Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211712
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1212 PM CDT Mon May 21 2018

.SHORT TERM...(Today through Tuesday)
Issued at 215 AM CDT Mon May 21 2018

Two distinct curls in latest watervapor satellite imagery, with
shortwaves driving northeast across ne and mo. Both were triggering
showers along their leading edge.

The MO wave is progged to lift into southern WI by the afternoon
while the other shortwave shifts into southern MN, then takes a
right turn east overnight. Some frontogenetic banding lifts
north/northeast across the area ahead of the shortwaves. Showers
with the farther west feature are likely to lift more due north this
morning, per radar trends and shortwave movement. The other
shortwave has more a northeast tack, plus also has some feed of weak
low level moisture. This area should continue to expand as it moves
into northeast IA/southern WI this morning, lifting across northern
WI this afternoon. pcpn chances look fairly spotty after that - even
with the second shortwave moving through.

Weak high pressure builds in for Tue, promising a day off from the
on-off rain. Clouds might be a little slow to clear from west to
east.

Another very cool day for most of the area with abundant clouds and
that rain. Starts to warm back up for Tue - how much dependent on
how quickly those clouds can clear.

.LONG TERM...(Wednesday through Sunday)
Issued at 215 AM CDT Mon May 21 2018

Models have been in pretty good agreement over the last couple days
with taking a weak shortwave/mcv from the central/southern plains
into/across a weak 500 mb ridge - inching it toward the local area
late Tue night-Wed. A little frontogenetic lift on the leading edge
of the shortwave, but as it moves east, it moves away from the main
trunk of low level transport and the CAPE pool. West-east x-sections
also show a lack of saturation as you move east of the Mississippi
River - where the shortwave is trying to climb across the weak upper
level ridge. Enough going for it that scattered/areas of showers
should push into IA and southern MN overnight Tue - but how far east
they eventually make it is in question. With the overall flow still
relatively weak, not a big push to get this feature across the
region. Could stall out, weaken, or be shuffled more north -
skirting eastern parts of the local forecast area. Will sketch out
rain chances with that mind - higher to the west, smaller in the
east.

Shortwave trough still slated to lift northeast out of the Rockies
Thu, slipping across the northern plains and then across the upper
mississippi river valley Friday night. This has been a consistent
signal in the models - although timing, strength has varied - with
the weak flow having a lot to do with that. Low level warming will
lead the shortwave across the region and there does look to be some
850 mb moisture transport to feed shower/storm chances. GFS
continues to be well-cooked when it comes to SBCAPE, over doing its
sfc Tds by about 10 degrees. Still, looking at around 2K J/kg of
MUCAPE to aid convection potential. Shear still awfully weak.
Expectation is for showers/storm chances to persist on Thu,
advancing more east as saturation improves and a leading piece of
energy spins ahead of the main trough. Rain chances continue Fri,
and then into sat as the trough moves through. Overall, fairly wet
few days with on-off showers with a few thunderstorms. Severe risk
looks low at this time.

Going to be warmer for the later half of the week, even with the
clouds and rain threat. Weak ridging and a return to more southerly
flow will see to that. Highs should reach/top 80 at many locations.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1212 PM CDT Mon May 21 2018

Local and regional radars suggest the showers will be past or very
close to being past KRST by 18Z and plan to start with a dry
forecast. The showers should end by the middle of the afternoon at
KLSE and will carry them through about 20Z. Ceiling heights are
not expected to move much today with a very weak pattern in place
over the region. With the rain priming the low levels of the
atmosphere and light winds overnight, concerned about fog forming
and producing MVFR/IFR conditions at both airports. Any fog the
forms overnight should dissipate by mid morning Tuesday allowing
the visibility to come back up, but ceilings will be much slower
to improve with these coming up from IFR to MVFR. These could also
improve to VFR by late Tuesday morning, but confidence is not high
enough to include at this time.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...04



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