468
FXUS63 KARX 080554
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1254 AM CDT Tue Jul 8 2025

.KEY MESSAGES...

- Scattered showers-storms tonight into Tue morning.

- Widespread shower/storm chances Friday. Humid airmass will promote
locally heavy rain. Some strong storm risk.

&&

.DISCUSSION...
Issued at 130 PM CDT Mon Jul 7 2025

> REST OF THE AFTERNOON/EARLY EVENING: spotty convection south

A weakly convergent sfc boundary runs north-south across northeast
IA/southwest WI early this afternoon with perhaps a meso low in
there too. Ribbon of higher sfc Tds in that region with MLCAPES from
250-500 J/kg currently, progged in the RAP to climb to 1000 J/kg.
Not unsurprisingly, some convection has started to pop as a result
of this mix of weaker forcing and instability, and expect that to
persist for the rest of the afternoon/early evening. Some of the
CAMS capture this - but might be too spotty in coverage.


> TONIGHT-TUESDAY: shower/storm chances

Convection firing over the northern plains this afternoon, tied with
an upper level shortwave trough/sfc cool front, will track southeast
tonight...slipping over eastern WI by Tue afternoon. The
areas/bands of showers/storms should lose some areal coverage and
intensity as they move east tonight - losing out on the daytime
instability. More of the pcpn focus could center on the shortwave
moving across northern parts of the region and southward over IA
where an MCV and branch of the low level jet will play roles. Expect
pcpn chances for the local forecast area, but could be more
scattered in nature.

Moving into Tue afternoon, instability  builds post the departing
front/trough axis. A secondary sfc boundary may be sliding southeast
across the region while remnants of upper level energy continue to
pinwheel post the trough axis. RAP/HRRR soundings suggest the
atmosphere would become uncapped by mid afternoon, so even weak
forcing could be enough to spark isolated/scattered convection.
CAMS, however, aren`t that enthusiastic on these prospects. Lacking
clarity in the forcing mechanisms (are they there? where?) will opt
in with the model blend for the rain chances - for now.


> FRIDAY; humid with shower/storm chances. Locally heavy rain and
stronger storm potential

GEFS and EPS remain on track with slipping a bit of upper level
energy out of the southern rockies Thu, spinning it east/northeast
across the upper mississippi river valley Fri. On its heels, another
shortwave trough (a bit stronger) looks to drop out of western
Canada, making its way across the northern plains, swinging across
northern parts of the region Sat. The models favor keeping these
feature separate - but can`t completely rule out them merging as
they swing northeast in southern Canada.

Strong push of low level moisture ahead of the first bit of energy
will push PWs north of 2" and warm cloud depths from 4 to 4.5 kft.
Soupy and unstable. All this is ahead of the shortwave`s associated
cool front. Both of the models` suite of members produce QPF in the
Fri/Sat time frame, with expected differences in amounts/timing.
Shaping up to be the "most likely" period for widespread pcpn.
Depending on where/when the shortwave and cold front move in from
the west, the mix of instability/shear could promote stronger storms.
Something worth keeping an eye on. At the very least, the airmass
favors storms capable of locally heavy rain.

The shower/storm chances could linger through Sat, but could also be
clearing north/east of the local forecast area in the morning.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1234 AM CDT Tue Jul 8 2025

A line of storms has mostly dissipated and weakened across the
forecast area progressing east through southeast Minnesota and
northeast Iowa into western Wisconsin. Subsequent impacts will
be low chance (<20%) for scattered storms through today
concurrent with peak daytime heating. Have not included in
either TAF (KRST & KLSE) given the very low confidence but will
need to be accounted for in coming TAFs.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...JAR