218
FXUS63 KARX 011853
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
153 PM CDT Wed May 1 2024

.KEY MESSAGES...

 - More showers and storms expected Late tonight through
   Thursday. Pockets of heavy rain are the main threat with a
   lower risk for a severe thunderstorm or two.

 - Active weather pattern continues into next week with a dry
   day in between different weather systems.

&&

.DISCUSSION...
Issued at 148 PM CDT Wed May 1 2024

Showers and Scattered Storms Tonight and Tomorrow:

Even as previous wave is exiting northern Great Lakes, already
looking at next mid level system ejecting out of mean trough out
west. As this next wave approaches, look for broad lift and fairly
rapid low-level moisture return into the Plains and Upper MS Valley
tonight into Thursday. This is depicted well on moisture transport
outcomes. Channel of higher precipitable water values will also
advect north ahead of this wave setting up more rounds of showers
and embedded storms next 36 hours.

Another fairly messy system for our area with main wave moving
northeast as it swings through trough. This may keep better shear to
the northwest and disconnected from better instability to the south.
In addition, convection will be moving in early Thursday that could
muddle any severe weather risk, at least initially. Most likely
scenario is we see rounds of showers and a few non-severe storms
with maybe some hail, gusty winds, and periodic heavy downpours. A
smaller chance /5-10%/ exists that a break in the convection could
allow for some late day redevelopment along the front leading to a
bit stronger storms, but still, odds are in favor of that staying
south of the immediate area.

Another item we will need to watch is total rain. The precipitable
water values are not as high compared to earlier model solutions but
still looking at fairly deep layer for efficient rain producers.
Mean total rainfall keeps 1 to 2 inches mainly across northeast Iowa
and points south with lighter amounts north of there. Even looking
at probability of getting an inch or more centers on southern areas,
not as widespread as earlier thought. This makes sense given areas
to the south could remain more in the warmer sector with higher
instability going into late Thursday. River basins have been
handling each round of rain well, but may start to see higher
responses as each one of these systems pass. Flash flood guidance
has also been dropping as we gradually saturate.

Weekend Weather Outlook:

A persistent longwave trough pattern across the western CONUS
continues to eject shortwave troughs out of the Intermountain West
this weekend into next week resulting in periodic shower and storm
chances through the extended forecast. After showers and storms move
out of the forecast area early Friday morning, a drier day takes
hold with weakly-forced high pressure moving in overhead. The next
shortwave trough makes its passage across the Upper Mississippi
Valley on Saturday. Differences in timing, coverage, and
precipitation amounts remain, but confidence is high that this will
be a weather system void of severe weather potential locally.
Showers are the favored precipitation type with weaker forcing and
very little CAPE present in long-range ensemble forecasts but a few
storms across the southern half of the forecast area cannot be
ruled out.

Looking Ahead to Next Week:

Confidence is increasing for a stronger low pressure system early
next week. A cursory look at the global models and ensembles show a
mid-level closed low developing somewhere in the Northern Plains
region with pockets of strong potential vorticity advection (PVA) in
its cyclonic flow. The strongest period of PVA is currently progged
to arrive Monday night when an embedded shortwave trough could
propagate northward along the Upper Mississippi Valley. While the
details about the evolution of the closed low remain unclear at this
time, all signs are pointing to more active weather for the week
ahead.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1238 PM CDT Wed May 1 2024

Besides some MVFR ceilings to the north, that are becoming more
cellular, VFR conditions prevail with a fairly brisk west to
northwest low level flow. The winds will diminish quickly going into
the evening as we are start to feel impacts from approaching trough
that promises to bring abundant convection back to the area starting
late tonight.

As ceilings gradually lower overnight, expect VFR conditions to last
for a bulk of the time but as lift and moisture advection continues,
we will see gradual drop to MVFR to IFR ceilings, especially as bulk
of convection impacts area early Thursday. Details on the impacts
from thunderstorms will have to be resolved in near-time.

&&

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

&&

$$

DISCUSSION...KAA/Shea
AVIATION...Shea