278
FXUS63 KARX 051901
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
201 PM CDT Fri Sep 5 2025

.KEY MESSAGES...

- Isolated showers are possible this afternoon (10-20%) and
  Sunday afternoon (10-30%).

- Temperatures remain 10 to 15 degrees below normal through the
  weekend.

- Showers and storms are possible Monday night into Tuesday
  before temperatures warm through the end of the week.

&&

.DISCUSSION...
Issued at 200 PM CDT Fri Sep 5 2025

Showers Today and Saturday

A 500hPa shortwave trough has been moving southeastward out of the
Northern Plains within the longwave trough that has been situated
over the Great Lakes through the morning hours and has made its way
into the Upper Mississippi River Valley this afternoon. Forcing
associated with this feature combined with slightly steepened 850-
750hPa lapse rates should be enough for some isolated showers to
develop this afternoon (10-20%). The main factor against showers is
a lack of sufficient moisture across much of the area. Areas along
and north of I-94 appear to have a little bit more moisture to work
with based on RAP/HRRR soundings, so confidence in shower
development is highest in north-central Wisconsin. Breezy winds will
also continue through the afternoon given the tightened
pressure gradient associated with the aforementioned longwave
trough, generally at 20-30mph.

A similar, but more favorable, scenario for showers plays out on
Saturday as another shortwave trough drops southward into the Upper
Midwest. A slug of 850-700hPa moisture and 700hPa cold air advection
moves into the region along with the wave, saturating the 850-700hPa
layer while also steepening the lapse rates which should provide
enough moisture and instability for shower development by the
afternoon, continuing into the evening hours. Confidence is higher
in scattered showers Saturday afternoon as compared to today given
the more favorable conditions (10-30%). Breezy winds of 20-25mph are
expected again Saturday.

Below Normal Temperatures Continue

The below normal temperatures will continue through the weekend
with high temperatures in the upper 50s to low 60s and low
temperatures falling into the mid 30s to low 40s given 925hPa
temperatures of 6 to 12 degrees. In areas where the low
temperatures fall into the mid 30s, frost may become possible,
with the most favorable locations being those in north-central
Wisconsin where temperatures are expected to be coldest. Some
uncertainty regarding cloud cover during the overnights limits
confidence in frost development though. The 05.06z GEFS/ENS
means suggest clear to mostly clear skies over north-central
Wisconsin, promoting nocturnal cooling, while low level moisture
depicted in the deterministic guidance suggests there could be
cloudy skies during the nights, limiting nocturnal cooling. If
sky cover trends towards the clearer solution depicted by the
ensemble means, frost will become more of a concern this
weekend.

Showers and Storms Monday into Tuesday and Warming Temperatures

500hPa ridging over the western United States begins to build
eastward early next week, promoting increasing heights and warming
temperatures. A shortwave trough evident at 700hPa precedes the main
ridge axis Monday night into Tuesday, promoting strong 850hPa
southwesterly flow, strong warm air advection, and strong
moisture transport over the Upper Mississippi River Valley. The
combination of these parameters should lead to a favorable
environment for precipitation during this period. The 05.00z
LREF suggests only a 20-30% to exceed 0.5 inches, but this
probability has been trending upward over the past 24 hours, so
the total amount remains in question. The trough shifts eastward
by Wednesday allowing for the aforementioned ridge to build
into the central United States, promoting rising heights and
temperatures warming back into the 70s to end the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1150 AM CDT Fri Sep 5 2025

CIGS: mostly bkn VFR deck expected through the afternoon with short
term guidance favoring a scattering this evening. Can`t rule out
short periods of BKN here and there. Moving into Sat afternoon,
diurnal cu enhanced by an upper level shortwave suggest another
round of BKN cigs - but favoring VFR at this time.

VSBY/WX: a smattering of sprinkles possible this afternoon, but
chances generally <15%. Will not continue mention in the TAF
forecasts.

Sat afternoon looks a bit more favorable for scattered -SHRA with
afternoon instability and an upper level shortwave working together.
VCSH or PROB30 may be warranted after 18z Sat.

WINDS: daytime mixing will continue to keep it gusty for KRST and
KLSE through the afternoon - mostly low/mid 20 kts. They will settle
down with sundown. Could see more gusts Sat afternoon but RAP/HRRR
forecast soundings and weaker pressure gradient suggest they will be
less than today. West/northwest in direction through the period.

&&

.CLIMATE...
Issued at 200 PM CDT Fri Sep 5 2025

Record cool maximum temperatures and the current forecast.


 La Crosse, WI

Date           Record Cold High       Forecast High
-----           -----------            -----------
9/6              60F(1965)                63F

 Rochester, MN

Date           Record Cold High       Forecast High
-----           -----------            -----------
9/6              58F(1965)                59F

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Rieck
CLIMATE...Falkinham