Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 121136
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
636 AM CDT Sat Aug 12 2017

.SHORT TERM...(Today through Tuesday)
Issued at 210 AM CDT Sat Aug 12 2017

Weekend shaping up to be quite a nice one as high pressure remains
the main weather influence for the region. Ample sunshine today, but
some high/mid level clouds expected to encroach from the west later
tonight, and could temper/filter some of that sunshine for Sunday.
If it stays mostly clear tonight, setup favors widespread valley
fog.

The GFS and NAM have been in good agreement with taking a shortwave
trough currently churning over MT east/southeast today, gradually
sliding it across the local area Sun afternoon/night. Not much
instability or wind shear to play with. A little low level moisture
transport to help fuel rain/storm chances. The deeper saturation
holds off until late Sunday/Monday - and the bulk of the
shower/storm chances could hold off until then.

.LONG TERM...(Wednesday through Friday)
Issued at 210 AM CDT Fri Aug 11 2017

Models remain in good agreement with a mid week system, taking an
upper level shortwave trough from the pac nw eastward, sliding it
across portions of the Upper Mississippi River Valley late Wed
through Thu (potentially into Friday). Previous runs of the GFS and
EC both suggested the shortwave would track across the U.S/Canadian
border, with the bulk of the upper level energy holding there. It`s
associated sfc front, coupled with low level moisture return and
some instability would have the most influence on rain chances
locally. Latest GFS run is farther south with the main piece of
upper level energy, resulting in greater qpf and higher threat for
showers/storms in the south. Both gradually shift the system into
the eastern great lakes. The previous EC run was slower, lingering
pcpn into Fri, but more on pace with the GFS now. However, the GFS
would bring another shortwave down across the region Friday. The EC
shows something similar, but weaker and faster. The GFS paints a
good shot for another round of showers/storms...the EC favors dry.
Feel good about the rain threat for late Wed into Thu, shakier with
the details for Friday. Don`t see much of a severe potential at this
time - some instability but weak wind shear.

Both the GFS and EC do hold the promise of high pressure for next
weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 636 AM CDT Sat Aug 12 2017

while not out of the question that a brief period of valley
stratus could impact KLSE early this morning, confidence is not
high enough to mention. Otherwise, high pressure will impact the
region through the TAF period with mainly VFR conditions
persisting. Winds will remain light through tonight with a few
diurnal cumulus possible this afternoon ahead of increasing high
clouds later tonight. Near the end of this TAF period there will
be potential for early morning valley fog/stratus at KLSE with
more favorable light winds extending up to 4-5 kft under the
surface high. One potential limiting factor would be the expected
increasing cloud cover early Sunday morning, depending on timing
and thickness. As a result, will not yet introduce any
visibility/ceiling restrictions, but will add BCGFG near the end
of the TAF valid period.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...JM



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