Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 301951

Area Forecast Discussion
National Weather Service La Crosse WI
251 PM CDT Fri Sep 30 2016

.SHORT TERM...(This evening through Saturday)
Issued at 251 PM CDT Fri Sep 30 2016

Latest water vapor imagery indicating upper level cut-off/closed
low over the Ohio River Valley and shortwave ridge over the
Northern and High Plains. Pieces of energy rotating around the
upper level cut-off low is producing isolated/scattered showers
over parts of eastern Wisconsin and Illinois per latest mosaic

The 30.12z GFS/NAM/ECMWF are in good agreement in lifting upper
level closed/cut-off low into the Great Lakes Region tonight into
Saturday. A series of impulses wrapping around the upper level
cut-off low will continue to advect moisture into the area. Weak
lift in association with the impulses and dry air over much of
the forecast area...will inhibit the potential for showers across
the forecast area. With the better chances mainly east of the
Mississippi River and occurring late tonight into Saturday

.LONG TERM...(Saturday night through Friday)
Issued at 251 PM CDT Fri Sep 30 2016

Upper level cut-off/closed low tracks into the eastern Great
Lakes Region Saturday night and allows any isolated/scattered
showers to be east of the forecast area. Then...upper level ridge
amplifies/builds over the central United States/Great Lakes region
and provides dry weather across the forecast area Sunday into
Monday. Temperatures should warm into the 60s to around 70 degrees Monday.
If skies clear over the forecast area Sunday night...there is the potential
for fog formation in river the 30.12z GFS/NAM bufkit
soundings show inversion developing and deep layer light winds. At
this time...have left mention of fog out of the forecast.

Main forecast concerns are precipitation chances Tuesday night into
Thursday. Considerable differences occur between the deterministic
30.12z GFS/ECMWF/GEM through the the models differ on
strength of the upper level ridge amplifying over the central
United States Monday night/Tuesday and placement/timing of the
upper level closed low/trough slowly moving into the Upper Midwest
Tuesday night into Thursday. This will have impacts on timing of
the shower/thunderstorm chances and how widespread the
showers/thunderstorms will be across the forecast area Tuesday
night into Thursday. The 30.12z GFS/ECMWF/GEM continue to show
strong warm air advection out ahead of the upper level closed
low/trough Tuesday and will provide above normal temperatures
across the forecast area Tuesday. Slightly below normal
temperatures are expected later in the cooler air
filters into the forecast area behind surface front/upper level


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1208 PM CDT Fri Sep 30 2016

The surface low that has been over the Ohio River Valley has made
very slow northward progress which has resulted in the cloud
shield also making very little movement. These clouds have yet to
move into KRST and KLSE has been right on the edge resulting in
ceilings bouncing from VFR to MVFR. Not expecting much change in
this trend until this evening when enough of a northward shift in
the surface low should push the clouds farther to the northwest
and bring the MVFR ceilings into both airports. A decent short
wave trough rotating around the system should give enough forcing
to bring some light showers close to the Mississippi River
overnight but not expecting these to get into either airport. It
will help to lower the ceilings though, with both airports
expected to go down to IFR overnight. For now, have not include
any fog as the 30.12Z NAM forecast soundings again show winds of
15 knots or stronger just above the surface which should help form
the lower stratus clouds and not fog. The ceiling height should
gradually improve Saturday morning as the surface low starts to
move east and with some diurnal heating.




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