Area Forecast Discussion
Issued by NWS La Crosse, WI

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432
FXUS63 KARX 211742
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1242 PM CDT Thu Sep 21 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM CDT Thu Sep 21 2017

At 3 AM, dense fog was being reported in central Wisconsin.
However, phone calls indicated that this fog was not widespread.
An hour ago, it looked like on our web camera that a stratus deck
was building over the valley. However, with drier air moving into
the region, this has dissipated. Due to this, not planning on
issuing a dense fog advisory at this time.

For this afternoon and evening, the 0-1 km mean layer CAPES will
climb into the 1 to 2K J/kg along and south of the warm front.
There will be some weak moisture transport along this front as it
moves north. While this occurring, the 700 mb temperatures will
also be warming into the 9 to 12C range. So there are questions
whether a few showers and storms may develop along and north of
this warm front during this time frame. With many of the meso
models suggesting that this is a possibility, added a small chance
of showers and storms to the forecast.

For late tonight, the models show that the elevated CAPES above
700 mb will climb up to 500 J/kg. Weak to moderate moisture
transport will develop ahead of a mid level shortwave trough
moving northeast through Minnesota and northwest Wisconsin. This
may result in a line of elevated showers and storms moving across
central Minnesota and northern Wisconsin. Both the NMM and ARW are
in good agreement with this scenario.

.LONG TERM...(Friday through Wednesday)
Issued at 352 AM CDT Thu Sep 21 2017

On Friday morning, the nose of the 850 mb and 700 mb moisture
transport will move off to the northeast as a shortwave trough
moves away from the region. The showers and storms north of
Wisconsin 29 will be moving away from the area.

On Friday afternoon, the 850 mb temperatures will climb to around
23C. These are 2 to 2.5 standard deviations above normal. Mixing
down this air mass super adiabatically generates high
temperatures in the lower and mid 90s. These temperatures will be
warm enough for some record high temperatures to be potentially tied
or broken. These can be found in the climate section below. With
dew points in the mid and upper 60s, heat indices will be in the
mid and upper 90s. There maybe even a few 100 to 105 values in the
river valleys.

From Friday night into Sunday night, the area will remain dry and
unusually warm. 850 mb temperatures will range from 18C to 20C.
These anomalies are still 1 to 2 standard deviations above normal.
While the temperatures aloft will not be as warm, abundant
sunshine and dry soils will allow temperatures to warm to near 90
on Saturday and into the mid and upper 80s on Sunday. These
temperatures will be warm enough for a few record high
temperatures to be tied or broken. Low temperatures through this
time period will range from mid 60s to lower 70s. These also will
be warm enough for a few warmest minimum temperatures to be
reached.

From Monday afternoon through Tuesday, a cold front will move
through the region. With 0-1 km mean layer CAPES up to 1000 J/kg,
there will be enough instability for showers and storms. At this
time it looks like the deep shear will be mainly post frontal, so
not anticipating any severe weather at this time. While the severe
weather threat looks low, the precipitable water values will be
around 1.6 inches and warm cloud layer depths will range from 3.5
to 4 km. This could result in very efficient rain producers.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1242 PM CDT Thu Sep 21 2017

Winds will be the main concern this TAF period. The prevalent wind
direction will be southeast, turning more southerly tonight. Wind
speeds will hold around 5-10 kt at KLSE and 10-15 kt with an
occasional afternoon gust near 20 kt at KRST through tonight.
Strong low-level wind shear will develop late this evening, with
southwesterly 2000 ft winds reaching 35-45 kt. While the wind
shear should weaken Friday morning, southerly surface winds will
increase to 10-15 kt, gusting to 20-25 kt by Friday afternoon.

The only concerns with regards to ceilings and visibility this TAF
period are diurnal cumulus clouds this afternoon. Visible
satellite imagery shows cumulus development just south of KRST as
of 21.17Z. Expect the cumulus field to expand throughout the
afternoon. Cloud bases will be in the 1500 to 3500 ft range, but
not anticipating more than SCT coverage, keeping VFR conditions
in place through the period.

&&

.CLIMATE...Friday through Sunday
Issued at 352 AM CDT Thu Sep 21 2017

It continues to look like several record high and warmest low
temperatures may be tied or broken from Friday into Sunday. The
tables below contain the record high and warmest low temperatures
through this time period.

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 - 92F in 1937

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 - 92F in 1937

The following are record low temperatures for Sunday (September
24)...

Austin MN - 63F in 2016
Charles City IA - 68F in 2007
Decorah IA - 65F in 1958
La Crosse WI - 71F in 1891
Mauston WI - 63F in 1958
Medford WI - 64F in 1920
Neillsville WI - 69F in 1930
Prairie du Chien, WI - 72F in 1930
Rochester MN - 67F in 1886
Sparta WI - 64F in 1958
Winona MN - 64F in 2015

The following are record high temperatures for Sunday (September
24)...

Austin MN - 84F in 2007
Charles City IA - 86F in 1935
Decorah IA - 90F in 1937
La Crosse WI - 92F in 1891
Mauston WI - 85F in 1984
Medford WI - 89F in 1908
Neillsville WI - 86F in 1908
Prairie du Chien, WI - 92F in 1984
Rochester MN - 88F in 1937
Sparta WI - 84F in 2008
Winona MN - 89F in 1935+

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...Hollan
CLIMATE...Boyne



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