014
FXUS63 KARX 151943
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
243 PM CDT Wed May 15 2024

.KEY MESSAGES...

- Showers move through overnight with additional thunderstorms
  possibly developing east of the Mississippi River Thursday
  afternoon. Can`t rule out hail with storms tomorrow
  afternoon.

- Seasonably warm temperatures in the 70s to low 80s through the
  weekend.

- Next rounds of showers and storms come Saturday, more active
  period for showers and storms shaping up for the first part of
  next week (predictability low at the present time).

&&

.DISCUSSION...
Issued at 240 PM CDT Wed May 15 2024

Tonight and Thursday: Multiple Rounds of Showers and Storms

A predominantly zonal flow exists this afternoon across the
CONUS with a few waves of note across the country. One such wave
axis was evident across the western Dakotas in water vapor
imagery with a weak surface low reflection over the northern
Siouxland region driving a broad swath of showers and isolated
thunderstorms. This complex slides eastward tonight, with the
short-range guidance struggling to resolve how the precipitation
shield will evolve during this time owing to a lack of both
instability and favorable wind profiles. Overall impacts tonight
will be minimal outside of some heavier showers and occasional
lightning.

The convective complex works ahead of the surface front by the
morning hours, and depending on how much recovery takes place
in its wake, we may see redevelopment along the surface trough
in the early afternoon on Thursday east of the Mississippi
River. A 70-kt upper level jet overspreads the region as it
rounds the base of the upper trough, lengthening hodographs
ahead of the frontal boundary. The biggest question revolves
around how much recovery can take place ahead of the front
before it clears the region. The 12/18Z HRRR runs show about
1000-1400 J/kg of SBCAPE developing ahead of the trough, but it
remains to see if this scenario will pan out. If storms do
manage to form, hail of 1-2" in diameter would be the main
threat. Explicit composite reflectivity progs from members of
the 12Z HREF do lend credence to a line of convection developing
by 18-20Z and exiting the area by 22-23Z, but a small change in
the thermodynamic environment could quickly change this
scenario. Linear hodographs would support storm splitters and
mergers, so the line would grow upscale quickly as it advances
eastward into south-central WI during the mid to late afternoon
and morph into more of a wind threat.

Saturday and Early Next Week: Next Rounds of Rainfall

Split flow brings dry conditions for Friday, with the
progressive flow ushering the next negatively-tilted shortwave
through during the afternoon and evening on Saturday. With the
shortwave already recoiling to the north and taking the 100-kt
300-mb jet with it, there is some uncertainty as to how much
development takes place along the attendant surface front that
slides into our area. Forecast soundings from the GEFS members
don`t show much for inhibition ahead of this front (albeit with
lower CAPE values), so it is probable that we`ll see some
scattered storms with this surface forcing. Overall impacts
will be limited in space and time owing to the lack of deep
shear and compact hodographs.

Attention then turns to early next week as longwave troughing
deepens over the western CONUS, ejecting multiple weak
perturbations through the region between Sunday and Tuesday.
The subtle nature of these waves makes them tough to pin down
more than a few days out. Looking though the 12Z guidance, odds
are better that the surface baroclinic zone will stay south of
the region and take the severe weather threat with it. That
being said, there is plenty of variability in the ensemble
members and such factors will be increasingly driven by how the
previous day`s convection unfolds. This longwave ejects Tuesday
and may be enough to lift the warm sector into the region, but
confidence in such a scenario is low at the present time.

Temperature Trends into Next Week

Overall, expect at or slightly above average temperatures for
the remainder of the week and into next week with highs in the
70s to low 80s and lows in the 40s and 50s. Despite the passage
of a weak cold front Thursday night, warm 925-700-mb southwesterly
flow builds in its wake across the High Plains for Friday and
Saturday. Some of this warmer lower tropospheric air spills
eastward into the Driftless region and allows highs to creep
into the low 80s during this period. Confidence in the
temperature forecast wanes slowly as we head through the first
half of next week owing to the aforementioned precipitation
uncertainties, but the pattern definitely favors at or above
average temperatures with no cold snaps on the horizon.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1225 PM CDT Wed May 15 2024

VFR conditions are expected for the rest of the daytime hours,
with ceilings gradually lowering overnight as rain showers move
through from west to east. The heavier showers will be capable
of MVFR/IFR visibility restrictions. A few thunderstorms are
also possible, but confidence was not high enough to mention in
the TAFs. These showers shift east of the Mississippi River for
the morning hours. Ceilings fall to MVFR levels in the wake of
these showers and persist for the remainder of the TAF period.
Winds of 5-10 kts from the east/southeast this afternoon veer to
the south overnight and continue shifting to the southwest
Thursday morning.

&&

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

&&

$$

DISCUSSION...Skow
AVIATION...Skow