Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 140739

Area Forecast Discussion
National Weather Service La Crosse WI
239 AM CDT Thu Sep 14 2017

.SHORT TERM...(Today and tonight)
Issued at 239 AM CDT Thu Sep 14 2017

Latest water vapor satellite imagery indicates upper level trough
over the Pacific Northwest/British Columbia/Alberta Canada and
upper level ridge over the central High Plains. Latest 07z surface
analysis shows ridge over the Ohio River valley and latest metars
indicated patchy dense fog over the favored areas of central
Wisconsin and the Wisconsin River valley.

Upper level ridge begins to amplify over the central United
States today and allows warmer air aloft to advect into the
forecast area. The 14.00z GFS/NAM suggest 925mb rising to plus 22
to plus 24 degrees celsius by 00z Friday. Unseasonably warm
temperatures are expected with highs in the 80s...with some
locations approaching 90 degrees.

Tonight...first weak impulse embedded in southwesterly flow aloft
moves into southern Minnesota/western Wisconsin by 06z Friday. The
better moisture convergence/lift remains west of the forecast
area...however the leading edge of moisture convergence/lift will
be over the western and northwestern periphery of the forecast
area. Will continue with small chances of shower/thunderstorms
across southeast Minnesota...northeast Iowa and parts of western

.LONG TERM...(Friday through Wednesday)
Issued at 239 AM CDT Thu Sep 14 2017

Upper level trough continues to dig over the Rocky Mountains and
upper level ridge builds into the Great Lakes region Friday into
Saturday. Main axis of moisture transport and lift in association
with pieces of energy embedded in the southwesterly flow aloft
will remain west of the forecast area and provide dry weather/
unseasonably warm temperatures across the forecast area Friday.
The 14.00z GFS/NAM/ECMWF 925mb temperatures are progged to be in
the plus 22 degrees celsius to around plus 25 degrees celsius
range across forecast area. High temperatures will remain
unseasonably warm into Friday with highs in the 80s to around 90
at a few locations.

Focus then turns to Friday night into Sunday...upper level trough
lifts northward into southern Canada. Impulses ahead of the upper
level trough...along with the surface front move across the
forecast area during this period. The 14.00z deterministic models
continue to show increasing moisture transport/convergence and
vertical motion over forecast area and produce periodic
shower/thunderstorm chances. However...indications are the
forecast area will have the higher chances of
showers/thunderstorms Saturday night into Sunday morning in
association with the surface front.

Main forecast concerns are shower/thunderstorm chances Monday into
Wednesday. The 14.00z GFS/ECMWF differ considerably on strength of
upper level ridge over the central United States...where the GFS is
quicker in breaking down ridge than the ECMWF. If this is the
case...then the Upper Midwest region will remain in active weather
pattern into middle of next week. At this time...confidence remains
low based on the overall weather pattern and will maintain chances
of shower/thunderstorms through the period.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1145 PM CDT Wed Sep 13 2017

VFR conditions will continue across the region through the next 24
hours, save for some localized fog development in the usual river
valley locations across mainly Wisconsin. Periods of cirrus will
also advance across the area, giving way to a period of broken mid
level ceilings for RST tonight as moisture starts to increase
across the area. There is a very low end risk for a shower to
impact RST after 00Z tonight, though confidence just isn`t there
yet to include (and things would remain VFR even if it does
occur). Lighter south to southeast winds through sunrise will
increase from the south at 10-18 knots into the afternoon and
evening hours.




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