537
FXUS63 KARX 010335
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1035 PM CDT Fri May 31 2024

.KEY MESSAGES...

- Showers, a few storms continue tonight into Saturday. Severe
weather not expected but locally heavy rains possible into early
evening.

- More rain chances Sunday night/Mon and again later Tue into Tue
night. Some threat for strong/severe storms, moreso Tue
evening...but ample uncertainties in timing/placment of
responsible weather makers. Heavy rain potential. Something to watch.

- End of next week trending cooler with occasional showers.

&&

.DISCUSSION...
Issued at 225 PM CDT Fri May 31 2024

TONIGHT/SAT: areas of showers, a few storms

A bit of upper level energy with a cold front reflected at the sfc
working on a 1000 J/kg pool of SBCAPE to fire areas of showers and
storms across parts of IA, MN and northwest WI this afternoon. Some
of the CAMS suggest an uptick in intensity by late afternoon/early
evening. Instability is marginal with weak shear - so not expecting
anything too perky (no severe locally but a strong storm or two not
out of the question).

The showers will continue into the overnight with a few cracks of
thunder but overall coverage should be on the decline with decrease
in instability (loss of daytime heating).

The pcpn looks to shift east/southeast of the local area toward the
noon hour, but recent CAMS runs suggest a thin line of convection
could fire in the afternoon, in a ribbon of instability with some
lingering convergence along the system`s cold front and/or
differential heating between sunny/cloudy region post the morning
rains. Here again, very skinny CAPE profile in the vertical and not
much shear to work with (limiting/eliminating a strong/severe risk).
Enough potential to continue smaller end rain chances (20-40%)
through the afternoon.


SUN NIGHT/MON: more rain chances

Another shortwave trough and attendant cold front will be pushing
across the northern plains Sunday. Line of showers/storms should
spark along the leading edge of the system, and with ample buoyant,
moist air to play with, strong-severe storms appear to be a solid
bet. These are progged to slide over western MN Sun evening and
continue to the Mississippi River overnight. They should be
diminishing in intensity and coverage with loss of daytime heating
(instability), increasing near sfc CIN, and some weakening in the
low level jet/moisture transport.

Showers and a few storms likely persisting over the region Monday as
the shortwave/front continues to exit east. Clouds, pcpn will favor
holding the greater pool of instability southward, limiting
potential for strong storms locally.

Of course, all this depends on timing. While the EC and GFS
generally favor the aforementioned solution (as do their ensemble
members), the NAM does not. The 31.12z NAM is about 12 hours slower,
which would end up bringing the front in later in the day - where
more instability could/would be available, and raises the specter of
stronger storms.

For now, will stick with the GFS/EC solution - but keep an eye on
evolution as we move into the new work week.


TUE/TUE NIGHT: another round of storms, some could be strong

Long range guidance has been in good agreement with dropping a more
robust upper level shortwave across the northern plains Tue,
spinning across the upper mississippi river valley Tue
afternoon/evening. Relatively warm, moist air pools ahead of the
attendant cold front with PWs currently looking to push upwards of 1
3/4" while MUCAPES could climb 2000+ J/kg. Some wind shear to play
with, aiding convective potential/development. Obviously too far out
to put any definitive statement on what to expect, but depending on
how quickly the system moves, there would be the potential for
strong/severe storms across parts of the region. In addition, warm
cloud depths progged by the EC and GFS to tickle 4K m...pointing to
efficient rain makers...suggesting a heavy rain threat. North-south
orientation of any rain band and progressive nature west-east would
work against prolonged heavy rain, but a localized concern
certainly. Something else to keep an eye on as we move into the new
work week.


LATTER HALF OF NEW WEEK: blocking pattern? Trending cooler,
occasional showers

GEFS and EPS runs over the past couple days continue to carve out an
upper level trough over the eastern great lakes/new england states
while amplifying a ridge along the west coast. They start to disagree
with whether this pattern will hold through the weekend, or show
some progression east. WPC cluster analysis bears this out
suggesting both solutions are possible...with the bulk of the EPS
favoring holding the pattern in place while most of the GEFS nudge
the ridge eastward. The EPS would bring cool air in, and hold it
there, through the weekend along with periodic shower chances. The
GEFS also returns cooler air, but suggests some moderation toward
week`s end. It would still favor those shower chances.

Upshot for sensible weather? Still looking like a return to cooler
than normal temps either way, with occasional shower chances. How
long the colder air sticks around, and how widespread rain chances
would be, remain question marks.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1035 PM CDT Fri May 31 2024

Main taf concerns are MVFR/IFR conditions at both RST/LSE taf sites
after 12z Saturday. Surface front will slowly move across the area
tonight. Behind the surface front...ceilings are expected to lower
into MVFR at both RST/LSE taf sites after 12z Saturday. However with
less rainfall across the region...there are hints the MVFR
conditions could be brief during the day. For now...have kept a
period of 6 to 8 hours of MVFR conditions during the day Saturday
with improving conditions middle of Saturday afternoon. There is the
possibility of showers moving over the taf sites overnight/Saturday
morning along the front. Have mention of vicinity showers and brief
period of showers early Saturday morning. Latest hi-resolution
models also suggest isolated showers/storms developing in the
afternoon across the area. Based on coverage will not mention in the
RST/LSE tafs.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...DTJ