Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220753

Area Forecast Discussion
National Weather Service La Crosse WI
253 AM CDT Tue Aug 22 2017

.SHORT TERM...(Today and tonight)
Issued at 252 AM CDT Tue Aug 22 2017

At 2 AM, a cold front extended from Green Bay to Dubuque Iowa.
The only precipitation associated with this front was located
near Lake Michigan and over southeast Iowa. A secondary cold front
extended from just east of Marquette Michigan southeast to
Des Moines. The only precipitation along this front is located
over western Upper Michigan and north-central Wisconsin. The
22.00z models are in good agreement that this secondary cold front
will move through the Upper Mississippi River Valley dry this

With 850 mb temperatures about 6C colder than they were on Monday,
high temperatures will only top out in the lower and mid 70s this

The combination of diurnal mixing and steep 900 to 800 mb lapse
rates today, expect the winds to be gusty from late morning into
the afternoon. Wind gusts will be in the 15 to 25 knot range.

With light winds expected this evening, expect a nocturnal
inversion to develop across central and north-central Wisconsin.
This along with clear skies will allow temperatures to fall into
the mid and upper 40s. This is more in line with the NAM guidance
than the GFS MOS guidance.

Like this morning, the soundings continue to show the boundary
layer will remain well mixed in the river valleys. As a result,
did not include any valley fog in the forecast grids.

.LONG TERM...(Wednesday through Monday)
Issued at 252 AM CDT Tue Aug 22 2017

On Wednesday night and Thursday morning, a short wave trough and
Canadian cold front will move southeast through the region. Both
the GFS and ECMWF are fairly similar with this feature. Meanwhile
the NAM is about 12 hours later. With the GFS being the most
consistent with this feature, trended the timing toward it. With
strong 900 to 500 mb frontogenesis and strong 295K isentropic
lift, expect a narrow band of showers to through areas south of
Interstate 94. Rainfall amounts will be up to a quarter of an
inch. Due to some uncertainty in timing and the location, kept
the rain chances in the 20 to 30 percent range for now. Once these
become more consistent these rain chances will likely have to be

From Thursday night into Friday morning, both the GFS and NAM has
another short wave moving through the region. Meanwhile the ECMWF
has its wave further west and southwest. Due to this uncertainty,
only have a 15 to 24 percent chance across southeast Minnesota and
northeast Iowa for now.

Looking ahead to the weekend and early next week, the models are
in good agreement that a narrow, elongated short wave trough will
move slowly east through the region. While this has been
consistent feature, there is uncertainty on how fast into will
move into and remain over the area. This is due to potential
tropical systems developing over the western Gulf of Mexico and
along the East Coast. Enhanced ridging inland ahead of these
systems could potentially slow its eastward advance into the
region. If this does not happen, this system could potentially
move quickly through the region. Due to this, kept the rain
chances in the 20 to 30 percent region.

With both the GFS and ECMWF not showing much instability from
Wednesday through Monday, did not mention any thunder in the


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1140 PM CDT Mon Aug 21 2017

Showers and thunderstorms have moved well east of TAF airfields
with dry conditions expected through the period. The primary
aviation concern overnight will be the potential for some MVFR
ceilings as a cold front moves through the region. Think potential
is greater at KRST, so added a TEMPO group from 22.09-22.13Z. Will
keep KLSE VFR for now, but bears watching. Much drier air will
move across the region after frontal passage, resulting in mostly
sunny/clear skies and northwest wind. Could see some gusts into
the lower 20 kt range late Tuesday morning/afternoon, before
diminishing later in the evening.




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