening
throughout the troposphere and surface cyclogenesis. The surface
low and associated frontal system propagate eastward through
the Upper Mississippi River Valley Thursday night. Ahead of the
surface features, seasonable PWATs around 1 inch will coincide
with strong moisture convergence focused across the region.
Conditions appear more than suitable for rain during this
period, but less confident in storms given meager instability
and the overnight time period as MUCAPE values only climb to 250
J/kg, but a rumble of thunder can`t be ruled out. Given the
progressive nature of this system and the seasonable moisture,
precipitation amounts should generally be on the lower end with
the 03.13z NBM suggesting a 30-70% probability of 24 hour totals
greater than 0.25 inches. Towards north-central Wisconsin,
along and north of I-94, where the greatest convergent signal of
the moisture transport is currently expected to reside,
conditions are more favorable for higher amounts though,
generally 20-50% for greater than 0.5 inches.

Increasing Temperatures Next Week

The cooler temperatures will continue through the weekend under
the longwave trough situated over the Upper Great Lakes. After
one last shortwave pivots through the longwave pattern Saturday
afternoon, possibly bringing additional showers to the area
(30-50% in the 03.00z LREF), ridging builds into the Upper
Midwest. Under the rising heights and southerly flow beginning
to take back over, temperatures are expected to increase into
the 70s for much of the area.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 638 PM CDT Wed Sep 3 2025

VFR conditions are expected throughout the TAF period with a few
showers moving into the local area over the next couple of hours,
which bring a low chance for MVFR vsby reductions (20-40% chance).
Otherwise, winds will diminish to around 5 kts overnight from the
northwest before shifting westerly during the afternoon and
increasing to 10-12 kts with occasional gusts to 20 kts. While high
pressure is currently situated west of the local area tonight,
valley fog appears very unlikely (under 10% chance) at KLSE given
the strong winds just off the surface.

&&

.CLIMATE...
Issued at 211 PM CDT Wed Sep 3 2025

There still appears to be some chance at setting a record cool
maximum temperature on Friday (Sep 5) based on the current
forecast.

 La Crosse, WI

Date           Record Cold High       Forecast High
-----           -----------            -----------
9/4              60F(2008)                66F
9/5              59F(1896)                62F
9/6              60F(1965)                64F

 Rochester, MN

Date           Record Cold High       Forecast High
-----           -----------            -----------
9/4              60F(1994)                62F
9/5              59F(1956)                59F
9/6              58F(1965)                61F

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Frost Advisory from 2 AM to 8 AM CDT Thursday for WIZ017-029.
MN...None.
IA...None.

&&

$$

DISCUSSION...Falkinham
AVIATION...Naylor
CLIMATE...Falkinham