Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 171656
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1156 AM CDT WED AUG 17 2016

.SHORT TERM...(Today and tonight)
Issued at 325 AM CDT Wed Aug 17 2016

Latest water vapor satellite imagery showing shortwave trough over
eastern Minnesota and western Wisconsin and producing a complex of
showers and thunderstorms over central/southwest Wisconsin into
eastern/central Iowa...per latest mosaic radar.

Shortwave trough and associated lift/moisture convergence moves east
of forecast area today. Weak surface ridge builds into eastern
Minnesota and western Wisconsin today into tonight. Subsidence
behind shortwave trough and underneath surface ridge will allow for
showers/thunderstorms to diminish over the forecast area this
morning. Have confined small precipitation chances across parts of
northeast Iowa and eastern parts of the forecast area...where
residual weak moisture convergence located and diurnal heating may
produce an isolated shower/storm this afternoon.

Main forecast concern tonight is fog potential across the forecast
area. The 17.00z GFS/NAM suggest inversion developing...clear
skies and light winds will allow for the fog to develop across the
forecast area.

.LONG TERM...(Thursday through Tuesday)
Issued at 325 AM CDT Wed Aug 17 2016

Surface ridge builds into Michigan and southerly flow aloft on the
backside of ridge advects warmer airmass into the forecast area
Thursday. The 17.00z GFS/NAM suggest plus 24 to plus 25 degrees
celsius at 925mb by 21z Thursday. High temperatures will climb
into the middle to upper 80s across much of the forecast area.

Thursday night into Friday...The 17.00z GFS/NAM/ECMWF all show
significant differences on strength/placement and timing of
shortwave troughs embedded in the developing southwest flow aloft.
This will have impacts on the precipitation chances across much of
the forecast area during this time frame. The 17.00z GFS/NAM/ECMWF
dig upper level trough over the Northern Plains states and amplify
shortwave ridge over the Upper Midwest/Great Lakes region and over
much of the forecast area Thursday night into Friday. This would
result in main forcing/vertical motion and moisture convergence
over the northern parts of the forecast area and possibly north
and northwest of the forecast area. Higher shower/storm chances
will be across the northern parts of the forecast area and lesser
chances to mainly dry weather can be expected over the southern
parts of the forecast area Thursday night into Friday. At this
time...a few of the storms could be strong.

Focus turns to Friday evening into Saturday with upper level trough
tracking into the Upper Great Lakes Region. The 17.00z GFS/ECMWF/NAM
continue to show differences on placement of shortwave
trough/surface features. However...the deterministic models indicate
decent QG forcing/vertical motion and moisture convergence in
association with the upper level trough/surface features. Showers
and thunderstorms are likely across much of the forecast area. Next
concern is severe potential...The 17.00z GFS/NAM show much of the 0-
3km and 0-6km shear behind surface low/cold front Friday
evening/night. With the models indicating 0-6km most unstable
CAPE of 1500 to 3000 j/kg. The possibility exist...a few of the
storms could be strong to severe with damaging winds and hail.

Main forecast concerns Sunday into Tuesday are temperatures Sunday
into Monday. The 17.00z GFS/ECMWF are in better agreement in
deepening upper level trough over the Great Lakes region. As surface
cold front/surface low passes...colder air filters into the forecast
area Saturday night into Sunday. The 17.00z GFS/ECMWF drop 925mb
temperatures to plus 10 to plus 15 degrees celsius by 18z Sunday.
With upper level trough over the area...clouds/precipitation and
cooler temperatures aloft...temperatures will be well below
normal across the forecast area Sunday...with highs in the middle
60s to lower 70s. Unseasonably cool temperatures will continue
into Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1156 AM CDT Wed Aug 17 2016

Trough of low pressure will swing across the area this afternoon,
producing scattered to broken cumulus. Could see a few showers as
well, but thinking these will likely stay south of the KLSE/KRST
sites where better instability exists. Look for the cumulus to
dissipate after sunset. Concern then turns to what looks to be
another ideal setup for river valley fog which will impact KLSE
late tonight/early Thursday morning. Right now, thinking
fog/stratus will produce LIFR conditions at KLSE in the 10-13Z
timeframe.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...DAS



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