066
FXUS63 KARX 012329
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
629 PM CDT Tue Jul 1 2025

.KEY MESSAGES...

- Smattering of storm chances Wed-Thu. A few stronger storms but the
threat for organized severe weather currently looks low.

- Steamy start to the holiday weekend with heat indices topping out
in the mid to upper 90s for the 4th. Cooler end with Sunday highs in
the upper 70s/lower 80s.

- Highest rain threat overnight Fri into Sat. Smaller chances for
storms Fri afternoon, but more uncertain.

&&

.DISCUSSION...
Issued at 100 PM CDT Tue Jul 1 2025

> WED-THU: Scattered storm chances. A few strong storms possible.

Convection expected to spark over the northern plains later tonight,
in response to ripples in the 500 mb flow along with nose of the 850
mb jet/moisture transport. These shower/storm clusters should
experience a decrease in coverage/intensity as they move southeast
Wed morning. However, these now convectively enhanced bits of upper
level energy will stay intact, spinning across the local area for
the afternoon/early evening. The summery airmass paints 1500-2500
J/kg of SBCAPE for the afternoon with much/if not all low level
capping eroding by mid afternoon. Roughly 35-40 kts of 0-6km shear
via the NAM/GFS could/would add support to convective updrafts and
sustainability-development. Enough there for a stronger storm
potential. More uncertainty on if there would be a severe risk.

It`s not clear where the upper level features will be by the
afternoon, and potentially any related sfc/outflow boundaries.
Expectation is for storms to pop in relation to the upper level
forcing and increasing instability, tracking southeast across parts
of the area. CAMS don`t indicate much areal coverage at this time.

The low level jet looks to reassert itself into northwest IA Wed
night, with another cluster of convection firing there - moving
southeast during the night.

For Thursday, a warm front is likely to be wavering across central
MN into central WI with more bits of convectively enhanced shortwave
energy dropping over the plains ridge. More scattered convection
should spark. Deterministic runs of the GFS/NAM/EC keep most of this
along/north of the warm front - roughly north of I-90. Again, fair
amount of uncertainty as various small scale interactions will
impact where storms develop/move. Also, not a lot of areal coverage
in the QPF footprint. Lack of deep layer shear could/would be a
limiting factor to storm development/sustainability.


> 4th OF JULY WEEKEND: steamy for the 4th. Showers, storms likely
Fri night and Sat.

With the upper level ridge shifting from the northern plains to
across the upper mississippi river valley Fri, a stronger southerly
fetch sets up. Sfc dewpoints on the climb, likely reaching/pushing
past 70 degrees. Increasing moisture transport with PWs upwards of 1
3/4". +1 to +2 in NAEFS and EC PW anomalies.

Going to be humid for the 4th as a result, but with highs currently
expected to top out around 90, heat indices will peak in the mid to
upper 90s. Very uncomfortable, but not quite heat advisory. Still,
with it being a holiday and lots of outdoor activities, a lot of
care should be taken to protect yourself, family and friends from
the heat.

The heat/humidly portends to an increasingly unstable airmass - the
grand ensemble lays out 2500-3000 J/kg of MUCAPE for Fri afternoon.
However, not much wind shear to compliment the instability. There
will be a low level cap to contend with too, which might not erode
until late in the day. Whether general airmass storms could kick off
is uncertain.

GEFS and EPS still on track to lift a shortwave trough out of the
southern rockies Friday, across the plains and then over parts of
the upper mississippi river valley overnight Fri/Sat. GEFS is
stronger overall with the feature. All have a related sfc cold
front, but some small differences in timing/location. The upshot is
a more expansive area of pcpn relating the shortwave and deeper
forcing with the shortwave and north of it`s associated sfc low.
Convection would still fire along the front, but coverage is more
questionable. Current timing places the higher rain threat overnight
Fri through Sat. That said, doesn`t look like a "washout" for Sat.

For Sunday,  most of the ensemble members layout a westward hanging
sfc trough that could be the focus for continue rain generation.
Where this would track is uncertain with not much agreement between
the GEFS and EC. Could be mostly dry, could have persistent
shower/storm chances.

Overall, steamy start to the holiday weekend and a cooler end.
Highest rain chances late Friday night into Sat.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 609 PM CDT Tue Jul 1 2025

Light winds overnight mostly remain out of the west potentially
varying southwest. Scattered cumulus builds again Wednesday.
VFR expected area wide through the 02.00Z TAF period. Potential
for MVFR near 03.06Z primarily in central Wisconsin. Fog
potential along the Wisconsin River Valley (KOVS) early Thursday
morning.

&&

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

&&

$$

DISCUSSION...Ferguson
AVIATION...JAR