Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 222337

Area Forecast Discussion
National Weather Service La Crosse WI
637 PM CDT Sun Oct 22 2017

.SHORT TERM...(This evening through Monday)
Issued at 220 PM CDT Sun Oct 22 2017

Early this afternoon, surface analysis depicted a cold front over
far eastern Wisconsin southwestward into the Mid-Mississippi Valley.
Post-frontal rain showers associated with a sloping zone of
frontogenesis have been slow to progress eastward, but expect the
rain to clear western/central Wisconsin by late afternoon, with
strong subsidence behind an elongated ribbon of vorticity helping
to clear skies out from the west. By early this evening,
generally clear skies are expected as high pressure briefly noses
into the area.

Later tonight, mid/high clouds will begin to increase from the
northwest ahead of an upper trough and associated cold front
approaching from the northwest. As forcing from the upper shortwave
increases along with mid-level frontogenesis, some showers could
swing east Monday morning. NAM soundings are quite dry, so how much
rain actually reaches the ground is in question. As a result, kept
only low rain chances. Additional isolated to scattered diurnally
driven showers may swing southeastward beneath the cold upper trough
by later in the afternoon. Despite increasing low-level cold
advection behind the front, temps still will reach near seasonal
norms, although northwesterly winds will become gusty especially
west of the Mississippi during the afternoon as boundary layer
mixing increases and 925 mb winds increase to near 30 kts by late in
the day.

.LONG TERM...(Monday night through Sunday)
Issued at 220 PM CDT Sun Oct 22 2017

The upper level flow will continue to transition to northwest
flow as the mean long wave ridge builds over the western conus.
The short wave trough that will drop across the Upper Midwest
Monday will help form a cut off low over the Great Lakes Monday
night. This low will then move to the north and quickly become an
open wave as another short wave trough comes out of central Canada
and into the Great Lakes Tuesday night. This wave will quickly
move by the area allowing some short wave ridging to build over
the area for late Wednesday and Wednesday night. The next short
wave trough in the northwest flow will then drop out of central
Canada and is expected to have another closed low form over the
Upper Midwest Thursday with the trough from this system remaining
over the Great Lakes region into the upcoming weekend. This
pattern will bring several periods for light precipitation chances
along with cooler temperatures.

The first chance for precipitation will continue from Monday into
Wednesday and should mainly be over Wisconsin in the wrap
around/deformation of the surface low moving north through the
eastern Great Lakes. Temperatures with this system should stay
warm enough for the precipitation to fall as mainly just rain but
it may get cold enough Tuesday night for a chance of some light
snow. With the ridging aloft, it then looks like there should be a
dry period Wednesday afternoon and night before that next system
drops into the region from Canada. The surface low with this
system looks to move southeast into the Upper Midwest Thursday and
remain over the region Thursday night. Some differences now
between the 22.12Z ECMWF and GFS on how long this system will
remain. the ECMWF has transitioned to kicking both the upper level
and surface system out of the area by Friday night while the GFS
holds the whole system back which would linger some light
precipitation over the area through much of the upcoming weekend.
This system does look like it will bring another shot of cooler
air to the region with highs in the 40s expected for Friday
through Sunday. Temperatures at night will be cool enough for the
precipitation to possibly fall all as light snow with lows
dropping into the 20s for Friday and Saturday nights.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 637 PM CDT Sun Oct 22 2017

High pressure has briefly built into the region, but will depart
late tonight as a cold front marches in from the west. A lingering
area of thick cirrus will very slowly drift through Wisconsin
overnight (clearing line right over LSE at 00Z), but with mainly
clear skies and southerly winds of 6-12 knots for LSE/RST through
about sunrise. Thicker mid level clouds are then expected to
quickly arrive from the west, right ahead of the cold front, with
a few showers possible just about anywhere as the front passes.
Behind that feature, winds shift northwest and become gusty for
the afternoon, with surface gusts of 25 knots or higher possible
at RST (slightly lower at LSE).




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