Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200857

Area Forecast Discussion
National Weather Service La Crosse WI
357 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

.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 06Z TAFS through 06Z Wednesday night)
Issued at 1142 PM CDT Tue Sep 19 2017

Watching a large line of thunderstorms from near KFSD to KROX,
moving northeast around 40 kts. For the most part, these storms
are expected to weaken as they move eastward overnight. However,
latest high resolution guidance suggests there could be a brief
period of showers/storms at TAF airfields, so added VCTS/CBs at
KRST from 20.10Z to 20.13Z and at KLSE from 20.12Z to 20.15Z.
Ahead of these storms, expect strong 40 to 50 kt southerly winds
in the 1500 to 2000 ft agl layer. With sustained surface winds
from 10 to 20 kts, expect low-level wind shear through the night,
diminishing after sunrise Wednesday morning.

In the wake of any thunderstorms Wednesday morning, ceilings
expected to drop to MVFR at times. May not be continuous for
hours on end, but for now will keep lower cloud bases until
early-mid afternoon. VFR conditions will return to end the period.
Surface winds will gradually shift to the west-southwest by
afternoon as a cold front moves across the region.


.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

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

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




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