Area Forecast Discussion
Issued by NWS La Crosse, WI

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193
FXUS63 KARX 242316
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
515 PM CST Sat Feb 24 2018

.SHORT TERM...(This evening through Sunday)
Issued at 325 PM CST Sat Feb 24 2018

At 3 PM, a surface low was located over southwest Missouri. An
inverted trough extended north into southern Minnesota. Water
vapor imagery showed a negatively tilted short wave over western
Iowa and the 24.12z models continue to show that this system will
move quickly northeast across the area this evening. A light
wintry mix of precipitation was already spreading northeast into
areas south of Interstate 90. The precipitation mainly rain in
southwest Wisconsin and in the eastern portions of northeast Iowa
and southeast Minnesota. This was due to warm air being advected
into the region ahead of this system. This warm nose will move
quickly east of these areas during the early to mid evening. As
this occurs, the rain will transition over to snow. Due to this,
increased the snow totals some just southeast of the Winter Winter
Weather Advisory area. The valley locations will likely see up to
an inch. Meanwhile, the ridges will see anywhere from 1 to 3
inches. Further to the north and northwest in the Winter Weather
Advisory area, snow totals look to be in the 3 to 6 inch range.
Maybe some locally higher totals in Dodge County in southeast
Minnesota and Taylor County in north-central Wisconsin.

The highest snow rates (possibly 1 to 2 inches an hour) will occur
between 6 PM and 10 PM ahead of the dry slot. This is due to some
elevated CAPES (up to 100 J/kg). Fortunately, this will be moving
through the region rather quickly.

As far as icing, it looks to be minimal due to the faster
transition from snow to rain. Due to this, the icing amounts were
lowered across northeast Iowa and central Wisconsin.

Strong subsidence in the wake of this short wave trough will
result in wind gusts of 25 to 35 mph in northeast Iowa, southeast
Minnesota, and north of Interstate 94 in Wisconsin. This will
result in some drifting snow.

.LONG TERM...(Sunday night through Saturday)
Issued at 325 PM CST Sat Feb 24 2018

On Tuesday afternoon and night, a cold front will move through
the region. Initially this system has little moisture with until
it gets south of Interstate 90. The boundary layer temperatures
will be warm enough initially warm for rain and then it will
gradually transition to snow. With the QPF very light, no impacts
are anticipated.

From Wednesday night into Thursday night, both the deterministic
GFS and ECMWF have a very strong short wave trough ejecting out of
the Central Plains. They both move the surface low through western
and northern Illinois. These models are much stronger than the
regional Canadian which has a similar track. There are some
tremendous snow totals showing up in both the GFS and ECMWF.
However, the GEFS plumes shows that the 24.12z deterministic GFS
run is a definite outlier compared to its family members when
looking at its snowfall and precipitation. In some locations, it
is 1 to 1.5 inches higher with its precipitation and over 10
inches higher with its snowfall than any other member. Looking at
the various individual members in the GFS and ECMWF, there is
huge uncertainty with this system with its strength and track. It
is not surprising that there is anywhere from 2 to 6 standard
deviation difference in the maximum and minimum temperatures. For
example, the high temperatures on Thursday range from lower 30s
to mid 40s. This would make even the precipitation type forecast
highly uncertain. Due to this, just stayed with a model blend for
now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 515 PM CST Sat Feb 24 2018

Cigs/WX/vsby: lifr/ifr cigs expected into the overnight hours as the
storm system sweeps across the region. Snow the predominant pcpn
type, although some rasn mix possible at KLSE at the outset. Sub 1sm
vsbys in the snow. Increasing winds overnight could lead to BLSN for
several hours at KRST, and some MVFR vsbys. The bulk of the pcpn
will exit northeast between 04-06z at the TAF sites, with clearing
of the low cigs after (or near) 12z Sun.

Winds: swing from east to west/southwest between 04-06z tonight as
the sfc low moves across the region. Winds will increase and become
gusty post the low, which could result in some blowing snow for
KRST. Winds should stay relative strong and gusty into Sun
afternoon, decreasing Sun evening as the pressure gradient relaxes.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 AM CST Sunday for WIZ032>034.

     Winter Weather Advisory from 6 PM this evening to 6 AM CST
     Sunday for WIZ017-029.

MN...Winter Weather Advisory until 6 AM CST Sunday for MNZ079-
086>088-     094-095.

IA...Winter Weather Advisory until 6 AM CST Sunday for IAZ008-009-
018-     019.

&&

$$

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



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