210
FXUS63 KARX 272346
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
646 PM CDT Wed Aug 27 2025

.KEY MESSAGES...

- Showers and storms are expected this afternoon and evening
  primarily across southeast Minnesota, northeast Iowa,
  southwest Wisconsin (30-60%) and again overnight primarily
  across Wisconsin (30-50%).

- Below normal temperatures are expected Thursday night into
  Friday morning, primarily across north-central Wisconsin.

- Uncertainty surrounding the possibility of showers and storms
  this weekend.

&&

.DISCUSSION...
Issued at 152 PM CDT Wed Aug 27 2025

Showers and Storms this Afternoon and Overnight

Across portions of southeast Minnesota, northeast Iowa, and
into southwest Wisconsin, showers are expected to redevelop this
afternoon into the overnight hours on the nose of 850hPa
moisture transport and warm air advection coincident with
forcing associated with a 500hPa shortwave trough pivoting
through the Great Lakes region (30-60%). Some rumbles of thunder
are possible with these showers during the afternoon hours
given MLCAPE values increasing to 500-1000 J/kg associated with
the moistening low levels, primarily over southeast Minnesota
where the greatest instability should develop. Given weak
effective shear of 25kts, not expecting organized storm
development with lighting and heavy rain the primary threats.

As the 500hPa shortwave trough pivots through the Upper Great
Lakes region this evening into Thursday, a surface cold front
will sink southward through Wisconsin, which will be the focus
of additional shower and storm development overnight. Forcing
associated with these features via 900-800hPa frontogenesis and
QG ascent are strongest across northern and eastern Wisconsin.
This suggests the highest probabilities for precipitation will
reside largely to the north and east of our area. However,
portions of north-central to central Wisconsin still have a
30-50% probability of precipitation as the front moves
southward. Elevated instability should remain present overnight
ahead of the front with MUCAPE values of 500-1000 J/kg noted in
model soundings, which would promote some thunder and lightning.
The strongest shear lies behind the front, so again not
expecting any sort of organized convection.

The front stalls across southern Wisconsin into northeast Iowa
by Thursday afternoon. Weak convergence along this boundary
appears to be the catalyst of additional shower development
Thursday afternoon (10-15%), but where showers develop will be
largely dependent on where the frontal boundary stalls.

Below Normal Temperatures Thursday Night into Friday Morning

Cold air advection behind the surface cold front moving
southward tonight will bring unseasonably cool low temperatures
back to the region Thursday night into Friday morning,
specifically across Wisconsin. 70-80% of the members in the
27.00z EFI depict low temperatures below the model climatology
indicative of these abnormal temperatures although the lack of a
shift-of-tails suggests low temperatures are unlikely to be
records. There is some uncertainty in how cold temperatures will
get Thursday night dependent on how clear the skies are, but
given the dry air behind the front, expecting skies to be mostly
clear. As such, temperatures towards the 25th percentile of the
model guidance seem reasonable. This results in low
temperatures in the low 40s towards north- central Wisconsin and
the low 50s towards northeast Iowa, generally 5-10 degrees
below normal for those in Wisconsin.

Shower and Storm Potential This Weekend

Quite a bit of uncertainty regarding the evolution of the
synoptic pattern and thus the surface conditions this weekend.
500hPa longwave ridging across the western United States slowly
builds eastward Friday as a shortwave trough promotes low-level
cyclogenesis over the Northern Plains. Where this cyclogenesis
occurs though remains in question and will lead to the ultimate
impacts we see across our area. The 27.00z GEFS suggests a much
more eastward solution with lower heights developing over
eastern South Dakota whereas the 27.00z EPS/GEPS develop the
lower heights over western South Dakota. With the more eastward
solution, probabilities of showers/storms across southeast
Minnesota and northeast Iowa (currently 15-20%) will increase
whereas the further westward solution will keep the higher
probabilities across central and western Minnesota.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 639 PM CDT Wed Aug 27 2025

A band of scattered MVFR showers and storms over SE Minnesota
and NE Iowa slowly shifts ESE and weakens prior to 06Z while a
secondary band of MVFR showers grazes areas north of an EAU to
ISW line during the same period. IFR to LIFR fog develops north
of an AEL to PVB line after 08Z and lingers through the mid
morning before lifting/scattering prior to 15Z. Light SSW winds
tonight veer to the NE for the day on Thursday at 5-10 kts.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Skow