Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 131122

Area Forecast Discussion
National Weather Service La Crosse WI
622 AM CDT Wed Sep 13 2017

.SHORT TERM...(Today and tonight)
Issued at 255 AM CDT Wed Sep 13 2017

Latest 07z surface analysis shows elongated surface ridge
extending from the eastern Great Lakes region into Eastern Kansas.
With clear skies per infrared satellite imagery and light
winds has allowed areas of dense fog to form in mainly river
valleys and the favored areas in central Wisconsin.

Surface ridge will be the dominant weather today into tonight.
Southerly winds aloft will advect slightly warmer temperatures
into the forecast area the 13.00z GFS/NAM/ECMWF
indicate plus 20 to plus 24 degrees celsius over the forecast area
by 00z Thursday. Temperatures will remain above normal with highs
mainly in the lower to middle 80s.

.LONG TERM...(Thursday through Tuesday)
Issued at 255 AM CDT Wed Sep 13 2017

Upper level ridge builds into the eastern Great Lakes region and
upper level trough digs over the Rocky Mountains Thursday into
Friday. First piece of energy ejects out of the upper level trough
into the Northern surface warm front lifts north into
central Minnesota and northern Wisconsin Thursday/Thursday night.
The 13.00z GFS/NAM suggest weak moisture convergence and forcing
in association with this piece of energy and produce the
possibility of showers/thunderstorms mainly the western and
northwestern sections of the forecast area Thursday night. Have
kept shower/thunderstorm chances over this part of the forecast

Main forecast concerns Friday night through Tuesday are periodic
shower/thunderstorm chances Friday night into Sunday. The 13.00z
GFS/ECMWF remain consistent in ejecting impulses/lifting upper
level trough into the Northern Plains/Upper Midwest Friday night
into Sunday. With increasing moisture/vertical motion in
association with each impulse...periodic shower/thunderstorm
chances will continue Friday night into Sunday...with higher
chances occurring Saturday night/Sunday morning across the
forecast area. Differences occur between the 13.00z GFS/ECMWF
Monday into the GFS more progressive in moving next
shortwave trough into the Upper Midwest than the ECMWF.
Confidence in shower/thunderstorm chances are low...however
continue with small chances of showers/thunderstorms Monday into


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 622 AM CDT Wed Sep 13 2017

Some radiational valley fog will produce IFR/LIFR conditions at KLSE
and nearby river valley sites thru 13-15z. After that, good VFR
conditions are expected at both taf sites thru today/tonight.

The sfc high centered over the area that allowed valley fog to
develop the last couple mornings will shift south a bit today/
tonight. South gradient winds of 4-8kts are expected tonight, which
should keep any late night/early morning valley fog around 12z Thu
to a minimum.




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