Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 201057
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
555 AM CDT Wed Sep 20 2017

.SHORT TERM...(Today and tonight)
Issued at 357 AM CDT Wed Sep 20 2017

At 3 AM, a cold front was approaching the area from western
Minnesota and western Iowa. A squall line raced ahead of this
front overnight, but as the best forcing moved northeast into
northern Minnesota and mixed layer CIN has increased this line
has been weakening. This trend should continue early this morning.
At this time, the best chance of showers and storms will be north
of the Interstate 94 corridor this morning.

Additional showers have developed near the Interstate 90 corridor
within the past hour. These showers are associated with a wing of
moderate 850 mb moisture transport. The 20.00z models are in
agreement that this moisture transport will move northeast of the
area by sunrise. Due to this, expect that these showers will
become isolated south of Interstate 90 this morning.

For this afternoon and evening, a cold front will move east
through the area. Mixed-layer CAPES will climb into the 1500 to
3000 J/kg range. Like the past couple of days, the best shear will
be found north of Interstate 94. This area will see enough deep
shear sufficient for supercell development. Meanwhile, the
remainder of the area will see the strongest shear in the 0-3 km
layer. Overall, it continues to look like there will be marginal
threat of severe weather between 4 PM and 8 PM over western
Wisconsin. The main severe weather threat will be hail and gusty
winds.

.LONG TERM...(Thursday through Tuesday)
Issued at 357 AM CDT Wed Sep 20 2017

On Thursday, the cold front that moves through the region late
this afternoon and tonight will move north through the region.
With there not being much convergence along this front and capping
aloft, kept the forecast dry.

On Friday, a very warm air mass will be located across the Upper
Mississippi River Valley. 925 mb temperatures on Friday will be
around 27C. As these temperatures mix down with diurnal heating,
temperatures will warm to around 90F. There may be even some mid-
90s in the river valleys. These temperatures will be warm enough
that some locations could potentially tie or break their record
high temperatures for this date. Many of these records were set
back in 1937.

On Friday night, the combination of southerly winds and dew points
in the mid-60s will keep the temperatures very warm. Low
temperatures on Saturday morning will range from the mid-60s to
lower 70s. These temperatures will be warm enough that some
locations could potentially tie or break their record warmest low
minimum temperatures for September 23.

On Saturday, both the GFS and GEM are indicating that some showers
and storms may develop over southeast Minnesota and north-central
Wisconsin during the afternoon. However, the soundings suggest
that the area will remain capped, so continue to question that any
rain will occur. This would be in agreement with the NAM and ECMWF
which keep the rain well to our northwest and north. In addition,
the soundings show very little clouds. As a result, it looks like
we will mix even deeper than Friday afternoon. High temperatures
will be once again be around 90 degrees. These temperatures will be
warm enough that some locations could potentially tie or break
their record high temperatures for this date.

From Sunday into Monday, the 20.00z models continue to differ on
when the upper level ridge will break down. The GFS breaks down
this ridge sooner. As a result, it brings rain into the area on
Sunday. Meanwhile, the ECMWF keeps the area dry through Monday
afternoon. Overall, the ECMWF solution makes the most sense, so
moved the eastern extent of this rain further west and northwest.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 555 AM CDT Wed Sep 20 2017

Cigs: band of mvfr cigs developing out ahead of an approaching sfc
front early this morning. Meso models/bufkit soundings suggest they
could impact the TAF sites for the better part of the morning before
breaking up/clearing as the front slides through.

Expect VFR for the afternoon-night, although some hints of
increasing/pooling low level moisture in the south pushes northward
overnight. Could result in another stratus layer, although meso
models favor keeping this south of the TAF sites. Will do the same.

WX/Vsby: sfc front slides west-east across the region today, and
will spark more showers/storms later in the afternoon/evening. The
front should be right around KLSE when convection starts to
peculate, but meso models suggest it will shift east before a sct-
bkn line can develop. Going to keep SHRA/TS out of the forecast for
the moment. May need a VCTS if confidence increases the threat will
be close - mostly in a 19-21z time frame.

With high pressure building in and winds becoming light, see some
threat for fog - more so where the rain has fallen this morning
and/or later today. Likely that would keep vsby reductions north of
the TAF sites. Will monitor and keep P6SM for now.

Winds: LLWS concerns will end quickly this morning at KLSE as the
gradient starts to sag and the low level jet streaks north. Winds
will shift to the northwest as a sfc front swings east, roughly 17z
for KRST and 20z for KLSE. Winds will lighten up tonight under the
influence of high pressure - light north and/or vrb03kt.

&&

.CLIMATE...Friday through Saturday
Issued at 357 AM CDT Wed Sep 20 2017

Several record high and warmest low temperatures may be tied or
broken from Friday into Saturday. This could potentially continue
into Saturday night and Sunday. However, the confidence was not
high enough to include them at this time.

The following are record high temperatures for Friday (September
22)...

Austin MN - 89F in 2005
Charles City IA - 94F in 1937
Decorah IA - 96F in 1937
La Crosse WI - 94F in 1895
Mauston WI - 90F in 1908
Medford WI - 88F in 1903
Neillsville WI - 90F in 1937
Prairie du Chien, WI - 90F in 1895
Rochester MN - 95F in 1908
Sparta WI - 91F in 1937
Winona MN - 90F in 2005

The following are record low temperatures for Saturday (September
23)...

Austin MN - 64F in 1940
Charles City IA - 67F in 1930
Decorah IA - 67F in 1937
La Crosse WI - 69F in 1937
Mauston WI - 62F in 1908
Medford WI - 64F in 1968
Neillsville WI - 65F in 1920
Prairie du Chien, WI - 67F in 1968
Rochester MN - 66F in 1920
Sparta WI - 65F in 1937
Winona MN - 64F in 2016

The following are record high temperatures for Saturday
(September 23)...

Austin MN - 87F in 1938
Charles City IA - 88F in 1937
Decorah IA - 90F in 1937
La Crosse WI - 91F in 1891
Mauston WI - 84F in 1908
Medford WI - 89F in 1937
Neillsville WI - 89F in 1933
Prairie du Chien, WI - 89F in 1933
Rochester MN - 92F in 1937
Sparta WI - 99F in 1937
Winona MN - 84F in 1939

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...Rieck
CLIMATE...Boyne



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