779
FXUS63 KARX 310341
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1041 PM CDT Thu May 30 2024

.KEY MESSAGES...

- More showers, a few storms for Friday into Friday night
  (40-70% chances). Lower end amounts expected (few hundreths
  to upwards of 1/4").

- More storm chances Sunday night/Monday. Some potential for
  strong to severe, depending on timing.

- Warming as we move into the new month with highs expected to
  meet/exceed the early June normals.

&&

.DISCUSSION...
Issued at 220 PM CDT Thu May 30 2024

OVERVIEW: fairly progressive, quick moving upper level flow into the
middle part of next week promising to push shortwave ridges/troughs
across the upper mississippi river valley. Periodic rain chances
will continue, with no prolonged period to "dry out" in the near
term. Some potential for severe storms too - highly dependent on
timing/positioning of the upper level features/sfc fronts. Overall
height increases a loft support some warming as we move into the
weekend/next week - not "hot" per se, but the recent run of highs in
the 60s/70s should push to, and a few degrees above, the seasonable
normals as we creep into the start of June (mid 70s to around 80).

Venturing into the following weekend, long term guidance suggests
ridge building will occur over the west coast/plain states. Some
differences between the GEFS and EPS here, but the upshot would be
to carve out an upper level trough over the great lakes...which
could mean more showery and cooler conditions. Something to watch.


FRIDAY/FRI NIGHT: rain, storm chances

Elongated bit of upper level shortwave energy stretched north-south
across the dakotas at early afternoon, per latest upper water vapor
satellite imagery. The shortwave, along with an associated cold
front at the sfc, were serving to fire shower/storms - fueled by a
ribbon of instability/moisture transport. Not too perky as of yet
but should see some increase in intensity/areal coverage as the
afternoon wears on.

The system gradually moves east tonight, but not in a hurry, and
short term guidance points to weakening in the overall forcing. CAMS
models bring the pcpn to the forecast area`s doorstep (SE MN) by
12z, but questionable on how much further east the chances make
through the day. Most of the short term guidance hold the sfc
boundary/convergence from northwest WI into northwest IA while the
upper level shortwave shears out north and south. Eventually, the
sfc front, instability axis and fetch of moisture transport bend
across the local area, spreading rain chances eastward but currently
on the "lower end" (sub 50%). All in all, the higher chances and
greater rainfall amounts continue to be favored from northwest WI
into northwest IA.


SUN NIGHT/MON: storm chances, strong to severe possibilities

Medium/long range guidance remains in solid agreement with tracking
an upper level shortwave trough across the northern plains Sunday
with some reflection at the sfc. Disparities in how strong the
shortwave will/could be, along with the frontogenetic lift with the
sfc front. Warm, moist unstable airmass pools over the northern
plains to fuel storm chances with PWs upwards of 1 1/4" and SBCAPES
of 2500 J/kg. Wind shear enough to aid storm organization.

Current GEFS/EPS runs favor tracking the storm system across the
local area Monday morning/early afternoon. CAPE pool shifts
southeast Monday in this scenario, moreso across IA and northern IL.

With the current timing, showers and storms would fire over the
northern plains Sunday afternoon, shifting into western MN for the
evening. Some severe weather looks like a good bet. As the storms
shift east overnight, decreasing instability and increasing sfc
based CIN would work to downscale the severe threat. Then on Monday,
morning pcpn/clouds will conspire against quick destabilization,
which would shift most of a strong/severe threat south/east of the
local area. Very timing dependent - so keeping a close eye on
evolution, location of the main features.


TUE NIGHT/WED: another round of storms?

Long range guidance pointing to another, but stouter shortwave
trough would drop across the northern plains and then the upper
mississippi river valley Tue night into Wed. In this case,
instability not looking as robust as Sun night and shifted
southward. Low level jet/moisture transport looks to drive northward
ahead of the system and PWs could push north of 1 1/2". Another good
shot for storms, but uncertainties for any strong/severe storm
potential.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1040 PM CDT Thu May 30 2024

Main taf concerns are showers and potential for thunder at both
LSE/RST taf sites. A weak surface front slowly moves east across the
area Friday. Weak convergence and very limited instability will
allow a few showers to develop early Friday afternoon along the
front. Due to very little instability...thunderstorm chances are low
and will keep mention out of tafs. Latest trends show slower
movement of front moving across the region. Have delayed the onset
of the possibility of showers into the taf sites...especially the
RST taf site. VFR conditions are expected to prevail through the
much of the taf period. However...if a stronger shower moves over
the taf sites...a brief period of MVFR conditions could occur Friday
afternoon/evening. Southerly wind speeds will be around 10 knots or
less.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...DTJ