Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 182013

Area Forecast Discussion
National Weather Service La Crosse WI
313 PM CDT Fri May 18 2018

.SHORT TERM...(This evening through Saturday)
Issued at 313 PM CDT Fri May 18 2018

At 3 PM, east winds on the southern periphery of a Canadian high
pressure system continued to bring dry air into the Upper
Mississippi River Valley. While the radar and some of the meso
models (ARW, NMM, and HRRR) are trying to produce rain, the air
mass below 600 mb remains rather dry, so we have not been seeing
any of this rain reaching the ground. This trend should continue
for the remainder of the afternoon.

For tonight, we will remain in between low pressure systems. One
low pressure system, currently located over the Mid Mississippi
River Valley, will move northeast into the southern Great Lakes.
Meanwhile, a cold front will remain off to our northwest.

On Saturday, a cold front will move southeast through the area.
As low level moisture pools along and north of this front, there
may be enough instability for scattered showers and isolated
storms to develop across southeast Minnesota and in west-central
and north-central Wisconsin.

.LONG TERM...(Saturday night through Friday)
Issued at 313 PM CDT Fri May 18 2018

From Saturday night through Sunday, the models are in general
agreement that the precipitation will be found along and south of
Interstate 94. With limited instability, only expecting periodic
showers with this wave.

From Sunday night into Monday night, the models continue to differ
on the northern extent of showers. Both the GFS and GEM are
further northwest with the upper level short wave, so showers end
up occurring across much of the area. Meanwhile, the NAM and
ECMWF are further southeast with their upper level short wave and
also have the Canadian high a bit further south, so as a result
they have their rain remaining mainly south of Interstate 90.

From Wednesday through Friday, the models are in general agreement
that a short wave trough will slowly move from the Northern Plains
into the Great Lakes. This system will provide a chance of showers
and storms. With weak 0-3 and 0-6 km shear, not anticipating any
severe weather from these storms.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1222 PM CDT Fri May 18 2018

The upper level low over Illinois will become an open wave and
move toward lower Michigan through tonight. The ongoing showers
and storms with this system are expected to lift north/northeast
and will stay off to the east of both airports. However, the
increase in moisture as this system moves north might push some
lower clouds over the area along with allowing some fog to form.
With the light winds and mostly clear skies confidence is higher
that fog will form than the lower clouds, so have included a MVFR
visibility reduction for both airports while putting some MVFR
ceilings into a tempo group for late tonight and early Saturday
morning. These should both burn off by the middle of the morning
for VFR conditions into the afternoon. A weak cold front will
start to move across Saturday morning turning the winds to the
northwest and possibly allowing a few showers and storms to
develop during the afternoon.




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