447
FXUS63 KARX 111149
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
649 AM CDT Sat May 11 2024

.KEY MESSAGES...

- Warm Sunday with afternoon-evening shower/storm chances (30-50%).
Highs could push into the mid 80s for some river valley locations.

- Cooler Monday with rain chances lingering (mostly south of I-90).

- Periodic rain chances for the new work week with temps expected to
hug close to the seasonable normals (around 70).

&&

.DISCUSSION...
Issued at 225 AM CDT Sat May 11 2024

* SUNDAY/MONDAY: Warm Sunday, afternoon-eve shower and storm chances
  (30-50%). Shower chances linger south Monday, cooler/seasonable.

Upper level shortwave ridging set to drop southeast across the
region Sunday. 850 mb temps progged to warm from around +4 C at 12z
Sat to +13 C by 18z Sun. South, southwesterly fetch will help with
the warming, all ahead of a cold front dropping southeast across the
upper mississippi river valley for the afternoon/evening. Mixing is
fairly deep for the afternoon, promoting drying and increasing wind
gustiness, but will also help in the warming. 11.00z HREF paints a
40-70% chance for highs to push north of 80 degrees for all
locations along/south of I-94. River valley locations (sandier
soils) likely to have the largest bump in temps and could see some
mid 80s. A taste of summer, minus the humidity.

Back to the cold front...this sfc boundary is associated with an
upper level shortwave trough which is set to slide across far
northern parts of the region Sun/Sun night. Fgen along the front is
meager, mostly low level, while the bulk of the low level
thermodynamics is off to the east. There will be instability to play
with as both the GFS and NAM paint 1000-1500 J/kg of SBCAPE by mid
afternoon. Checking out the forecast soundings, deep mixing will
promote some drying - so these CAPE values could be too high
(dewpoints could be over forecast by the models). No shear to speak
of. So a weakly convergent frontal boundary, not much for upper
level support, but some instability to work with, suggests at least
chance pops for showers/storms (30-50%).

The front lays up west-east across northern IA/southern WI on
Monday. A shortwave trough in the southern portion of the flow will
meander across the southern plains and mid mississippi river valley,
working on the boundary and helping to spark another round of
showers/storms along it. Rain chances look more widespread with a
more moist airmass to work on (pws climb to 1 1/4"). MUCAPES upwards
of 500 J/kg with (again) not much for shear. Medium range guidance
holds most of the rain chances south of I-90 with the pcpn threat
shifting east by mid evening.


* NEW WORK WEEK: progressive upper level flow, periodic rain
  chances, seasonable temps

A variety of perturbations in the upper levels of the atmosphere are
set to shift west-east across the CONUS for the new work week. GEFS
and EPS showing some differences in placement/timing of the
potential rain makers. Model blend thusly "smears" the pcpn chances
due to the disagreements - spreading the threat out over several
days while also holding lower end chances. Confidence also takes a
hit in highlighting any period for having higher chances (or dry for
that matter) - at least at this time. Will continue to ride the
blend, but expect some refinement to the forecast as we move into
the early part of next week.

As for temps, after what looks to be a warm day Sunday temps are
progged to settle back to more seasonable levels (or a few degrees
above). That said, still a lot of spread in the ensemble members and
certainly some adjustments for pcpn/no pcpn to be had - which isn`t
clear. Again, will let the blend make the call for now.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 650 AM CDT Sat May 11 2024

VFR expected through the 11.12Z TAF period. Northwest winds
slightly increase today primarily west of the Mississippi
River. These winds wane tonight, eventually turning out of the
south near 12.00Z or shortly thereafter.


&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...JAR