Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191146
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
646 AM CDT Thu Oct 19 2017

.SHORT TERM...(Today and tonight)
Issued at 302 AM CDT Thu Oct 19 2017

At 3 AM, the water vapor imagery shows moisture streaming into
the Pacific northwest. This moisture then becomes embedded into
the zonal flow across the northern Plains and Canadian prairie
Providence and then moves east into the Upper Mississippi River
Valley and Great Lakes. Due to this upper level moisture, we have
increased the cloud cover across the area early this morning.

For today and tonight, the 19.00z models are in good agreement
that an upper level ridge will build quickly across the region.
As this occurs, the upper level moisture feed will be pushed north
of the area. As a result, expect mostly clear to clear skies
through much of this time period.

Moderate 925 mb warm air advection will develop across the
region today. The 925 mb temperatures will warm quickly to
between 12C and 15C by mid afternoon. This is much faster than it
looked like during the past couple of days. Due to this, raised
the high temperatures anywhere from 3 to 5F. It looks like the
high temperatures will be near 70 north of Interstate 94 and in
the lower and mid 70s elsewhere.

Soundings show that as we mix up to 925 mb that very dry air will
mix to the surface. This will drop dew points into the mid and
upper 20s. The combination of these temperatures and dew points
will lower afternoon relative humidities 15 to 25 percent range.
Fortunately, the wind speeds are not that particularly strong.

.LONG TERM...(Friday through Wednesday)
Issued at 302 AM CDT Thu Oct 19 2017

On Friday, a strong southerly flow will push 925 mb temperatures
into the 17 to 19C range. Mixing these temperatures down to the
surface results in temperatures ranging from the mid 70s to lower
80s.

Late Friday night and Saturday morning, 850 mb moisture transport
will increase across the area. This is in response to the long
wave trough approaching the region from the Plains. As this
moisture increases across the region, scattered showers will
develop across the area.

On Saturday afternoon and night, a cold front will move through
the region. Like the past couple of days, the 0-3 km wind shear
climbs into the 25 to 35 knot range, but the most unstable CAPES
are only up to 500 J/kg. As a result, not anticipating any severe
storms to develop ahead of this front.

On Sunday night and Monday, a cold front front will move through
the region. The ECMWF has slowed down and it is now more similar
to the timing of the GFS; thus, increased the temperatures for
these time periods. Also, removed the rain chances for that time
period.

On Monday night and Tuesday, much colder air moves into the
region. While the models are in good agreement with this, there is
some disagreement on where the deformation area will be located.
The GFS and ECMWF has this east of our area. Meanwhile the
Canadian has it over our area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 646 AM CDT Thu Oct 19 2017

VFR conditions are expected through the TAF period. Low level wind
shear will be the main concern in the TAFs tonight as winds
increase into the 35 to 40 kt range around 2kft by 01Z. The low
level wind shear will continue through much of the overnight
hours. Plan on increasing south winds today, especially at KRST,
where winds may gust to 18 kts.

&&

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

$$

SHORT TERM...Boyne
LONG TERM...Boyne
AVIATION...Wetenkamp


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