-- Discussion containing changed information from previous version are highlighted. --
938
FXUS63 KARX 221743
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1243 PM CDT Sun Sep 22 2024

.KEY MESSAGES...

- Much cooler start to the week (at or below normal), but trending
warmer (5 to 10 degrees above) for the latter half of the new
week.

- Lingering rain chances across northeast IA into central WI this
morning. More low end chances (20%) possible in the same locations
Mon/Tue otherwise looking like a dry week.

&&

.DISCUSSION...
Issued at 225 AM CDT Sun Sep 22 2024

OVERVIEW: Northern stream shortwave continues to track east across
southern Canada today while the cold front that aided the storms of
Sunday sinks further southeast of the local area. Ripples in the
upper level flow still on track to roll across the front today into
Monday, although positioning favored by the short/med range guidance
keeps the bulk of the related pcpn chances south.

Moving into the new work week, the GFS and EC want to take a
shortwave over the southern plains northeast to across IL Tue. Most
of the EPS members suggest the spin will be far enough north to
bring rain chances to the southern third of the forecast area. The
GEFS is just a bit farther south and keeps the region dry.

Meanwhile, another shortwave in the northern portion of the upper
levels is progged to drop southeast over the northern plains Tue.
Models diverge here as the deterministic runs of the EC continue to
shove this feature nearly due east. The GFS, on the otherhand, now
dives it south/southeast, developing a cutoff low over the
southeastern US. The EC does eventually develop something similar
with a different piece of energy, but it`s much weaker and farther
west of the GFS. This is a shift south compared to some previous
runs of the GFS. Both of the competing solutions result in sharper,
more amplified ridge bending over and across the upper midwest/great
lakes - with similar sensible weather outcomes (dry, warmer). Which
solution looks more likely? Looking at the WPC clusters, 2 show
something akin to the GFS while the other 2 look like the EC. There
is a mix of both models` ensemble members in all 4 clusters - not
favoring any one over the other. Looking at previous runs of the
clusters, they have all been trending toward a more amplified ridge
to bend/build in from the west while keeping any trough/cut off low
south/southeast of the region. Confidence increasing that this is
the more likely outcome as a result.


PCPN CHANCES: showers and storms will continue to spark along a
departing cold front - currently running from northeast WI into
southern IA, progged to lie from far southeast WI into MO by 18z.
Rain chances will linger from central WI into northeast IA through
the morning hours, but should clear the bulk of the locally area by
noon.

Rain chances could graze far southern/eastern portions of the
forecast area Mon/Tue, depending on the how far north the shortwave
tracking out of the southern plains moves. NAM/GFS/EC all suggest
the feature could be close enough to warrant at least low end
chances (20%) for some of the local area. A few of EPS members are a
lot more robust with the rain potential but those are in the
minority. Will let the NBM dictate rain chances for now.

The latter half of the week is shaping up dry.


TEMPS: much cooler air spreads across the upper mississippi river
valley today and settles in through the middle part of the new
week. Not appreciable cold with ensembles in good agreement on
topping out highs mostly in the upper 60s to around 70 into Tue
(near or a few degrees below the seasonable norms).

Some warming is then favored by both the EC and GFS ensemble suites
with 75% of their members creeping temps back to/above the late Sep
normals for the latter half of the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
-- Changed Discussion --
Issued at 1241 PM CDT Sun Sep 22 2024

VFR conditions with variable high cloudiness. A storm system is
bringing in high cloudiness aloft, but surface high pressure
and north winds are ushering in much drier air. Dewpoint
spreads remain large for Monday morning despite surface winds
decoupling, thus fog is not expected outside of valley areas in
southwest Wisconsin. Brisk north winds become light and variable
overnight. Easterly 900mb winds remain somewhat elevated 10 to
20kts through 12Z Monday; limiting fog potential.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION...Cecava/Zapotocny