Area Forecast Discussion
Issued by NWS La Crosse, WI

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566
FXUS63 KARX 220731
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 AM CDT Sun Oct 22 2017

.SHORT TERM...(Today through Wednesday)
Issued at 230 AM CDT Sun Oct 22 2017

Cold front and associated line of convection making steady progress
east early this morning, and will shift across eastern WI as the
morning wears on. The parent 500 mb trough still off to the west
though - moving into western MN per latest water vapor satellite
imagery. Meanwhile, closer to the surface a west-east running
time/height x-section shows a sloping frontogenetic region holding
across the area into the afternoon. Drier air gradually undercuts
the saturation available for the frontogenetic/upper level forcing
to work on - evidenced in the x-section and soundings. Expect some
showers to linger/spark post the front - especially for western WI.
How quickly the drier air moves in will be key on where the showers
persist through the afternoon. As it sits, most of the chances
should east of the mississippi river.

The models have been in good agreement with dropping a shortwave
southeast out of Canada for the start of the new work week, sweeping
the trough axis southeast Mon night, but keeping the region under
northwest flow with bits of energy rippling along the backside of
the trough Tue. The system will bring its own saturation with it,
and will have enough to generate scattered/areas of showers
regionwide Monday, then mostly across the eastern half of WI Tue. A
shot of colder, Canadian air is brought southward with the trough
and temps will tumble accordingly. Highs not likely to reach 50 for
much of the local area Tue.

With the cold air in place, a secondary piece of upper level energy
drives down the backside of the departing trough for Tue night/Wed.
This feature should bring some more pcpn chances - but this time in
the form or rain and/or snow. Progged trajectory in the various
models favor keeping chances mainly across WI.

.LONG TERM...(Thursday through Saturday)
Issued at 230 AM CDT Sun Oct 22 2017

The next shortwave drops across the ridge over the west coast,
driving southeast over the plains and carving out yet another upper
level trough for the nation`s mid-section. Differences between the
GFS and EC with whether the upper level low will eventually close
off, positioning of the sfc features, etc. They both agree that
another reinforcing shot of cold air will come with the digging
trough - dropping 850 mb temps to -8 C or so for next weekend. Highs
would be hard pressed to warm out of the 40s in this scenario. Most
of the accompanying pcpn is progged to fall north and west of the
sfc low, and would have the opportunity to be rain and snow. Some
convection should fire along a cold front to the south, but trends
point to keeping this threat south of the local area for now.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1140 PM CDT Sat Oct 21 2017

A cold front continues to gradually work through the region, and
should clear LSE by 06Z. Earlier band of thunderstorms along that
front has pushed east, but a larger axis of rain will continue to
impact LSE for a few more hours, while RST should now be clear of
the rain (can`t rule out a brief shower through 07Z). Current MVFR
ceilings at LSE will improve to VFR by 07Z, further rising through
the coming day for most areas as drier air works into the region.

With that said, rain does look to hang on much longer east of LSE
through at least midday, and it is possible that some showers will
linger at that site longer than currently indicated. Should that
occur, however, ceilings will still remain VFR for LSE proper.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence



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