Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 281727
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1227 PM CDT SAT MAY 28 2016

.SHORT TERM...(Today through Memorial Day)
Issued at 314 AM CDT Sat May 28, 2016

A little more straightforward forecast heading through the day (in
theory at least), with the main concern being rains through mid
morning followed by any potential afternoon convective
redevelopment, which could include a few stronger storms. Early
morning analysis places a mid level shortwave working through Iowa,
out ahead of a larger upper trough working through the Central
Plains. Narrow corridor of upper jet support and broad ascent ahead
of the aforementioned lead wave has helped sustain a fairly large
axis of rain slowly lifting north toward the CWA, helped along as
well by more focused moisture transport and a subsequent uptick in
weak instability (elevated CAPE values inching upward toward 250
J/KG). Earlier training echoes into parts of southeast Iowa were
tied to a nicely convergent inverted trough axis and Corfidi vectors
aligned perfectly with the mean flow, though that threat has all but
ended this far north with that trough axis filling over the past
handful of ours, while another surface wave takes over across
central Kansas.

The recent trend for rain and some embedded thunder lifting north
across the CWA should continue for a few more hours this morning,
but just like yesterday, envision a brief break through late
morning/early afternoon with weakish subsidence in the wake of our
lead shortwave. Heading into the afternoon, will have to see how
clouds behave, but envision at least some sunshine working in tandem
with mixed layer dew points into the lower 60s to fuel MLCAPE values
climbing back to around 1000 to maybe 1500 J/KG by 18-21Z. About
that time, should see our next round of broad ascent ahead of the
approaching primary wave, likely resulting in at least scattered
shower and storm redevelopment. That activity may have some chance
to get a little more organized from far northeast Iowa into
southwest Wisconsin within an axis of increasing deep layer shear,
though progged veer/back/veer wind profiles aren`t necessarily the
best for organized supercellular development. Still, with the
potential for some localized backed 0-0.5km flow ahead of an
approaching surface wave and relatively lower freezing levels with
cooling aloft, will have to watch for perhaps a sneaky brief tornado
spin-up and/or some hail potential with any stronger cells.

Passage of the wave and eventually a cold front later tonight into
should gradually shut down the risk for remaining showers toward
sunrise Sunday. Heading into Sunday afternoon, really have a hard
time buying into NAM/GFS depiction of afternoon shower redevelopment
with big issues in their dew point schemes. Per a glance at our
incoming post-frontal airmass up across the northern Plains, feel
dew points are likely to mix into the 50s, really limiting any
diurnal instability...not to mention the potential for pesky stratus
to hang tight for a while behind the front on Sunday. With that
said, some risk for remaining showers does appear warranted,
especially north of I-90 with latest trends suggesting the upper
trough axis will be a touch slower to exit. Sunday night looks dry
with shortwave ridging building overhead, with confidence not
exactly the highest regarding precip chances for Memorial Day
itself. Recent runs of the NAM/GFS have latched onto the idea of
that shortwave ridging hanging tight through Monday, while the
GEM/ECMWF continue to show better moisture return ahead of a digging
upper trough working back into our southern CWA, supporting chances
for more showers and storms. Given the uncertainty, prefer to just
run with continued small-ish POPs across southern areas and see
where future trends take us.

.LONG TERM...(Monday Night through Friday)
Issued at 314 AM CDT Sat May 28, 2016

Not a whole lot of change in the expected setup heading toward
midweek, with a stronger northern stream wave progged to work across
the northern Plains before lifting into Ontario and helping
potentially carve out a deeper trough across the Upper Midwest and
Great Lakes. Still quite a few questions about how much upper
forcing will work down this way, but the overall idea for more
shower and storm chances remains intact, especially Tuesday into
Wednesday. Thereafter, a much clearer signal is emerging that the
late week period will feature some much cooler conditions as upper
troughing takes hold while low level ridging dominates with dry and
quite comfortable conditions to begin the month of June.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1227 PM CDT Sat May 28 2016

Primary concern is watching thunderstorm potential this afternoon
and evening. Forecast guidance in good overall agreement showing
thunderstorms currently developing across south-central IA lifting
north and east through this evening, potentially impacting KRST
and KLSE between 28.21Z and 29.02Z. While VFR conditions will be
the general rule, MVFR (maybe IFR) conditions are possible with
stronger thunderstorms that move over TAF airfields. Once storms
move north and dissipate later this evening, will need to watch
the potential for more widespread MVFR/IFR ceilings overnight. For
now, will lower ceilings into the MVFR range, but may need to
lower further as details emerge. Light southerly winds will shift
to the west-northwest and increase overnight into Saturday
morning.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...ROGERS


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