075
FXUS63 KARX 221748
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1248 PM CDT Tue Apr 22 2025

.KEY MESSAGES...

- Periodic rain chances, with occasional thunder, through the week.
Additional rainfall through Thu night roughly from 1/2 to 1". A few
stronger storms possible with small hail threat.

- Need a dry day? Saturday continues to look like that day -
consensus in all the long term guidance.

&&

.DISCUSSION...
Issued at 215 AM CDT Tue Apr 22 2025

OVERVIEW: no big changes in the long term guidance with quick moving
zonal flow a loft, some height rises, and a carousel of shortwave
troughs (rain chances) with one promising period of ridging (dry!).
Pretty messy with a lot of weather elements at play.

> THiS MORNING: upper level shortwave trough is lifting northeast
across the region early this morning (evidenced in current
watervapor satellite imagery). Sfc boundary/warm front reflected at
the sfc with Low level warming preceding it. Broken convection has
developed from the forcing, mostly just showers along the northward
extent. To the south, specially far southern MN and IA, the low
level jet was nosing into central/northeast IA, providing an
additional boost to the convection while also tapping into a little
elevated instability. More storms in this area.

Latest CAMS hold most of the shower/storms to I-90 southward early
this morning, kicking east/southeast by 15z, following the weakening
low level jet and bit of upper level energy. Northward, the same
CAMS lifts the showers into northern/northeast WI before the noon
hour.

> REST OF TODAY-WED: in the north, the RAP suggests a low level
boundary will run from northwest WI to the southeast with some
potential for a bit of elevated instability at the top of the near
sfc stable layer. Despite the upper level forcing shifting
northward, there might be enough lift here for a smattering of
showers. Will hold low end chances (20%) in the north for he
afternoon (north of I-94).

In the south, the sfc boundary is set to settle across IA into
southern WI/northern IL. A better pool of instability builds south of
the front, but also looks capped from the low level warming. The low
level moisture transport sets up parallel to the front. Expectation
is for more convection to kick off around the front this afternoon.
While the deeper shear lies to the north, enough there to aid around
1000-1500 J/kg of MUCAPE for some stronger storms, perhaps a few
severe. Hail would be the main concern. Positioning the front is
obviously the biggest factor, and short term model trends all favor
holding that south of the forecast area.

Tonight, that sfc front is mostly stationary and the low level jet
will come into play (again), progged to nose into/across it by late
evening. A line of convection should fire along/north of the front.

Working farther into the overnight/toward daybreak Wed the HRRR/RAP
lift that front a bit northward and key in on an elevated region of
Fgen just north of it. Low level moisture transport surges across
it, along with 1000 J/kg of MUCAPE. Convective focus could turn to
this region (NE IA/SW WI)- and the latest RAP/HRRR suggest it will.

The rest of Wednesday will continue to see showers and storms
develop in the proximity and south of the front with the bulk of the
guidance holding the higher rain chances south of I-90. Bits of
shortwave energy set to shuffle in from the southwest Wed night, and
will continue more shower/storm chances.

Any strong/severe threat during this time? While the setup favors
keeping some low level warming/cap in place through the period, the
models are persisting with having at least weak instability (250-
1000+ J/kg MUCAPE) above this layer to work on. And while the deeper
shear will lie farther north, could be enough overlap with favored
lift areas to aid convective updrafts. Think a few stronger storms
are possible, and can`t completely rule out an isolated severe. Hail
is the main concern.

> THU-FRI: widespread rain chances

A mish-mash of weather elements are in play over this period with
pieces of upper level energy in the northern and southern streams of
the flow, frontal boundaries, low level jet/moisture transport
interactions, maybe some weak instability to boot. Mix together, put
on blend, and you get more widespread rain chances.

Latest batch of EPS members highlights Thu night for the higher
chances (locally) with all dropping some QPF. The GEFS is about
50/50 with these chances, but still lays down some QPF within the
THU-FRI period. While the details of the higher rain chances, areal
coverage, still aren`t clear - the probabilities say this is the
period where most/all can expect some rainfall.

> SATURDAY: DRY! And the dry conditions could extend through Sunday.

Need to highlight Saturday as it might be the only day that does not
harbor any rain chances for the region. The GEFS and EPS have been
in good agreement with bringing a amplified shortwave ridge in from
the west Fri night, settling over the region Sat. All WPC clusters
concur - and also suggest the ridge would continue to influence the
area into Sunday - potentially giving us a dry weekend. That said, a
few of the EPS and GEFS members are not as hardy with the ridge and
allow for some shortwave troughing to start pushing in from the
west. More rain chances would creep back in, especially westward.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1240 PM CDT Tue Apr 22 2025

As a band of lower VFR & patchy MVFR ceilings progress east
through central Wisconsin early this afternoon, mostly VFR
expected area wide from northeast Iowa, southeast Minnesota, and
western into central Wisconsin through the 22.18Z TAF period.

Subsequent aviation concerns will be storms moving from
southwest to northeast overnight into early Wednesday morning.
Current confidence is moderate to high (50-70%) for storms
primarily affecting smaller airports in the southern half of the
forecast area. Both TAF sites are along the gradient of higher
confidence. Therefore, have left TS/RA mention out of TAF at
22.18Z issuance. May need a PROB30 in coming TAFs. Moderate to
high confidence in MVFR to IFR ceilings accompanying
precipitation and patchy IFR visibilities.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...JAR